JP2006284214A - Thermal analyzing method and its program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal analyzing method for performing the thermal analysis of the inside of matter in a short time in consideration of the effect of the fluid flowing through the periphery of the matter while ensuring sufficient precision, and its program. <P>SOLUTION: The division of a target region for dividing the matter into a finite number of elements is performed and the wall boundary condition in the calculation of the matter is adapted to the division result of the target region to perform the thermal analysis of the inside of the matter. This thermal analyzing method includes first procedure for calculating the behavior of the cooling fluid flowing through the periphery of the matter to calculate the flow velocity and turbulent flow component of the cooling fluid, second procedure for calculating the heat conductivity in the heat conduction boundary of the outer wall of the matter with the cooling fluid on the basis of the flow velocity and turbulent flow component of the cooling fluid and third procedure for utilizing the calculated heat conductivity to perform the thermal analysis of the inside of the matter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermal analysis method and a program thereof, and more particularly, to a thermal analysis method and a program thereof suitable for thermal analysis inside an object considering the influence of a fluid flowing around the object.

As a technique for performing thermal analysis inside an object, Patent Document 1 discloses a heat transfer boundary surface where heat transfer occurs and boundary conditions between an inner wall surface of an engine block (the surface of a cylinder block or a cylinder head) and in-cylinder gas. The heat transfer coefficient corresponding to the heat input and output heat at the boundary surface is set, and the thermal analysis is performed using the temperature of the virtual heat transfer boundary surface and the heat transfer coefficient, and the deviation between the analysis result and the target value is A technique for repeating thermal analysis until it falls within the reference range is disclosed.
JP 2003-42984 A

  When performing thermal analysis in a steady state inside an object, it is only necessary to perform thermal analysis only inside the object. FIG. 5 is a diagram showing a procedure for analyzing only the combustion change in the steady state of the engine. In step S51, conditions such as the temperature of the heat transfer boundary surface are input as measured values or assumed values together with various initial conditions. . In step S52, the thermal boundary condition of the engine block inner wall is set from the input initial conditions. In step S53, in-cylinder gas flow analysis and combustion analysis are executed using the set thermal boundary condition, and in step S54, the thermal analysis result is output.

  However, when there is a fluid that flows outside the object, it is necessary to perform a thermal analysis inside the object in consideration of the thermal effect of the fluid flow on the object. Even in this case, if a coupled calculation between the flow analysis outside the object and the heat analysis inside the object is performed, it is theoretically possible to perform a heat analysis inside the object considering the flow of the fluid outside the object.

  FIG. 6 is a flowchart showing a procedure for performing combustion analysis by performing three thermal coupling calculations of in-cylinder gas, engine block and cooling fluid, and setting boundary conditions between the inner wall surface of the engine block and in-cylinder gas Furthermore, the boundary condition between the outer wall of the engine block and the cooling fluid must be set, and the thermal analysis must be repeated until the deviation between the thermal analysis result and the target value falls within the reference range at each heat transfer boundary. . Therefore, there has been a technical problem that the calculation amount becomes enormous and it takes a long time for the convergence calculation.

  The object of the present invention is to solve the above-mentioned problems of the prior art, and to perform a thermal analysis inside the object in consideration of the influence of the fluid flowing around the object in a short time while ensuring sufficient accuracy, and its To provide a program.

In order to achieve the above-described object, the present invention performs target area division to divide an object into a finite number of elements, and applies the wall boundary condition of the heat conduction calculation of the object to the target area division result. The thermal analysis method for performing thermal analysis inside the object is characterized in that the following measures are taken.
(1) The first procedure for calculating the flow velocity and turbulence component of the cooling fluid flowing around the object, the heat transfer coefficient at the heat transfer boundary between the outer wall of the object and the cooling fluid, The method includes a second procedure for calculating based on a flow velocity and a turbulent component of the cooling fluid, and a third procedure for performing a thermal analysis inside the object using the calculated heat transfer coefficient.
(2) the object is an engine block in which a combustion chamber is formed; a fourth procedure for updating a thermal boundary condition of the inner and outer walls of the engine block; a fifth procedure for performing combustion gas flow and combustion calculation; A sixth procedure for updating a boundary condition of the inner wall of the engine block based on the calculation result; and a seventh procedure for repeating the fourth to sixth procedures until the boundary condition converges. Features.
(3) The cooling fluid behavior calculation includes a momentum conservation equation calculation, a pressure equation calculation, and a turbulence model calculation, and does not include an energy conservation equation calculation.
(4) In the first procedure, the behavior calculation of the cooling fluid is performed with respect to an arbitrary plurality of vehicle speeds, and in the second procedure, the heat transfer coefficient at the heat transfer boundary between the outer wall of the object and the cooling fluid is It is calculated for each vehicle speed at a plurality of points, and further, based on the heat transfer coefficient calculated for each vehicle speed, the heat transfer coefficient at vehicle speeds other than the plurality of points is interpolated.
(5) A thermal analysis program for causing a computer to execute the thermal analysis method according to any one of claims 1 to 4.

