JP4192804B2 - Engine performance prediction analysis method, prediction analysis system and control program thereof - Google Patents

Description

  The present invention relates to a predictive analysis method, a predictive analysis system, and a control program for predicting engine performance by analyzing the motion of a working fluid using CFD (Computational Fluid Dynamics).

  Conventionally, in order to evaluate the performance of an engine, a transmission, etc., various measurement / test methods as disclosed in Patent Document 1, for example, have been proposed. Patent Document 2 discloses a simulation system that can evaluate powertrain performance without waiting for completion of engine development.

  As such a simulation technique, it is generally performed to analyze engine intake / exhaust flow and combustion gas motion by applying CFD and to predict engine performance based on the analysis result. That is, for example, a virtual experiment (simulation) for simulating a complicated flow of intake air sucked from the intake port into the combustion chamber by numerical calculation using a computer is performed, and for example, the shape of the intake port is determined based on the result of the simulation. As a result, it is possible to reduce the development man-hours spent on repeating trial productions and experiments, and to perform efficient design and development.

  Especially in recent years, the remarkable progress in computer computing power has made it possible to simulate the complex shape of intake ports and the flow of intake air in three dimensions without actually prototyping the engine. It is possible to predict changes in intake flow resistance and cylinder volumetric efficiency when the intake port shape is changed.

  Nonetheless, there is no simulation system that can simulate the flow of intake air and exhaust gas associated with engine operation in three dimensions. Even though the computer's computing power has improved, the shape of the intake / exhaust passage that differs for each cylinder of a multi-cylinder engine, the situation of gas exchange in the combustion chamber, and the burned gas that blows out from the combustion chamber to the exhaust system. This is because it is unrealistic to describe all gas flows and the like as three-dimensional flows.

  Therefore, in order to predict the overall performance of an engine (output, drivability, emissions, etc.), for example, first, experimental data obtained by investigating various performance characteristics of the engine are accumulated, and the performance Build a database that statistically correlates characteristics. At the same time, simulation is performed using a simple physical model (analysis model, numerical calculation model) that simulates the flow of intake and exhaust as a one-dimensional flow. The engine performance is predicted by combining knowledge obtained from the performance characteristic database and one-dimensional simulation results.

  In addition to the one-dimensional simulation using the simple model as described above, for example, a simulation that simulates only the intake air flow in the intake port in three dimensions is also performed, and analysis is performed by considering both results in combination. Improvement of the accuracy is also carried out. However, such a three-dimensional CFD analysis program is generally difficult to handle and has a lot of know-how required for setting to improve accuracy, and the load is concentrated on a dedicated analysis engineer. There was a tendency to delay development due to lack.

  In this regard, the inventors of the present application are based on a simple physical model that simulates the intake / exhaust flow of the engine as a one-dimensional flow as described above, and a part of this model is automatically three-dimensionally as necessary. We have developed a system that can be operated by replacing the model. In this system, the overall intake / exhaust flow of the engine is calculated using a simple one-dimensional model, and a three-dimensional model is used for parts that require particularly high analysis accuracy. A boundary condition is given from the obtained flow field data, and a three-dimensional CFD calculation is automatically performed.

In addition, this system employs a user-friendly interface and also automates troublesome settings specific to the three-dimensional CFD analysis program so that even a dedicated analysis engineer can easily handle it. .
Japanese translation of PCT publication No. 2002-526762 JP 2002-148147 A

  By the way, when the boundary condition of the three-dimensional CFD calculation is given from the flow field data obtained by the one-dimensional CFD calculation as in the above-described system, the three-dimensional CFD model is obtained by the one-dimensional CFD calculation. Only the average values of the flow variables at the inlet side and outlet side boundary surfaces of the first and second flows are considered to be substantially uniform and unbiased at the respective boundary surfaces, and the average flow variable values are directly used as the boundary values. It is possible to develop the entire surface.

  However, in general, the flow of intake / exhaust air in the passage is not uniform in the cross-section, and shows a flow velocity distribution that becomes relatively slow due to viscosity, for example, near the passage wall surface, and becomes faster as the distance from the passage wall surface increases. Further, when the passage is curved, the flow of the outer portion tends to be faster than the curved inner portion.

  Further, the flow of intake and exhaust of the engine is partially unsteady flow with very large fluctuations. For example, in the independent exhaust passage of the exhaust manifold, the exhaust flow of the cylinder is changed from a relatively low speed state where the exhaust flow can be regarded as laminar flow. The flow state changes greatly to the turbulent flow state where the burned gas is blown out at a high speed with the valve opened, and the flow velocity distribution in the cross section of the passage greatly changes accordingly.

  For example, when the exhaust flow in the exhaust manifold is simulated in a three-dimensional manner, the boundary surface of the three-dimensional model is provided at a portion where the flow velocity distribution of the exhaust gas in the passage cross section changes greatly during engine operation as described above. In such a case, if the exhaust flow velocity is considered to be substantially constant over the entire boundary surface, the speed difference between adjacent calculation grids (mesh) near the boundary surface of the model is excessively large. As a result, the calculation is diverged and the system may be down.

  In order to suppress the divergence of such calculation, for example, the mesh may be divided very finely in the vicinity of the boundary surface, and if a low-order one is adopted as the discretization method (scheme) of the basic equations, so-called numerical values are used. It is also known that stability is increased by the action of viscosity, but using such a fine mesh has the difficulty of directly increasing the calculation time, and a low-order scheme should be adopted. If this is the case, a decrease in analysis accuracy is inevitable.

  The present invention has been made in view of such a point, and an object of the present invention is to analyze the flow of intake and exhaust of the engine by at least one-dimensional and three-dimensional CFD calculations, thereby predicting the performance of the engine. Divergence of calculation while improving the accuracy of analysis and shortening the calculation time by devising the method of expanding the flow variable value obtained by one-dimensional CFD to the three-dimensional boundary surface. Is to prevent the system from going down.

  In order to achieve the above-described object, in the present invention, the flow uneven distribution of the boundary surface, which differs depending on the size / shape of the intake / exhaust passage, the flow state, etc., is previously examined and set, and the one-dimensional and three-dimensional CFD When performing calculations in parallel, an appropriate bias distribution is selected based on the result of the one-dimensional CFD calculation, thereby obtaining a boundary condition in which flow variable values are appropriately distributed on a three-dimensional boundary surface. did.

  More specifically, the invention of claim 1 is a one-dimensional CFD that simulates an intake / exhaust flow from at least a part of an intake system to a part of an exhaust system of an engine using a one-dimensional CFD analysis model. A program, a three-dimensional CFD program for simulating an intake / exhaust flow in a predetermined part of the intake system or exhaust system using a three-dimensional CFD analysis model, and a flow calculated by at least the one-dimensional CFD program A data exchange program for providing boundary conditions for computation by the three-dimensional CFD program based on the field data, and the computer program is executed in parallel to analyze the flow of intake and exhaust, The target is a predictive analysis method that predicts engine performance.

  In such an analysis method, the uneven distribution of the intake and exhaust flows at the inlet side and outlet side boundary surfaces of the three-dimensional CFD analysis model is respectively examined, and this bias distribution is associated with at least the shape of each boundary surface in advance. Set as. Then, based on the flow field data obtained by the one-dimensional CFD calculation, the value of the flow variable of each boundary surface is obtained according to the flow distribution of each boundary surface set in the database, and this is obtained as a three-dimensional CFD. Boundary condition for operation.

  According to the above method, first, in the simulation for simulating the operating state of the engine, by analyzing the flow of intake and exhaust using at least one-dimensional and three-dimensional CFD analysis models, for example, volume efficiency, loss factor, etc. The engine's physical characteristics can be obtained and performance characteristics such as engine output and fuel consumption can be predicted. At that time, the entire flow of intake and exhaust is simulated as a one-dimensional flow, and only a predetermined part where the flow of intake and exhaust is particularly important in performance prediction is simulated as a three-dimensional flow, while ensuring sufficient prediction accuracy. The calculation time can be shortened.

  When CFD calculation is performed by combining analysis models with different dimensions, the one-dimensional calculation results are matched so that the flow states coincide with the one-dimensional calculation results at the inlet side and outlet side boundary surfaces of the three-dimensional analysis model. The calculation result data is passed as a boundary condition. Since the one-dimensional calculation requires the average value of the flow variables at each boundary surface of the three-dimensional model, the entire boundary surface is based on this. It is necessary to determine the value of the flow variable distributed in

  In view of this, at least a basic deviation distribution of a flow that differs depending on the shape of each boundary surface is previously examined and set, and when the one-dimensional and three-dimensional CFD operations are performed in parallel as described above, the one-dimensional Based on the average value of the flow variables (for example, the pressure, density, flow velocity, temperature, etc. of intake / exhaust) on each boundary surface obtained by CFD calculation, the entire boundary surface is determined according to the flow bias distribution set in the database. Determine the value of the flow variable.

