JP2012177625A - Device and method for predicting diffusion of compressible fluid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To predict a predicted diffusion state of hydrogen when hydrogen blows out from a blowout part of a hydrogen supply pipe of a fuel battery electric vehicle in short time.SOLUTION: A compressible fluid diffusion prediction device, which divides a hydrogen blowout part into first to third stages of calculation areas R1-R3 in order from the nearest part of a hydrogen supply pipe 33, performs calculation of a diffusion state of compressible fluid in R1 by a compression, stationary calculation system by a k-ω SST model, performs calculation of a diffusion state of the compressible fluid in R2 by an incompressible, stationary calculation system by the k-ω SST model, and performs calculation of a diffusion state of the compressible fluid in R3 by an incompressible, geostationary calculation system by an RSM model.

Description

  The present invention relates to a compressible fluid diffusion prediction apparatus and method for predicting a diffusion progress state of a compressive fluid at an ejection portion when the compressive fluid is ejected at a high pressure to the ejection portion.

  A fuel cell electric vehicle is equipped with a hydrogen tank that stores hydrogen as a fuel, and supplies the hydrogen in the hydrogen tank to the fuel cell via a pipe to generate power in the fuel cell.

  Hydrogen has characteristics that are not found in other fuels, such as colorlessness, odorlessness, the smallest specific gravity, and quick diffusion, and is designed with consideration for these characteristics (eg, hydrogen sensor mounting position and diffusion space shape). It is important to carry out fuel cell electric vehicles.

  Conventionally, the hydrogen diffusion state has been measured by a hydrogen sensor (a hydrogen sensor used in the measurement test is not a hydrogen sensor that detects the presence of hydrogen but a hydrogen sensor that detects the hydrogen concentration) through a measurement test using a vehicle. Since a study was made on the shape of the diffusion space, the mounting position of the hydrogen sensor, etc., it took a long time to determine these layouts. On the other hand, if the behavior of hydrogen flowing while diffusing in the diffusion space can be analyzed in a short time by compressible fluid diffusion prediction, the shape of the diffusion space can be examined from the design stage.

  However, until now there have been reports of accuracy verification by performing hydrogen diffusion compressible fluid diffusion prediction for simple shapes (for example, Non-Patent Documents 1 and 2), but compression for complex shapes of fuel cell electric vehicles. As a result of investigating research reports in the field of hydrogen application technology, there are no examples that verify the accuracy of the prediction of ionic fluid diffusion and prove that it is a method that can be applied to design studies.

  Patent Document 1 is not a prediction by simulation, but when a gas leak actually occurs in a petrochemical industry plant, the leak location and weather conditions are detected, and based on these, the diffusion direction and diffusion range of the leaked gas are determined. A method for predicting from a calculation formula is disclosed. According to the prediction method, the gas diffusion angle α and the average wind angle β of the wind direction are calculated based on the wind direction wind speed data at the time of gas leakage detection, the reference line is extended from the gas detection point to the leeward side of the average wind direction, A fan-shaped region in which the region of the central angle range of α + β with the reference line as the center line and the circle having the radius of the gas arrival distance up to each time point around the leak location is estimated as the gas diffusion region at each time point (patent) 3 and 4 of Literature 1).

  Non-Patent Document 3 discloses two methods for simulation of hydrogen diffusion: a virtual smoke source method and a diffusion space division method. In the simulation of the virtual smoke source method, the vicinity of the jet part that requires compression calculation is not calculated, but the boundary condition is set using the theoretical formula for the jet flow from the circular jet outlet, and the remaining area is calculated.

  In the simulation of the diffusion space division method, a region having a Mach number greater than 0.5 in the vicinity of the ejection site is divided and calculated as a compressive region, and the remaining incompressible region is calculated using the result as a boundary condition. Since the compression calculation is limited to only the necessary area, the calculation time can be shortened. Further, unlike the virtual smoke source method, the diffusion space division method can be calculated by reproducing a complicated space shape.

Japanese Patent No. 30255503

Michel R.S., Eric S.G, Mathieu N.S: Risks of leaking hydrogen from containers and pipelines, US DOE Hydrogen Program Review Bulletin, NREL / CP-570-25315 (1998) [Michael, RS , Eric, SG, Matthew, NS: Risk incurred by hydrogen escaping from containers and conduits, Proceedings of 1998 US DOE Hydrogen Program Review, NREL / CP-570-25315 (1998)] Chobereb AV, Devar J, Chen Z, Kofu R, Rosec R, Lee C: Hydrogen CF modeling, SAE J2578 test method diffusion experiment, 2nd International Conference on Hydrogen Safety (hydrogen tank 2007) [Tchouvelev, AV, Devaal, J., Cheng, Z., Corfu, R., Rozek, R., Lee, C .: CFD modeling of hydrogen., Dispersion experiments for SAE J2578 test methods development, 2nd International Conference of Hydrogen Safety (2007)] New Energy Industrial Technology Development Organization: Effective Use Guidebook for Hydrogen

  For example, in a fuel cell electric vehicle, a hydrogen supply pipe, a valve, and the like are accommodated in a space partitioned from the passenger compartment by a complex surface-shaped wall material at the rear and lower portions of the passenger compartment. Other parts are also arranged in the accommodation space, and the diffusion space in the case of hydrogen leakage has a complicated shape. In addition, the shape of the diffusion space includes the outer surface shape of the diffusion space and the inner surface shape determined from the surface shape of the components accommodated in the diffusion space.