According to the present invention, the following effects are achieved.
(1) According to the first and fifth aspects of the invention, the influence of the fluid flowing around the object on the inside of the object can be used as a fixed heat transfer coefficient for the thermal analysis inside the object. It is not necessary to perform a convergence calculation by simultaneously analyzing the fluid during the internal thermal analysis. Therefore, by omitting the convergence calculation, the thermal analysis inside the object can be performed in a short time.
(2) According to the invention of claim 2, the flow calculation of the fluid outside the object is continuously performed even in the case of thermal analysis that has a combustion chamber inside like an engine block and requires combustion analysis inside the object. Therefore, it is possible to quickly analyze the heat in the combustion chamber in consideration of cooling of the fluid flowing around the engine block.
(3) According to the invention of claim 3, calculation of the behavior of the cooling fluid is simplified because the calculation of the energy equation is not required in the calculation of the behavior of the cooling fluid.
(4) According to the invention of claim 4, the flow calculation around the object can be completed only by performing the heat transfer calculation at several vehicle speeds.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a main part of a thermal analysis apparatus according to the present invention, and an input device 1 including a keyboard, a mouse, a jog dial, etc. for inputting an initial value of a heat transfer coefficient, a temperature at a specific point, and the like. The analysis unit 2 that performs thermal analysis by executing various function calculations, the display unit 3 that outputs the thermal analysis result, and the three-dimensional model or finite element division model as the shape data of the object to be analyzed The stored file system 4 is the main component.

  FIG. 7 is a functional block diagram of the thermal analysis device, a shape data output unit 31 that outputs shape data of an object to be analyzed, and a heat transfer rate calculation unit that calculates a heat transfer coefficient based on the shape data. 32, a heat conduction analysis unit 33 that reads shape data from the shape data output unit 31 and further reads a heat transfer coefficient from the heat transfer coefficient calculation unit 32 to perform heat transfer analysis, and is obtained as a result of the heat transfer analysis. And a temperature distribution output unit 34 for displaying the temperature distribution. The heat transfer coefficient calculation unit 32 includes a function 32a for calculating fluid behavior and a function 32b for calculating a heat transfer coefficient based on the analysis result.

  FIG. 8 is a block diagram showing the configuration of the main part of the engine 10 to be analyzed in the present embodiment. The engine block 11, the piston 12 that moves up and down inside the engine block 11, and the up and down movement of the piston 12 are shown. And a crank mechanism 13 that converts it into rotational motion, and the volume of the combustion chamber 14 changes according to the position of the piston 12. A fluid flows around the engine block 11.

  In FIG. 1, the analysis unit 2 creates a three-dimensional model of an engine, performs a region division (mesh cutting) of the three-dimensional model for FEM analysis, and creates a finite element, and an engine block A heat transfer coefficient calculator 21 for calculating a heat transfer coefficient distribution αn (α1, α2...) On the outer wall surface of the engine block based on the flow velocity and turbulence component of the cooling fluid in the vicinity of the outer wall surface, and the finite element. A temperature distribution calculation unit 22 for obtaining a temperature distribution of the engine block using heat flux distributions qn (q1, q2,...) At a plurality of positions on the inner wall surface of the engine block divided into two, and the engine block inner wall from the obtained temperature distribution. The deviation between the heat flux calculation unit 23 for obtaining the heat flux distribution of the engine block and the obtained heat flux of the engine block inner wall and the heat flux of the inner wall of the engine block is obtained, and whether the deviation is within a predetermined range. A deviation calculating / determining unit 24 for determining whether or not and a heat flux updating unit 25 for updating the heat flux distribution qn when the deviation is determined to be outside a predetermined range are functionally provided.

  Next, the thermal analysis method according to the present invention will be described with reference to the flowcharts of FIGS. When the program is started, the 3D model first input from the input device 1 or the 3D model read from the file system 4 is divided into meshes or finite elements for FEM analysis by the shape calculation unit 20. Is done. If the shape data read from the file system 4 has already been divided into finite elements, the division process is omitted.