  In this way, a boundary condition reflecting a greatly different flow deviation depending on the shape of the intake / exhaust passage and the flow state can be given to the three-dimensional CFD calculation. Large deviations in the flow variables between meshes can be suppressed, and calculation can be done without dividing the mesh particularly finely, using a low-order scheme, or changing the value of the relaxation coefficient. Can be prevented from diverging.

  Next, the invention of claim 2 of the present application includes a one-dimensional and three-dimensional CFD program for simulating the intake and exhaust flow of the engine using a one-dimensional and three-dimensional CFD analysis model, respectively. The object of the present invention is a predictive analysis system in which a program is executed in parallel to analyze an intake / exhaust flow from at least a part of an intake system to a part of an exhaust system, thereby predicting engine performance.

  Then, using the one-dimensional CFD analysis model, a first CFD calculation means for calculating a flow field of intake / exhaust from at least a part of the intake system to a part of the exhaust system, and the first CFD calculation means Based on the flow field data, boundary condition providing means for giving a boundary condition for CFD calculation by the three-dimensional CFD program, and based on the boundary condition given by the boundary condition giving means, the three-dimensional CFD program is Second CFD calculation means to be executed, and bias distribution setting means for setting the bias distribution of the intake and exhaust flows at the inlet and outlet side boundary surfaces of the three-dimensional CFD analysis model based on at least the shape of the boundary surfaces. In addition, based on the flow field data calculated by the first CFD calculating means, the boundary condition applying means is configured to apply the bias distribution. Seeking the value of the respective boundary surfaces overall flow variable according biased distribution of the flow of the boundary surface set by the constant section, and shall be the boundary conditions of the three-dimensional CFD operation this.

  According to the predictive analysis system described above, in the simulation for simulating the operating state of the engine, a one-dimensional CFD program is basically executed by the first CFD calculating means, and the calculated flow field of the entire intake and exhaust is calculated. Based on the data, a boundary condition for the CFD calculation by the three-dimensional CFD program is given by the boundary condition providing means, and the three-dimensional CFD program is executed by the second CFD calculation means using this boundary condition.

  At that time, the bias distribution of the intake and exhaust flows at the inlet side and outlet side boundary surfaces of the three-dimensional CFD analysis model is set by the bias distribution setting means based on at least the shape of the boundary surfaces, and the flow of the flow thus set is set. According to the bias distribution, based on the flow field data calculated by the first CFD calculating means, the boundary condition providing means obtains a flow variable value of the entire boundary surface, and this is used as the boundary condition of the three-dimensional CFD calculation. 2 CFD calculation means. That is, it is possible to automatically execute the predictive analysis method according to the first aspect of the present invention and easily obtain the effects thereof.

  Here, since the flow bias distribution is basically set based on the flow of a compressible viscous fluid in the pipe, the flow is relatively fast near the center of gravity at each boundary surface of the three-dimensional analysis model. On the other hand, it is preferable to distribute the flow rate of the intake and exhaust air in a layered manner so as to be relatively slow near the passage wall (invention of claim 3). Further, when the intake / exhaust passage simulated by the analysis model is curved in the vicinity of the inlet-side boundary surface, it is preferable to shift the fastest flow portion of the inlet-side boundary surface to the outside of the curved passage. In addition, when the intake / exhaust passage simulated by the analysis model is curved, it is preferable to reflect the flow deviation generated at the outlet side boundary surface in the flow deviation distribution of the outlet side boundary surface. (Invention of Claim 5).

  Further, the flow velocity distribution as described above is based on the flow field data calculated by the first CFD calculation means, taking into consideration that the flow varies greatly depending on whether the flow is laminar or turbulent. More preferably, it is determined whether the flow at each boundary surface is in a laminar flow state or a turbulent flow state, and the flow bias distribution is changed and set according to the determination result (invention of claim 6). In this way, even when the flow transitions between the laminar flow state and the turbulent flow state in the middle of the analysis, the boundary condition can be appropriately given regardless of this.

  More specifically, in the predictive analysis system, the distribution distribution of the intake and exhaust flows at each boundary surface is associated with at least the shape of each boundary surface, and the flow is laminar and turbulent. It is preferable to provide a separately set database. In this way, the bias distribution is set by obtaining the flow state at each boundary surface based on the flow field data calculated by the first CFD calculating means and reading out the corresponding flow bias distribution from the database. (Invention of claim 7).

  Alternatively, the predictive analysis system includes a database in which the bias distribution of the intake and exhaust flows at each boundary surface is set in association with at least the shape of each boundary surface and the simulated operation condition of the engine, and the bias distribution setting means includes the database It is also possible to read and set the flow bias distribution corresponding to the simulated operation condition from the above (invention of claim 8).

  Next, the invention of claim 9 of the present application includes a one-dimensional and three-dimensional CFD program for simulating the intake and exhaust flow of the engine using a one-dimensional and three-dimensional CFD analysis model, respectively. Targeting the control program of the predictive analysis system that executes the program in parallel and analyzes the flow of intake and exhaust from at least part of the intake system to part of the exhaust system, thereby predicting the engine performance And

  Then, using the one-dimensional CFD analysis model, the first CFD calculation step for calculating the flow field of the intake / exhaust gas from at least a part of the intake system to the part of the exhaust system and the first CFD calculation step are used. Based on the flow field data, a boundary condition providing step for giving a boundary condition for CFD calculation by the three-dimensional CFD program, and the three-dimensional CFD program based on the boundary condition given in the boundary condition giving step A second CFD calculation step to be executed, and a bias distribution setting step for setting the bias distribution of the intake and exhaust flows at the inlet side and outlet side boundary surfaces of the three-dimensional CFD analysis model based on at least the shape of the boundary surfaces. In addition, in the boundary condition applying step, the flow field data calculated in the first CFD calculating step Based, the seeking the value of the respective boundary surfaces overall flow variable according biased distribution of the flow of the boundary surface set in uneven distribution setting step, it is assumed that the boundary conditions of the three-dimensional CFD operation this.

  By controlling the computer system by the control program, the computer system becomes an engine performance prediction analysis system according to the invention of claim 2, and the same operation effect as that of the invention of claim 2 is thereby obtained.

  As in the inventions of the third to fifth aspects, in the bias distribution setting step, the flow is relatively fast near the center of gravity of each boundary surface, and is relatively slow near the passage wall. Preferably, the flow velocity of intake and exhaust is distributed in layers (invention of claim 10). When the intake and exhaust passage simulated by the analysis model is curved in the vicinity of the inlet side boundary surface, the flow is caused at the inlet side boundary surface. It is preferable to shift the fastest part to the outside of the curve of the passage (invention of claim 11), and when the intake / exhaust passage simulated by the analysis model is curved, this causes a flow deviation generated at the outlet side boundary surface Is preferably reflected in the uneven distribution of the flow at the outlet side interface (the invention of claim 12).

  Further, in the bias distribution setting step, it is determined whether the flow at each boundary surface is a laminar flow state or a turbulent flow state based on the flow field data calculated in the first CFD calculation step, and according to the determination result It is more preferable to change and set the flow distribution. Thus, the same effect as that attained by the 6th aspect can be attained.

  Further, the predictive analysis system associates the distribution of bias of the intake and exhaust flow at each boundary surface of the three-dimensional CFD analysis model with at least the shape of each boundary surface, and when the flow is in a laminar flow state and a turbulent flow state. And the bias distribution setting step includes the flow distribution distribution corresponding to the flow state at each boundary surface based on the flow field data calculated in the first CFD calculation step. It is preferable to read out and set from the database (invention of claim 14). Thus, the same effect as that attained by the 7th aspect can be attained.

  Alternatively, it comprises a database in which the bias distribution of the intake and exhaust flows at each boundary surface is set in association with at least the shape of each boundary surface and the simulated operation condition of the engine, and in the bias distribution setting step, the simulated operation condition is calculated from the database. It is also possible to read out and set the flow bias distribution corresponding to the above (invention of claim 15).

As described above, according to the engine performance prediction analysis method, the prediction analysis system, and the control program thereof according to the present invention, the one-dimensional and three-dimensional CFD operations are performed in parallel, thereby the flow of intake and exhaust of the engine. When the engine performance is predicted by analyzing the above, the flow distribution of the boundary surface, which varies greatly depending on the shape of the intake / exhaust passage, the flow state, etc., is set in advance, and the appropriate distribution based on the result of the one-dimensional CFD calculation is set. Since the bias distribution is determined and the value of the flow variable on the three-dimensional boundary surface, that is, the boundary condition is determined in accordance with this, the three-dimensional CFD calculation performed under this appropriate boundary condition is generally performed. The system is highly accurate using a high-order scheme, and while reducing the time by calculating with a relatively coarse mesh, system downtime due to divergence of calculation is prevented. It can be.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

(Overall system configuration)
FIG. 1 is a conceptual diagram showing an overall configuration of an engine performance prediction analysis system A according to an embodiment of the present invention. This system simulates the flow of intake and exhaust, which are working fluids of the engine, by one-dimensional and three-dimensional CFD computations, and simulates combustion in a cylinder by a chemical reaction equation, and combines them, Driving simulation is performed. This system is characterized by automating data exchange between one-dimensional and three-dimensional CFD computations and data exchange between CFD computations and chemical reaction simulation (chemical reaction SIM), for example, a throttle valve The flow of intake and exhaust from the cylinder to the catalytic converter can be dynamically simulated, so that extremely high-precision analysis can be easily performed.

  Reference numerals 1, 1,... Shown are computer apparatuses that mainly execute CFD operations. In this embodiment, in particular, a plurality of high-speed server computers are arranged in parallel in order to cope with an enormous amount of operations of three-dimensional CFD. Connected and used (hereinafter referred to as “calculation server”). Each of these arithmetic servers 1 incorporates a storage device such as a hard disk drive and is connected to an image display device 10 such as a display. Further, although not shown, an output device such as a printer and a keyboard for accepting an input operation by an operator. An input device such as a mouse is also connected. The storage device includes at least one-dimensional and three-dimensional CFD programs for simulating the flow of intake and exhaust, a dedicated preprocessor for constructing a physical model (analysis model, numerical calculation model) therefor, and a combustion state Are stored, and a chemical reaction simulation program for simulating the image and an image processing program for displaying an image of a simulation result by each of the programs.

  The arithmetic servers 1, 1,... Can access the model database DB11 by a general method as needed during the operation. The model DB 11 stores a physical model of an engine used for one-dimensional and three-dimensional CFD calculations, and stores the model in a state classified for each part of the engine. A model newly constructed by the preprocessor is also stored. The model of the physical model is a basic part of a portion where intake or exhaust flows, such as an intake system surge tank, independent intake passage, intake port, exhaust system exhaust port, exhaust manifold, EGR passage, etc. A part model that simulates a shape and whose physical property values such as dimensions, shape and material, surface state, and thermal conductivity can be changed, and is hereinafter referred to as a template part in this embodiment.

  By providing the model DB 11 in which the data of the template part that can change the dimension, shape, and physical property value is stored, the dimension, shape, and the like of the template part read from the model DB 11 are corrected and combined. If a calculation grid (mesh) is generated inside, a physical model of the engine for CFD calculation can be constructed. In addition, since the model once constructed in this way is also stored in the model DB 11, the model can be corrected as necessary, and the engine design can be easily coped with.

  Further, the operation servers 1, 1,... Can access the CFD operation database DB12 by a general method as needed during the operation. The CFD operation DB 12 stores various data used for the CFD operation, in addition to calculation conditions such as the time interval of the calculation in the CFD operation, the discretization scheme, the relaxation coefficient, and the like. For example, in the CFD calculation DB 12, as will be described in detail later, an intake / exhaust flow bias distribution at each boundary surface on the inlet side and the outlet side is set in association with a three-dimensional physical model stored in the model DB 11. Bias distribution data is stored.

  Further, the arithmetic servers 1, 1,... Can access the chemical reaction database DB13 by a general method as needed during the operation. This chemical reaction DB 13 is filled with a cylinder combustion chamber of an engine and contributes to combustion with representative ones of various gas components (chemical species) in intake air having various physical quantities representing the state in the cylinder. They are stored in a state of being grouped in advance in association with the set. Therefore, as will be described in detail later, according to the state in the cylinder obtained as a result of the CFD calculation, a corresponding group of gas components is read from the chemical reaction DB 13, and the chemical reactions of these gas components are respectively simulated. By this, the combustion state can be simulated.

  Reference numeral 2 shown in the figure is a computer device that is connected to an experimental data database DB 14 (experiment DB) that mainly stores engine specification values, physical characteristics, and performance characteristics in association with each other and manages the data ( Hereinafter, this is referred to as an experimental DB server). In other words, the data accumulated in the past experiments and developments related to engines and transmissions are organized by well-known statistical analysis methods, and the engine specifications and their physical characteristics (for example, volumetric efficiency, combustion characteristics, loss factor, etc.) Etc.) and their performance characteristics (for example, output, fuel consumption, emission, etc.) are stored in the experiment DB 14 as empirical formulas associated with each other. Based on this empirical formula, for example, performance characteristics can be predicted from engine specification values and physical characteristics.

  Reference numeral 3 shown in the figure is a computer device of a three-dimensional CAD system for supporting engine design (hereinafter referred to as a design CAD server). The design CAD server 3 executes a general-purpose CAD program for machine design and structural analysis, and accesses the design database DB15 (design DB) by a general method as necessary during the operation. It is possible to call engine design CAD data, or change them and store them in the design DB 15 anew. That is, three-dimensional design CAD data of various engines is stored in the design DB 15 in a state where it can be individually extracted and used for each part of the engine.

  Reference numerals 5, 5,... Are terminals (PC terminals) each formed of a personal computer, which are arranged in plural in the powertrain design department, development department, experimental department, etc. Are connected to the calculation servers 1, 1,..., The experiment DB server 2 and the design CAD server 3 so as to be capable of bidirectional communication. When the system control program is executed in accordance with the operation of the operator in each PC terminal 5, each PC terminal 5 is connected to the calculation servers 1, 1,... Via the network 6 (login). A so-called server / client environment is configured, and commands and files are exchanged mainly with the computing servers 1, 1,..., Thereby executing an engine operation simulation.

  The experiment DB server 2, the design CAD server 3, and the PC terminal 5 each have a built-in storage device such as a hard disk drive, as in the calculation server 1, and are connected to a display 10, an output device, an input device, and the like. Yes.

(CFD calculation)
Next, the operation simulation of a 4-cycle 4-cylinder gasoline engine will be described as a specific example of the one-dimensional and three-dimensional CFD.

  In this example, in order to shorten the time required for the CFD calculation as much as possible, a part of the engine is replaced with a three-dimensional CFD as necessary while basically using a one-dimensional CFD. That is, for example, as shown in FIG. 2A, a one-dimensional CFD physical model M1 from the throttle valve thv upstream of the intake passage of the engine to the catalytic converter cat through the combustion chambers of the first to fourth cylinders c1 to c4 is obtained. Basically, for example, when the main purpose of the analysis is to examine the deviation of the exhaust flow flowing into the catalytic converter cat, the exhaust manifold exm is replaced with a three-dimensional model M3 as shown in FIG. is there.

  More specifically, in the illustrated one-dimensional model M1, an independent intake passage from the surge tank st to each of the cylinders c1 to c4 and a common intake passage from the throttle valve thv to the surge tank st are basically provided. Are respectively represented as a collection of pipes, and similarly, an independent exhaust passage from each cylinder c1 to c4 to a collection portion of the exhaust manifold exm, and a common exhaust passage from the exhaust collection portion to the inlet of the catalytic converter cat, respectively. Expressed as a collection of tubes. The surge tank st and the first to fourth cylinders c1 to c4 are represented as containers. Although not shown in the figure, the EGR passage for returning a part of the exhaust from the collection portion of the exhaust manifold exm to the upstream of the surge tank st may be represented as a collection of pipes.

  In such a one-dimensional model M1, the flow of intake and exhaust flowing in the pipe is regarded as a one-dimensional flow of a compressible viscous fluid, and each of pressure p, density ρ, velocity u, and temperature T representing the state of the flow. The well-known equations for mass conservation, momentum conservation and energy conservation are solved by numerical calculation under given operating conditions (simulated operating conditions). That is, the value of the flow variable is calculated using a characteristic equation obtained by, for example, the characteristic curve method based on each of the conservation equations, and the intake / exhaust flow from the throttle downstream to the catalyst upstream is calculated in predetermined time increments (for example, crank Describe each angle. At this time, it is assumed that the internal state of the container is uniform and the fluid flowing in from the pipe is instantaneously and uniformly distributed. Further, an appropriate boundary condition is given at the joint portion between the tubes or between the tube and the container. Further, it is preferable to consider the influence of the bending condition of the pipe, friction on the wall surface, heat loss, and the like.