  When the finite element division ends, in step S1 of FIG. 2, the shape data of the engine block divided into finite elements is input, and the vehicle speed, atmospheric pressure, and fluid viscosity coefficient are input as initial conditions. Further, initial values are set for the outside air temperature, the temperature distribution on the outer wall surface of the engine block, and the heat flux distribution on the inner wall surface, which are referred to in step S4 described later. In step S2, fluid behavior analysis in the vicinity of the outer wall surface of the engine block is performed on the mesh or the finite element division model using the basic equations of the momentum conservation equation, the pressure equation, and the turbulent flow model equation. Velocities and turbulence components are required. This analysis is performed by the fluid behavior analysis function 32a of the heat transfer coefficient calculator 32, and the analysis result is output to the heat transfer coefficient calculation function 32b.

  FIG. 3 is a flowchart showing a procedure for analyzing the behavior of the fluid. In step S101, momentum conservation equations for each of the x, y, and z axes are calculated using the flow velocity distribution, the pressure distribution, and the assumed viscosity coefficient as parameters. And the assumed flow velocity distribution is updated. In step S102, the pressure equation derived from the mass equation is applied to the updated flow velocity distribution to correct the assumed pressure distribution. In step S103, the viscosity coefficient in consideration of turbulent flow is calculated by the turbulent flow model equation using the updated flow velocity distribution. In the present embodiment, the flow velocity and the turbulent component of the cooling fluid in the vicinity of the wall surface are obtained using a model combining a low Reynolds number type k-ε turbulent model and a wall function in consideration of the outer wall boundary condition.

  In the prior art, the energy conservation equation is calculated following the calculation of the turbulent flow model equation in step S103, and the amount of heat flowing into and out of the heat transfer boundary surface is obtained. In this embodiment, the outer wall of the engine block is Since the heat transfer coefficient distribution αn is fixedly obtained for a specific vehicle speed, this procedure is omitted. Therefore, the behavior calculation of the cooling fluid is simplified in this embodiment. In step S104, convergence determination is performed, and the above-described processes are repeated until all calculation results of the fluid flow velocity distribution, pressure distribution, and viscosity coefficient satisfy predetermined convergence conditions.

  Returning to FIG. 2, in step S3, the heat transfer coefficient distribution αn of the engine block outer wall is obtained as the thermal boundary condition based on the flow velocity distribution of the fluid obtained in step S2 and its turbulent flow component. In the present embodiment, as shown in the following equation (1), the heat transfer coefficient α1 is calculated based on T. von Karman's analogy for obtaining the heat transfer coefficient in the forced convection field. This heat transfer coefficient is performed by the heat transfer coefficient calculation function 32b of the heat transfer coefficient calculator 32.

  Here, “ρ” is the density of the cooling fluid, “Us” is the flow velocity of the cooling fluid near the wall surface, “τw” is the shear stress, “Pr” is the Prandtl number, and the shear stress “τw” is the engine It is obtained from the turbulent flow component near the block wall surface.

  In subsequent step S4, the heat conduction analysis unit 33 performs heat conduction analysis. In step S4, the heat flux distribution qo of the outer wall is obtained from the heat transfer coefficient distribution αn obtained in step S3 using the following equation (2). Furthermore, by using the heat flux distribution qo of the outer wall and the heat flux distribution of the inner wall obtained here, the inner and outer walls and the temperature of the engine block calculate the energy conservation equation until the calculation result converges. It is calculated by repeating.

(Equation 2)
qo = α (T−Tx) (2)

  Here, “T” is the outer wall temperature, and “Tx” is the outside air temperature. In step S5, based on the heat conduction calculation result obtained in step S4, the heat flux updating unit 25 updates the outer wall temperature and the inner wall heat flux distribution, which are the inner and outer wall boundary conditions of the engine block. In step S6, combustion gas flow and combustion calculation are performed using the inner wall temperature obtained in step S4.

  FIG. 4 is a flowchart showing the combustion gas flow and the combustion calculation procedure. In step S201, a momentum conservation equation is calculated. In step S202, a pressure equation derived from the mass equation is calculated. In step S203, a turbulent model equation is calculated. In step S204, a spray particle transport model equation is calculated. In step S205, the chemical reaction and the calorific value are calculated. In step S206, an energy conservation equation is calculated. In step S207, calculation of a gas state equation and gas transport (diffusion equation) is performed. In step S208, a convergence determination is made, and the process returns to step S201 until each calculation result converges, and the above-described processes are repeated.