  On the other hand, the three-dimensional model M3 of the exhaust manifold exm simulates the shapes of the independent exhaust passages s1 to s4 and the downstream common exhaust passages s5 for each cylinder, for example, on the inner wall surface of these passages. A layer mesh of a predetermined size is pasted, and the mesh is cut into a space in the passage and divided into calculation grids. In the three-dimensional CFD, the exhaust flow in the passage is regarded as a three-dimensional flow of a compressible viscous fluid, and the respective conservation equations are solved as in the case of the one-dimensional case. That is, the flow field in the passage is calculated under the boundary condition given by the one-dimensional CFD calculation or the chemical reaction SIM described later, using, for example, a difference equation that is discretely expressed in time and space. By repeating this calculation at predetermined time intervals, the state of the flow in the exhaust manifold that changes from time to time can be described in three dimensions.

  When combining one-dimensional and three-dimensional CFD in such a manner, calculation of one-dimensional CFD is performed at the part where the flow of intake and exhaust gas is switched between one-dimensional and three-dimensional, that is, at the boundary surface on the inlet side and outlet side of the three-dimensional model. Based on the result, a boundary condition (a value of a flow variable on each boundary surface) of the three-dimensional CFD is given. However, since only the average values of the flow variables p, ρ, u, and T at the three-dimensional boundary surfaces are obtained by the calculation of the one-dimensional CFD, the details will be described later. The values of the flow variables p, ρ, u, and T for each entire boundary surface are obtained.

  Then, while delivering the calculation data in this way, the overall intake / exhaust flow is calculated using the simple one-dimensional model M1, and the part requiring particularly high accuracy (in this case, the exhaust manifold) is automatically operated. By replacing with the three-dimensional model M3, the 1 + 3-dimensional CFD simulation can be realized very easily, and while ensuring the accuracy of the analysis, the calculation amount for that is reduced and the analysis is required. Time can be shortened.

  In addition, the exhaust manifold three-dimensional model M3 can be divided into, for example, the independent intake passages s1 to s4 and the common exhaust passage s5. Therefore, instead of replacing the entire exhaust manifold with the three-dimensional model M3, for example, The independent exhaust passages for each cylinder are replaced with the three-dimensional models s1 to s4 only when the corresponding cylinders c1 to c4 are in the exhaust stroke, and the single independent exhaust passage models s1 to s4 are replaced with the common exhaust passage models. The combination with s5 is used, and this can further reduce the amount of calculation.

(Chemical reaction simulation)
As described above, the flow of the intake and exhaust of the engine is simulated by CFD. In this embodiment, the combustion state of the air-fuel mixture and combustion gas in the cylinder in the compression and expansion strokes is ignored while ignoring the motion. The chemical reaction simulation is done. Specifically, first, the state of intake air charged in the combustion chamber in the cylinder, that is, the pressure p, the density ρ, the speed u, and the temperature T is obtained by the one-dimensional or three-dimensional CFD calculation as described above. At that time, considering that the bottom dead center of the cylinder is different from the closing timing of the intake valve, the cylinder is filled by simulating the return of the intake air after flowing into the cylinder once. The state of inspiration can be obtained accurately.

  In this way, the pressure p and temperature T of the combustion chamber at the initial stage of the compression stroke are obtained, and the strength of the in-cylinder flow is obtained from the intake flow velocity u. On the other hand, the air-fuel ratio of the air-fuel mixture (or the amount of fuel supplied to the cylinder), the amount of burnt gas (internal EGR gas) remaining in the combustion chamber, the cylinder wall temperature, etc. The rotation speed, etc.). That is, in this embodiment, a map in which physical values such as the air-fuel ratio, the internal EGR gas amount, and the cylinder wall temperature are set in advance in association with the operating state of the engine is provided, and based on the operating state of the engine being simulated. A plurality of physical quantity values are read from the map.

  Then, as described above, if a plurality of physical quantity values representing the state of the combustion chamber in the initial stage of the compression stroke are obtained based on the result of the CFD calculation and the given engine operating conditions, as schematically shown in FIG. In addition, by reading a group of gas components corresponding to the set of physical quantities from the chemical reaction DB 13, the components of the working gas used for the chemical reaction simulation are appropriately reflected in the flow simulation by CFD and the engine operating conditions. Can be.

  As shown in FIG. 3, the data of the gas component group in the chemical reaction DB 13 includes various hydrocarbons mainly supplied as fuel, nitrogen and oxygen in the air, and hydrocarbons contained in the EGR gas. A representative one corresponding to a set of physical quantities representing the state of the cylinder is stored together with its reaction formula among carbon dioxide, water vapor, and the like. That is, in general, if all the chemical species related to engine combustion and their reaction formulas are listed, this is more than about 3000 types, and if all of them are to be calculated, the amount of calculation will increase significantly. This will prolong the simulation time.

  In this regard, if we focus on not only all the chemical reactions but also those that are particularly important in simulating the state of combustion, that is, typical ones that simulate combustion, it is at most tens to hundreds. Therefore, in this embodiment, only representative chemical reactions that change depending on the operating state of the engine are extracted so as to be a predetermined number (for example, 100) or less, and only representative gas components corresponding thereto are extracted. It is made to store in chemical reaction DB13. As a result, the number of gas components used in the chemical reaction simulation becomes appropriate, and the amount of calculation can be greatly reduced while ensuring the required accuracy. Further, the size of the chemical reaction DB 13 can be made moderate.

  Then, based on the gas components (chemical species) of the group extracted as described above, first, in the compression stroke of the cylinder, the pressure p of the combustion chamber rises as the piston rises, and the temperature T rises accordingly. And the reaction of each gas component under such conditions will be sequentially described in consideration of heat being taken away by heat exchange with the cylinder wall surface. By the chemical reaction simulation in the compression stroke, it is possible to reproduce the pre-flame reaction before the spark ignition is performed in the cylinder, the occurrence of preignition, and the like.

  Also, in the vicinity of the compression top dead center of the cylinder, the ignition of the air-fuel mixture by spark ignition is simulated, and the progress of the chemical reaction (combustion) is taken into account when the expansion stroke ends while taking into account the increase in the combustion chamber volume in the cylinder expansion stroke Describe sequentially. And the composition of burned gas in the cylinder obtained as a result of the chemical reaction simulation in the expansion stroke, the total calorific value and heat exchange with the cylinder wall surface, the work applied to the piston, the lowering of the piston The state of burned gas (exhaust gas) discharged from the combustion chamber when the cylinder moves to the exhaust stroke is obtained based on the expansion of the combustion chamber volume accompanying the above. This data is the initial value of the exhaust flow in the CFD program described above.

(Simulation overview)
Next, a simulation procedure by the engine performance prediction analysis system A according to this embodiment will be described. As shown schematically in FIG. 4, first, an operator performs a predetermined input operation according to a screen display or the like on any of the PC terminals 5, 5,. ) Is input (S1). This is an identification code for specifying the engine model stored in the model DB 11, an operating condition (simulated operating condition) of the engine to be simulated, and the like when the engine model has already been constructed. If is not constructed, information necessary for constructing the model is further included.

  For example, the model of the four-cylinder engine shown in FIG. 2 will be described. Geometric data representing dimensions and shapes of the engine intake and exhaust systems, combustion chambers, etc., physical data representing physical characteristics such as heat transfer coefficient thereof, or Instead of the detailed data, a code for designating engine data stored in the experiment DB 14 or the design DB 15 is input to the PC terminal 5.

  Further, for which part of the engine the three-dimensional model is used is selected, and further, in which stroke of the cylinder the three-dimensional calculation is selected for that part. That is, for example, if the purpose of analysis is to support engine exhaust system design and development, the operator selects and sets the exhaust manifold to use a three-dimensional model M3 as shown in FIG. Further, it is preferable that the independent exhaust passages s1 to s4 are set so that the three-dimensional CFD calculation is performed only when the corresponding cylinder is in the exhaust stroke.

  Subsequently, in step S2, an engine model is constructed based on the simulation data input in step S1, or is read from the model DB 11 and stored in the internal storage device (memory) of the arithmetic servers 1, 1,. Store. For example, as shown in FIG. 2A, a one-dimensional CFD model M1 extending from a part of the intake system to a part of the exhaust system, the independent exhaust passages s1 to s4 and the common exhaust for each of the cylinders c1 to c4. A three-dimensional model M3 of the exhaust manifold that can be divided into the passage s5 is stored in the memory.

  When a new three-dimensional model M3 is constructed, for example, based on the simulation data, three-dimensional design CAD data representing the shape of the exhaust manifold is read from the design DB 15 into the PC terminal 5, A model creation command attached with data designating boundary surface and mesh information is created and transmitted to the calculation servers 1, 1,. Upon receiving this command, the preprocessor is activated in the arithmetic servers 1, 1,..., And a layer mesh is pasted on the inner wall surface of the exhaust manifold passage, and the mesh is cut into the internal space.

  Alternatively, when another model creation command is transmitted from the PC terminal 5 to the calculation servers 1, 1,... Based on the initial setting data, the calculation servers 1, 1,. By reading template part data representing the basic shape of the tank and changing the dimensions and shape of the part, a three-dimensional model having a mesh for CFD calculation is constructed.

  In addition, regarding the chemical reaction simulation, a container model that defines a change in the cylinder volume with respect to a change in the crank angle, a change in heat transfer coefficient according to the cylinder wall temperature, and the like is used. This container model is a zero-dimensional physical model in the sense that there is no motion of the gas mixture or combustion gas inside.

  As described above, using the models stored in the memory of the calculation servers 1, 1,..., In step S3, a simulation calculation is performed to simulate the flow of intake and exhaust during engine operation and the state of combustion in the combustion chamber. To give an example of details of the arithmetic processing, in this embodiment, while the PC terminal 5 and the arithmetic servers 1, 1,... 1, 1,..., One-dimensional and three-dimensional CFD operations and chemical reaction simulation are executed simultaneously.

  For example, as a processing procedure of the CFD calculation, first, boundary conditions (flow variables p, ρ, u, T, etc.) and an engine operating condition at the beginning of the simulation are input to the one-dimensional CFD calculation model M1 (S31: Based on this, a one-dimensional flow characteristic equation is calculated (S32: CFD calculation). That is, in the model M1 shown in FIG. 2 (a), values of flow variables in the throttle valve thv that is the boundary on the inlet side of the flow and the catalytic converter cat that is the boundary on the outlet side are given based on the simulation data. As a result, the flow fields of the intake and exhaust gas from the downstream of the throttle valve thv to the catalytic converter cat through the combustion chambers of the cylinders c1 to c4 are obtained.

  In the subsequent step S33, the flow field data is stored, and boundary conditions of the three-dimensional CFD are given based on the data. That is, the data of the one-dimensional flow field is transferred as a data file from the calculation servers 1, 1,... To the PC terminal 5, and the PC terminal 5 that has received this data file uses the data of the one-dimensional flow field to be described later. Thus, the values of the flow variables p, ρ, u, T on the boundary surface of the three-dimensional model (in this embodiment, the inlet of any of the independent exhaust passages s1 to s4 and the outlet of the common exhaust passage s5) are obtained, and these values are obtained. An execution file of the three-dimensional CFD program included as a boundary condition is created and returned to the calculation servers 1, 1,.

  Subsequently, the calculation servers 1, 1,... That have received the execution file start a three-dimensional CFD program and set predetermined calculation conditions such as the boundary condition and engine simulation operation condition on the three-dimensional model M3 of the exhaust manifold. Input (S34: condition input), and based on this, a difference equation of a three-dimensional flow is calculated (S35: CFD calculation). That is, among the exhaust manifold model M3 shown in FIG. 2B, a three-dimensional model in which the independent exhaust passages s1 to s4 in which the corresponding cylinders are in the exhaust stroke and the common exhaust passage s5 is used. Based on the value (boundary condition) of the flow variable at the outlet (boundary surface), the state of the exhaust flowing in the passage (flow variables p, ρ, u, T), that is, the flow field of the exhaust is determined in three dimensions. Then, the three-dimensional flow field data thus obtained is stored in the memory of the arithmetic servers 1, 1,... (S36: data storage).

  Of the flow field data at the beginning of the simulation thus obtained in 1 + 3 dimensions, for example, the data related to combustion in the cylinder and the state of burned gas discharged from the cylinder will be described later. The data is rewritten based on the result of the chemical reaction simulation (data conversion, provision and rewriting: S37). Thereafter, the crank angle of the engine is advanced by a minute crank angle (time increment) set in advance (increment: S38), and it is determined whether or not the crank angle position set as the end of the simulation is reached (S39). If so, the process returns to step S31, and the one-dimensional and three-dimensional CFD calculations (S31 to S36) are repeatedly executed for each minute crank angle.

  In this way, 1 + 3 dimensional CFD calculation is repeatedly performed for each minute crank angle from the beginning to the end of the simulation, so that the flow of the intake / exhaust flow field of the engine changes from moment to moment in time series. Are stored in the internal storage of the calculation servers 1, 1,.

  As described above, the operating conditions included in the simulation data (step S1) are substantially constant when simulating the steady operating state of the engine. At this time, the flow of the intake air flow in the throttle valve thv of the one-dimensional CFD model M1 The variables p, ρ, u, and T are substantially constant. On the other hand, when simulating an unsteady driving state in which the driving state changes, the simulation data includes time-series simulated driving conditions representing the driving state changing in such a manner, and steps S31 and S34 in the flow. Then, an operating condition that varies according to a change in the crank angle is given.

  In parallel with the above-described 1 + 3-dimensional CFD calculation, the calculation of the chemical reaction simulation (chemical reaction SIM) is performed for each cylinder in the compression stroke and the expansion stroke. That is, when one of the cylinders (hereinafter, for example, described as the first cylinder c1) shifts from the intake stroke to the compression stroke as the simulation progresses, the CFD calculation described above is performed as schematically shown in FIG. Calculation result data is transmitted from the calculation servers 1, 1,... To the PC terminal 5. The PC terminal 5 that has received this data obtains the pressure p, temperature T, etc. of the intake air charged in the first cylinder c1 and the ratio of EGR gas in the intake air based on the data, and determines the current operating conditions of the engine. Based on this, the values of physical quantities such as air-fuel ratio and cylinder wall temperature are read from the map, a set of physical quantities representing the state in the cylinder is specified, and a chemical reaction simulation program including an identification code corresponding to the set of physical quantities is executed The file is transmitted to the arithmetic servers 1, 1,... (Data exchange between the programs is shown as result processing * 1 in the figure).

  Upon receiving the execution file, a chemical reaction simulation program is started in the arithmetic servers 1, 1,..., And as shown in the flow of FIG. 4, group data of gas components corresponding to a set of physical quantities of the identification code is stored in the chemical reaction DB 13. (S41: reading of chemical species), and describes the chemical reaction of the gas component at a preset small crank angle (time increment) while simulating the expansion of the combustion chamber volume by the container model of the first cylinder c1. (S42: Chemical reaction calculation), and the result is stored (S43: Data storage). Such calculation of the chemical reaction formula is repeatedly performed for each minute crank angle from the initial stage of the compression stroke to the end of the expansion stroke of the cylinder c1, and thereby the compression and expansion strokes in the combustion chamber in the cylinder c1. Data describing the state of the working gas in chronological order is stored in the storage device as a result of the chemical reaction calculation.

  When the first cylinder c1 finishes the expansion stroke and shifts to the exhaust stroke, the chemical reaction simulation for the cylinder c1 is finished, and as shown in FIG. Data such as the composition of burned gas (exhaust gas) discharged from the combustion chamber, the heat generated by combustion, and the work amount are transmitted from the calculation servers 1, 1,. In the PC terminal 5 receiving this data, the initial state of the exhaust flow blown out from the cylinder based on the composition of the burned gas (exhaust gas) discharged from the combustion chamber of the first cylinder c1, the heat generated by the combustion, the work amount, etc. , P, ρ, u, and T are obtained, and a data file of this variable and a predetermined command for rewriting the operation result data of the CFD operation based on the data file are created, and the operation servers 1, 1,. Return to

  Then, the calculation servers 1, 1,... That have received the command and the file are portions of the compression stroke and expansion stroke of the first cylinder c1 in the calculation result data of the one-dimensional CFD calculation in step S37 of the flow of FIG. Will be rewritten. Further, in consideration of EGR, the data of the gas component in the chemical reaction DB 13 is corrected based on the composition of the exhaust gas.

  As described above, in step S3 of the main program, the 1 + 3-dimensional CFD calculation and the chemical reaction simulation calculation are performed in parallel in synchronization with the change of the crank angle of the engine from the start to the end of the simulation. When the crank angle position set as the end of the simulation is reached (determination is YES in S39), the process proceeds to step S4, the simulation result is output, and then the control ends (end).

  As the output of the simulation result in the step S4, the necessary data is read out from the data of the time series calculation results stored in the storage device of the calculation servers 1, 1,... And transferred to the PC terminal 5, Based on this data, a predetermined evaluation value relating to engine performance may be output. For example, the output characteristics of the engine, the fuel consumption characteristics, the change in volumetric efficiency of each cylinder accompanying the change in the engine operating state, etc. may be graphed and displayed on the display of the server 1, 1,. In addition, for example, the result of the three-dimensional CFD calculation regarding the flow of exhaust gas in the exhaust manifold may be visualized and displayed as an image.