  Returning to FIG. 2, in step S7, the boundary condition of the inner wall of the engine block is updated. That is, the value of the heat flux distribution on the inner wall surface of the engine block obtained in the calculation of the energy conservation formula (step S206) is used as the boundary condition for the heat conduction calculation in the next engine block (step S4). . In step S8, a convergence determination is made. The heat flux distribution of the inner wall obtained in step S6 and the outer wall temperature updated in step S5 and the heat flux distribution and outer wall of the inner wall used in the calculation in step S4. The difference with temperature is compared. If it is determined that the deviation between the two exceeds the reference value and has not yet converged, the process returns to step S4 and the above-described processes are repeated. If it is determined in step S8 that the deviation between the two is below the reference value and has already converged, the process proceeds to step S9. In step S9, the analysis result is output.

  In step S10, the crank angle is updated by a predetermined angle. That is, in this embodiment, the combustion chamber shape continuously changes depending on the position of the piston that moves up and down with the rotation of the crankshaft in the engine block, so in step S10, the crank angle is updated by a predetermined angle, and thereafter Returning to step S4, the above-described processes are repeated.

  In step S1, several vehicle speeds are set as initial conditions, and the behavior calculation of the cooling fluid in step S2 is executed with respect to the several vehicle speeds. In step S3, the vehicle speeds correspond to the several vehicle speeds. A heat transfer coefficient to be calculated, and based on this, heat transfer coefficients at vehicle speeds other than a few are obtained by interpolation, and the calculation after step S4 is performed using the heat transfer coefficient determined for each vehicle speed, If the combustion analysis in the engine block is performed, it is not necessary to calculate the heat transfer coefficient corresponding to the continuous change in the vehicle speed, so that the number of cooling fluid behavior calculations can be reduced.

It is a block diagram of the thermal analysis apparatus which concerns on this invention. It is the flowchart which showed the procedure of the thermal analysis method which concerns on this invention. It is the flowchart which showed the behavior calculation procedure of the cooling fluid. It is the flowchart which showed the cylinder gas flow and combustion calculation procedure. It is the flowchart which showed an example of the conventional thermal analysis procedure. It is the flowchart which showed another example of the conventional thermal analysis procedure. It is a functional block diagram of a thermal analysis apparatus. It is the block diagram which showed the structure of the principal part of the engine made into analysis object.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Input device, 2 ... Analysis part, 3 ... Display part, 20 ... Shape calculation part, 21 ... Heat transfer coefficient calculation part, 22 ... Temperature distribution calculation part, 23 ... Specific point temperature calculation part, 24 ... Deviation calculation and discrimination | determination Part, 25 ... heat transfer coefficient update part

Claims (5)

In a thermal analysis method for performing a thermal analysis inside the object by performing a target area division to divide the object into a finite number of elements and applying a wall boundary condition of the heat conduction calculation of the object to the target area division result,
A first procedure for calculating the behavior of the cooling fluid flowing around the object and determining its flow velocity and turbulence component;
A second procedure for calculating a heat transfer coefficient at a heat transfer boundary between the outer wall of the object and the cooling fluid based on a flow velocity and a turbulent flow component of the cooling fluid;
And a third procedure for performing a thermal analysis inside the object using the calculated heat transfer coefficient. The object is an engine block in which a combustion chamber is formed;
A fourth procedure for updating the thermal boundary condition of the inner and outer walls of the engine block;
A fifth procedure for performing combustion gas flow and combustion calculation;
A sixth procedure for updating a boundary condition of the inner wall of the engine block based on the calculation result;
The thermal analysis method according to claim 1, further comprising a seventh procedure in which the fourth to sixth steps are repeated until the boundary condition converges.   The thermal analysis method according to claim 2, wherein the behavior calculation of the cooling fluid includes a momentum conservation formula calculation, a pressure equation calculation, and a turbulent flow model calculation, and does not include an energy conservation formula calculation. In the first procedure, the behavior calculation of the cooling fluid is performed with respect to an arbitrary plurality of vehicle speeds;
In the second procedure, the heat transfer coefficient at the heat transfer boundary between the outer wall of the object and the cooling fluid is calculated for each of the plurality of vehicle speeds, and further, based on the heat transfer coefficient calculated for each vehicle speed, The thermal analysis method according to claim 1, wherein the heat transfer coefficient at a vehicle speed other than a plurality of points is interpolated.   A thermal analysis program for causing a computer to execute the thermal analysis method according to claim 1.

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