  Step S32 of the flow shown in FIG. 4 corresponds to a first CFD calculation step of calculating the flow field of intake and exhaust of the engine by executing a one-dimensional CFD program, and similarly, step S35 is a three-dimensional CFD program. To correspond to the second CFD calculation step of calculating the flow field of intake and exhaust.

  In the prediction analysis system A of this embodiment, the calculation servers 1, 1,... Are executed in the calculation servers 1, 1,. A first CFD computing unit 1a that executes a program and a second CFD computing unit 1b that executes a three-dimensional CFD program are configured.

(How to give boundary conditions for 3D CFD)
As described above, in step S33 of the main program, from the result of the one-dimensional CFD calculation, the inlet-side and outlet-side boundary surfaces of the three-dimensional model (for example, the inlets and common exhaust passages of the independent exhaust passages s1 to s4 of any one of the exhaust manifolds) The values of the flow variables p, ρ, u, and T at the outlet of s5 are obtained. In this case, for example, FIG. 6 (a) schematically illustrates the independent exhaust passage s1 inlet of the first cylinder, for example. As shown in FIG. 4, it is considered that the flow is substantially uniform on the boundary surface and there is no deviation, and the value of the flow variable obtained by the one-dimensional CFD calculation is directly developed on the entire boundary surface.

  However, in general, the flow of intake and exhaust shows a flow velocity distribution as shown in (b) and (c) of the figure even if the passage is straight, and the flow velocity is relatively low near the passage wall due to viscosity. The further away from the wall, the higher the flow velocity. In addition, the flow velocity distribution varies greatly depending on the flow state, and in the laminar flow state where the flow is relatively slow, a velocity gradient appears only in the boundary layer adjacent to the wall surface as shown in Fig. 2 (b), and is almost constant otherwise. In the turbulent state where the flow is relatively fast, a velocity gradient appears over substantially the entire cross section of the passage as shown in FIG. Further, when the passage is curved in the vicinity of the inlet side boundary surface as in the independent exhaust passage s1, the flow of the outer portion tends to be faster than the curved inner portion (FIG. 8 ( a)).

  Therefore, as described above, when a flow variable is developed almost uniformly over the entire three-dimensional boundary surface as a boundary condition (FIG. 6 (a)), the vicinity of the boundary surface In particular, in the example of the figure, in the vicinity of the curved inner wall surface of the passage indicated by symbol D, the flow velocity value given as the boundary condition becomes considerably larger than the downstream flow velocity value obtained by the three-dimensional CFD calculation. Since the deviation of the flow velocity value between adjacent meshes becomes excessively large, there is a possibility that the calculation may diverge.

  Therefore, in this embodiment, as a characteristic part of the present invention, first, the flow bias distribution at the inlet side and outlet side boundary surfaces of the three-dimensional model used for the analysis is examined in advance, and this is used as the flow bias distribution data for CFD calculation. When the values of the flow variables p, ρ, u, and T (boundary conditions) at the three-dimensional boundary surfaces are obtained from the result of the one-dimensional CFD calculation as described above, the flow at the boundary surfaces is stored. The average value of the variables was weighted according to the flow bias distribution and developed over the entire boundary surface.

-Influence of passage shape including boundary surface-
For example, the flow velocity will be described as the flow distribution data. First, as shown in FIGS. 7A to 7C, the flow near the center of gravity G according to the shape of the boundary surface of the three-dimensional CFD model. A basic bias distribution pattern in which the flow unevenness is distributed in layers (hierarchically) is set so as to be relatively fast and relatively slow near the passage wall. Further, the velocity gradient between the layers of the bias distribution pattern is set separately for the laminar flow state and the turbulent flow state as shown in FIGS. 6 (b) and 6 (c).

  Further, the influence of the curved shape of the intake / exhaust passage including the boundary surface is incorporated. That is, for example, when the passage is curved in the vicinity of the inlet side boundary surface as in the independent exhaust passage s1, and the distance between the boundary surface and the passage wall surface facing the boundary surface is very close, as shown in FIG. As described above, the flow is bent along the wall surface of the passage, so that the flow on the curved inner side becomes slightly slower at the upstream side boundary surface, and the flow on the outer side becomes faster. Therefore, as shown in the drawing, the fastest flow portion on the inlet side boundary surface is shifted from the center of gravity position Gin to the outside of the curved path.

Specifically, for example, as shown in the figure, a local orthogonal coordinate system having a center of gravity Gin of the entrance side boundary surface as an origin and an X, Y axis orthogonal to each other in the boundary surface and a Z axis orthogonal to the boundary surface. , The passage shape dependence coefficient αin in the vicinity of the inlet is defined by the distance L between the boundary surface and the passage wall surface facing the Z-axis direction, thereby determining the amount of deviation from the center of gravity position Gin of the flow center. To do. As an example of the coefficient αin, as shown in FIG. 8 (b), the distance L and the representative length D of the inlet side boundary surface (for example, the equivalent diameter of the boundary surface),
αin = 1 (however, 0 <L / D ≦ 1)
αin = D / L (where 1 <L / D ≦ 4)
αin = 0 (4 <L / D)
(The concept of obtaining the deviation amount by the coefficient αin is the same as that on the outlet side below).

  On the other hand, it is necessary to consider the curved shape of the entire passage on the exit side boundary surface. That is, for example, as shown in FIG. 9 (a), when the first cylinder is in the exhaust stroke, the exhaust flowing into the independent exhaust passage s1 from the inlet is largely curved along the shape of the passage, and then the continuous common exhaust passage s5. When the flow of exhaust gas is greatly curved and flows from the left side to the right side as shown in the figure, the flow is also biased to the right side of the drawing on the outlet side boundary surface. Because it will be.

  Therefore, for example, as shown in FIGS. 9B and 10A, the center of gravity Gout of the exit side boundary surface is set as the origin, and the X and Y axes orthogonal to each other in the boundary surface are orthogonal to the boundary surface. In the local orthogonal coordinate system composed of the Z-axis, the deviation amount M of the entrance-side boundary surface centroid position Gin projected onto the XY plane with respect to the exit-side centroid Gout (origin), and the representative length H of the exit-side boundary surface (For example, equivalent diameter) defines a correction coefficient β for reflecting the degree of curvature of the entire passage in the flow deviation.

More specifically, if the center-of-gravity position coordinates of the entrance-side boundary surface in the local orthogonal coordinate system on the exit side are X1 and Y1, the deviation amount M = √ (X1 ² + Y1 ² ). At this time, the correction coefficient β is, for example,
β = 0.2 × (M / H) ² −0.1 × (M / H) +1 (where M / H ≦ 2)
β = 2 (where M / H> 2)
Can be defined as

Further, even if the relationship between the gravity center positions Gin and Gout of the inlet and the outlet is the same, if the shape of the passage near the outlet is greatly different as shown by the solid line and the broken line in FIG. Since the flow unevenness on the surface is different, the passage shape dependence coefficient αout in the vicinity of the outlet is determined from the passage wall surface facing the center of gravity (origin) of the boundary surface on the outlet side in the local orthogonal coordinate system on the outlet side. Depending on the distance L to
αout = 2 (however, 0 <L / D ≦ 1)
αout = H / L (where 1 <L / D ≦ 4)
αout = 1 (However, 4 <L / D)
It is defined as

  Then, the coefficient αout and the correction coefficient β define a deviation coefficient γ representing how much the flow center position is deviated from the boundary surface gravity center Gout on the outlet side boundary surface as γ = αout × β. As shown schematically in FIG. 10 (b), the above-mentioned basic bias distribution pattern (see FIG. 7) is corrected to thereby distribute the flow bias distribution on the outlet side boundary surface reflecting the influence of the curved shape of the passage. Can be requested.

  That is, first, as shown in FIG. 10 (a), a vector V1 (X1, Y1) of a deviation direction is obtained from the center-of-gravity position coordinates (X1, Y1) of the entrance side boundary surface in the local orthogonal coordinate system on the exit side. The direction of deviation of the flow center at the outlet side boundary surface is determined by the unit inverse vector V2. Then, from the deviation coefficient γ, a deviation amount T = {(γ−1) / 12} × H is obtained, and the center of the flow is shifted from the center of gravity Gout to the deviation direction V2 as shown in FIG. It is only necessary to move by the amount T to obtain a flow uneven distribution pattern.

-Effects of flow conditions-
As described above, the flow distribution distribution pattern at each boundary surface is determined by incorporating the influence of the passage shape, and the rate of change in flow velocity and pressure between the layers of this pattern is the flow state, that is, laminar flow. Set separately depending on whether the state is turbulent or turbulent. That is, for example, in the independent exhaust passage s1, when the corresponding first cylinder is in the intake to expansion stroke, and when the first cylinder is in the exhaust stroke and blows out high-temperature and high-pressure burned gas, The flow rates are quite different, and such a significant change in flow rate is repeated for each combustion cycle of the cylinder, and each time the flow state transitions between a laminar flow state and a turbulent flow state.

  In addition, if the exhaust temperature changes due to changes in engine operating conditions (rotation speed, load, ignition timing, warm / cold, etc.), this will change the exhaust density and viscosity. The point at which the state transitions between laminar and turbulent flows changes.

  Therefore, in this embodiment, as described above, the deviation distribution of the flow at each boundary surface is set separately for the laminar flow state and the turbulent flow state, and as described above, the 1 + 3-dimensional simulation that simulates the engine operating state is performed. When performing the CFD calculation (see FIG. 4 etc.), the Reynolds number Re of the flow is calculated based on the average flow variable of each boundary surface obtained by the one-dimensional CFD calculation. Or the turbulent flow state, the flow distribution distribution at each boundary surface is obtained by referring to the distribution data.

  As such, considering the shape of the boundary surface on the inlet side and the outlet side of the three-dimensional CFD model, the curved shape of the intake and exhaust passages, and the flow state, the deviation of the flow at each boundary surface from the result of the one-dimensional CFD calculation If the distribution is obtained and the value of the flow variable developed on the three-dimensional boundary surface is given as a boundary condition to the three-dimensional CFD calculation, the flow variable value on the boundary surface and the boundary surface calculated in three dimensions Nearby variable values will not be too different.

  Next, a specific procedure for providing a three-dimensional CFD boundary condition from the result of the one-dimensional CFD operation as described above will be described with reference to the flowchart of FIG. The procedure of this flow is performed in the CFD calculation of the main flow shown in FIG. 4, particularly in step S33, and the flow field data of the one-dimensional CFD calculated in step S32 of the main flow is the calculation server 1, .., And when transferred to the PC terminals 5, 5,..., The subsequent steps are received by the PC terminals 5, 5,. In S331, the Reynolds number Re of the flow at the inlet side and outlet side boundary surfaces is calculated from the flow field data, and is compared with the critical Reynolds number Rc to determine whether the flow is in a laminar state or a turbulent state. To do.

  Subsequently, in step S332, with reference to the bias distribution data of the CFD calculation DB 12, a basic flow bias distribution at each boundary surface, that is, a flow variable p such as a hierarchical distribution pattern and a velocity gradient between the hierarchies. , Ρ, u, T values are read, and in accordance with this distribution data, the one-dimensional flow variables p, ρ, u, T are developed with appropriate weights over the entire three-dimensional boundary surface in step S333. . The execution file including the boundary condition of the three-dimensional CFD thus obtained is returned to the calculation servers 1, 1,... In the subsequent step S334, and the control ends (END).

  In the arithmetic servers 1, 1,... That have received the executable files returned in this way, the three-dimensional CFD program is started as described in the main flow of FIG. 4, and the arithmetic conditions including the boundary conditions are included in the three-dimensional CFD model. (S34), and based on this, a three-dimensional CFD calculation is performed (S35). In this three-dimensional CFD calculation, an appropriate boundary condition is given as described above. Therefore, the deviation of the flow variable between the meshes does not become excessively large near the boundary surface, and the system down due to the divergence of the calculation can be prevented.

  Steps S331 and S332 in the flow of FIG. 11 show the distribution of the intake and exhaust flow unevenness at the inlet and outlet interfaces of the three-dimensional CFD model in advance, the shape of the boundary, the curved shape of the intake and exhaust passages, the flow state, and the like. This corresponds to the bias distribution setting step to be set by reading from the bias distribution data (DB12) set in association with.

  In step S333, based on the flow field data obtained by the one-dimensional CFD calculation, the flow variables p, ρ of the entire boundary surfaces are determined according to the flow distribution set in the distribution distribution setting steps S331 and S332. , U, and T values are obtained, and this corresponds to a boundary condition applying step in which these are used as boundary conditions for the three-dimensional CFD calculation.

  In the predictive analysis system A of this embodiment, the PC terminals 5, 5,... Are three-dimensionally executed by executing steps S331, S332 and S333 of the flow in the PC terminals 5, 5,. Boundary conditions for three-dimensional CFD calculation based on bias distribution setting means 5a for setting the bias distribution of intake and exhaust flows at the inlet and outlet side boundary surfaces of the CFD model and flow field data calculated by the first CFD calculation means 1a Boundary condition providing means 5b for providing

(Function and effect)
Therefore, according to the engine performance prediction analysis system A according to this embodiment, when analyzing the flow of the intake and exhaust of the engine by the application of CFD, a one-dimensional engine model M1 is basically used. While performing the CFD calculation, the three-dimensional calculation is performed on the preselected part using the three-dimensional model M3, s1 to s5 under the boundary condition given by the one-dimensional CFD calculation. Therefore, performance characteristics such as engine output and fuel consumption can be predicted with sufficiently high accuracy, and the amount of calculation for that purpose can be greatly reduced, and the time required for analysis can be shortened.

  Further, as described above, when the value of the flow variable (boundary condition) on the boundary surface of the three-dimensional model is obtained from the data of the one-dimensional flow field, the influence of the shape of the boundary surface and the curved shape of the intake and exhaust passages is affected. Since the one-dimensional flow variable value is developed over the entire three-dimensional boundary surface according to the appropriate bias distribution data woven in, the value of the flow variable calculated in three dimensions is between the meshes near the boundary surface. As a result, the three-dimensional CFD as a whole is operated with high accuracy using a high-order scheme, and the time is shortened by calculating in a relatively coarse time step. At the same time, the system can be prevented from being down due to the divergence of calculation.

  Further, in this embodiment, the flow velocity of the intake / exhaust partly changes greatly during the operation of the engine, and as the flow state repeatedly transitions between the laminar flow state and the turbulent flow state, Considering that the distribution itself changes greatly, it is determined from the flow variable value obtained by the one-dimensional CFD calculation whether the flow is in a laminar flow state or a turbulent flow state, and the flow bias distribution is determined accordingly. Since the change is made, the above-described effects can be obtained even when a portion where the flow velocity changes extremely, such as an independent exhaust passage of an exhaust manifold, is simulated in three dimensions.

  In addition, in this embodiment, data in which an appropriate flow bias distribution is set for each boundary surface of the three-dimensional model as described above is stored in the CFD calculation DB 12, and the DB 12 is stored in the middle of the 1 + 3D simulation. By referencing, since the appropriate boundary conditions as described above are automatically assigned, the utility as a design / development support tool is extremely high.

(Other embodiments)
In addition, this invention is not limited to the said embodiment, Other various embodiment is included. That is, in the above-described embodiment, for each boundary surface of the physical model M3, s1 to s5 for the three-dimensional CFD, an appropriate flow bias distribution reflecting the shape and the degree of curvature of the passage is represented by the flow state ( Although it is separately set in the DB 12 in association with (laminar flow / turbulent flow), for example, a basic bias distribution pattern corresponding to the boundary surface shape as shown in FIG. A pattern or calculation formula for the degree of bias corresponding to the flow state as shown in b) and (c), and a calculation formula for reflecting the curved shape of the intake and exhaust passages in the flow bias distribution are set in advance. These may be combined as appropriate to obtain the flow uneven distribution for each boundary surface.

  Alternatively, instead of separately setting the flow uneven distribution at each boundary surface in association with the flow state (laminar flow / turbulent flow), it is set in association with the engine simulation operation condition instead. You can also.

  In the above embodiment, the case where the three-dimensional CFD calculation is performed on the exhaust manifold of the engine has been described. However, the present invention is not limited to this. For example, the shape of the intake system surge tank, the entire intake port, and the intake air facing the combustion chamber The present invention can also be applied to a case where the shape near the port opening is simulated in three dimensions.

  Furthermore, in the above-described embodiment, the chemical reaction simulation is performed for the compression and expansion strokes of each cylinder. However, this is not performed, and the flow of the intake and exhaust of the engine is simulated only by one-dimensional and three-dimensional CFD. You may make it do.

  Moreover, although the said embodiment demonstrated the case where the simulation about a 4-cycle engine was performed, it cannot be overemphasized that a 2-cycle engine and a rotary engine can also be simulated.

  As described above, the system for predicting and analyzing engine performance according to the present invention reduces the calculation time while sufficiently increasing the accuracy of predicting the engine performance by high-precision CFD calculation, and the system down resulting from it. Therefore, it has sufficient practicality as a design / development support tool, and is particularly suitable for the design / development of automobile engines.

1 is an overall configuration diagram of an engine performance prediction analysis system A according to an embodiment of the present invention. It is a schematic diagram which shows an example of the physical model for CFD calculation. It is explanatory drawing which shows a response | compatibility with the group of the physical quantity showing the state in a cylinder, and the group data of the gas component in chemical reaction DB. It is a main flowchart which shows the outline of the procedure of simulation. It is explanatory drawing which shows typically switching of CFD and chemical reaction simulation, and transmission / reception of the data accompanying this. (a) is the exhaust flow velocity distribution when the flow is considered to be substantially uniform at the inlet side boundary surface of the independent exhaust passage, and (b) and (c) are general flow velocity distributions in the pipeline. . It is explanatory drawing of the basic deviation distribution pattern of the flow according to the shape of a boundary surface. FIG. 6A is a graph corresponding to FIG. 6A when an appropriate bias distribution is given, and FIG. 6B is a graph showing an example of the inlet-side channel shape dependency coefficient. It is explanatory drawing which shows the deviation of the flow of the exit side boundary surface resulting from the curve of an exhaust passage, and (b) the exit side local orthogonal coordinate for calculating | requiring it. (a) is explanatory drawing which shows an example of the method of calculating | requiring the bias | inclination of the flow in an exit side interface, (b) is an image figure which shifts the center position of a flow according to it. It is a flowchart which shows the boundary condition provision procedure of three-dimensional CFD.

Explanation of symbols

A Engine performance prediction analysis system M1 One-dimensional CFD analysis model M3, s1 to s5 Three-dimensional CFD analysis model Gin, Gout Boundary surface centroids 1, 1, ... Calculation server 1a First CFD calculation means 1b Second CFD calculation means 5, 5, ... PC terminal 5a Bias distribution setting means 5b Boundary condition giving means

Claims (15)

A one-dimensional CFD program for simulating an intake / exhaust flow from at least a part of the intake system to a part of the exhaust system of the engine using a one-dimensional CFD analysis model;
A three-dimensional CFD program for simulating an intake / exhaust flow in a predetermined part of the intake system or the exhaust system using a three-dimensional CFD analysis model;
A data exchange program for providing boundary conditions for computation by the three-dimensional CFD program based on at least flow field data computed by the one-dimensional CFD program;
A predictive analysis method for analyzing the flow of intake and exhaust by causing each program to be executed in parallel by a computer device, thereby predicting engine performance,
The distribution distribution of the intake and exhaust flow at the inlet side and outlet side boundary surfaces of the three-dimensional CFD analysis model is set in advance as a database in association with at least the shape of each boundary surface,
Based on the flow field data obtained by the one-dimensional CFD calculation, the flow variable value of each boundary surface is obtained according to the flow distribution of each boundary surface set in the database, and this value is calculated by the three-dimensional CFD calculation. A method for predicting and analyzing engine performance, characterized by using boundary conditions. 1-dimensional and 3-dimensional CFD programs for simulating the flow of engine intake and exhaust using 1-dimensional and 3-dimensional CFD analysis models, respectively, are executed in parallel, and at least the intake system This is a prediction analysis system that analyzes the flow of intake and exhaust air from a part of the exhaust system to a part of the exhaust system, thereby predicting the performance of the engine,
First CFD calculation means for calculating a flow field of intake / exhaust gas from at least a part of the intake system to a part of the exhaust system using the one-dimensional CFD analysis model;
Boundary condition giving means for giving a boundary condition for CFD calculation by the three-dimensional CFD program based on the flow field data calculated by the first CFD calculation means;
Second CFD calculation means for executing the three-dimensional CFD program based on the boundary condition given by the boundary condition giving means;
Bias distribution setting means for setting the bias distribution of the intake and exhaust flows at the inlet side and outlet side boundary surfaces of the three-dimensional CFD analysis model based on at least the shape of the boundary surfaces;
Based on the flow field data calculated by the first CFD calculating means, the boundary condition applying means is adapted to the flow variable of the entire boundary surface in accordance with the flow distribution distribution of each boundary face set by the bias distribution setting means. A system for predicting and analyzing engine performance, characterized in that the value of the above is obtained and used as a boundary condition for three-dimensional CFD calculation.   The bias distribution setting means distributes the flow rate of intake and exhaust air in a layered manner so that the flow is relatively fast near the center of gravity of each boundary surface, but is relatively slow near the passage wall. The prediction analysis system according to claim 2.   When the intake / exhaust passage simulated by the analysis model is curved in the vicinity of the inlet side boundary surface, the bias distribution setting means shifts the fastest part of the flow at the inlet side boundary surface to the outside of the passage curve. The predictive analysis system according to claim 3.   When the intake / exhaust passage simulated by the analysis model is curved, the bias distribution setting means reflects the flow deviation generated on the outlet side boundary surface in the flow distribution distribution on the outlet side boundary surface. The prediction analysis system according to claim 3, wherein   The bias distribution setting means determines whether the flow at each boundary surface is a laminar flow state or a turbulent flow state based on the flow field data calculated by the first CFD calculation means, and the flow distribution is determined according to the determination result. 6. The predictive analysis system according to claim 2, wherein the bias distribution is changed and set. A database in which the uneven distribution of the intake and exhaust flows at each boundary surface is associated with at least the shape of each boundary surface, and is set separately when the flow is in a laminar flow state and when in a turbulent flow state,
The bias distribution setting means reads and sets the flow bias distribution corresponding to the flow state at each boundary surface from the database based on the flow field data calculated by the first CFD calculation means. The predictive analysis system according to claim 6, wherein the system is predictive analysis. A database in which the uneven distribution of the intake and exhaust flows at each boundary surface is set in association with at least the shape of each boundary surface and the simulated operating conditions of the engine,
6. The prediction analysis system according to claim 2, wherein the bias distribution setting means reads and sets a flow bias distribution corresponding to the simulated operation condition from the database. 1-dimensional and 3-dimensional CFD programs for simulating the flow of engine intake and exhaust using 1-dimensional and 3-dimensional CFD analysis models, respectively, are executed in parallel, and at least the intake system A control program for a predictive analysis system that analyzes the flow of intake and exhaust air from a part of the exhaust system to a part of the exhaust system and thereby predicts the engine performance,
A first CFD calculation step of calculating a flow field of intake and exhaust gas from at least a part of the intake system to a part of the exhaust system using the one-dimensional CFD analysis model;
A boundary condition providing step for providing a boundary condition for CFD calculation by the three-dimensional CFD program based on the flow field data calculated in the first CFD calculation step;
A second CFD calculation step of executing the three-dimensional CFD program based on the boundary condition given in the boundary condition applying step;
A bias distribution setting step for setting the bias distribution of the intake and exhaust flows at the inlet and outlet boundary surfaces of the three-dimensional CFD analysis model based on at least the shape of the boundary surface;
In the boundary condition applying step, the flow variables of the entire boundary surface are determined according to the flow distribution of each boundary surface set in the bias distribution setting step based on the flow field data calculated in the first CFD calculating step. A control program for an engine performance prediction analysis system, characterized in that a value is obtained and used as a boundary condition for a three-dimensional CFD calculation.   The flow distribution of the intake and exhaust air is distributed in a layered manner so that the flow is relatively fast near the center of gravity of each boundary surface and is relatively slow near the passage wall in the bias distribution setting step. 9 control programs.   In the bias distribution setting step, when the intake / exhaust passage simulated by the analysis model is curved in the vicinity of the inlet side boundary surface, the fastest part of the flow in the inlet side boundary surface is shifted outside the curved portion of the passage. The control program according to claim 10.   In the bias distribution setting step, when the intake / exhaust passage simulated by the analysis model is curved, the flow deviation generated at the outlet side boundary surface is reflected in the flow bias distribution on the outlet side boundary surface. The control program according to claim 10.   In the bias distribution setting step, it is determined whether the flow at each boundary surface is a laminar flow state or a turbulent flow state based on the flow field data calculated in the first CFD calculation step, and the flow is determined according to the determination result. 13. The control program according to claim 9, wherein the bias distribution is changed and set. The predictive analysis system associates the distribution of bias of the intake and exhaust flows at each boundary surface of the three-dimensional CFD analysis model with at least the shape of each boundary surface, and when the flow is in a laminar flow state and a turbulent flow state. With a database set up separately in
In the bias distribution setting step, based on the flow field data calculated in the first CFD calculation step, a flow bias distribution corresponding to the flow state at each boundary surface is read from the database and set. The control program according to claim 13. A database in which the uneven distribution of the intake and exhaust flows at each boundary surface is set in association with at least the shape of each boundary surface and the simulated operating conditions of the engine,
The control program according to any one of claims 9 to 12, wherein in the bias distribution setting step, a flow bias distribution corresponding to the simulated operation condition is read from the database and set.

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