  The leakage gas diffusion prediction of Patent Document 1 is a gas diffusion prediction after gas leakage actually occurs, and predicts horizontal gas diffusion in an outdoor space where there are no obstacles around. Similar to the diffusion prediction by the simulations of Patent Documents 1 and 2, it is difficult to predict the leakage gas diffusion into the diffusion space having a complicated shape.

  In the simulation calculation by the smoke source method of Non-Patent Document 3, the calculation time is shortened, but the circular range in the vicinity of the ejection part requiring compression calculation is omitted, and there is an obstacle in the vicinity of the ejection part. Is difficult to apply and is not suitable for analysis of complex shapes.

  Although the simulation of the diffusion space division method of Non-Patent Document 3 can be applied to the prediction of the hydrogen diffusion state at the complex-shaped ejection site, the present inventor uses the diffusion space division method of Non-Patent Document 3. As a result, it was found that the current computer performance required about 3 weeks to calculate for one second even if parallel calculation was performed. Moreover, since it is desired to analyze the hydrogen diffusion behavior on the order of several seconds to several tens of seconds, the examination period cannot be shortened as compared with the examination based on the conventional measurement.

  An object of the present invention is to provide a compressible fluid diffusion prediction apparatus and method capable of predicting the diffusion state of a jet compressible fluid in a diffusion space having a complicated shape by greatly reducing the calculation time.

The compressive fluid diffusion prediction apparatus according to the first aspect of the present invention presets the shape of the diffusion space and the ejection portion of the compressive fluid in the diffusion space for the compressive fluid, and the compressive fluid is ejected from the ejection portion. A compressive fluid diffusion prediction apparatus for predicting the progress of diffusion of the compressive fluid in the diffusion space when the diffusion is performed with the side closer to the ejection site in the diffusion space being the inner side and the far side being the outer side. In the calculation of the diffusion state of the compressible fluid in each calculation area, the dividing means for dividing the space into three or more calculation areas from the inside to the outside, the compression / steady calculation method is applied to the innermost calculation area. Allocate and assign the uncompressed / unsteady calculation method to the outermost calculation area, assign the uncompressed / steady calculation method to the intermediate calculation area, and apply it to each calculation area. The turbulence model selection means for selecting a turbulent model, the calculation method assigned by the calculation method assignment means for each calculation area, and the turbulent model selection means for the diffusion state of the compressible fluid in each calculation area Calculated from the turbulent flow model, and based on this calculation, the diffusion of the compressive fluid in each calculation region at each discrete time from the start of the ejection of the compressive fluid, A point-by-time diffusion state calculation means for calculating the diffusion state of the compressible fluid in the space;
Prediction means for predicting the diffusion state of the compressible fluid in the diffusion space for each lapse of discrete time calculated by the time-dependent diffusion state calculation means as the diffusion progress state of the compressive fluid in the diffusion space up to each elapsed time And.

  According to the first aspect of the present invention, the ejection part is divided into three or more diffusion spaces in the direction away from the compressive fluid side, and an intermediate calculation area is inserted between the innermost calculation area and the outermost calculation area. In addition, it is possible to reduce the calculation time of the entire diffusion space by generating a diffusion space portion that can be completed by non-compression and steady calculation while guaranteeing a predetermined prediction accuracy.

  In the compressible fluid diffusion prediction apparatus according to a second aspect of the invention, the dividing unit divides the diffusion space into a plurality of meshes as regions smaller than the calculation region, and a boundary between the plurality of calculation regions is a boundary between meshes. The diffusion space is divided into the plurality of calculation regions so that the time-dependent diffusion state calculation means calculates the concentration of the compressible fluid in units of meshes, and the concentration of the compressive fluid in the diffusion space is calculated. The distribution is calculated as a diffusion state of the compressive fluid in the diffusion space, and the dividing unit determines the division state of the diffusion space by a mesh and the Mach number of the compressive fluid in each part of the diffusion space and the diffusion space. And the number of intermediate calculation areas and boundaries are calculated when the concentration of all meshes is calculated for each lapse of discrete time by the time-dependent diffusion state calculation means. There as a minimum, and sets.

  As a result of calculating the diffusion state of the compressive fluid in the diffusion space as the concentration of the compressive fluid in units of meshes, the division state of the diffusion space by the mesh affects the calculation time of the diffusion state of the compressive fluid. For this reason, the number of intermediate calculation regions whose boundaries are determined by the division state of the diffusion space by the mesh and the setting of the boundaries also affect the calculation time of the diffusion state of the compressible fluid. According to the second invention, since the number and boundaries of the intermediate calculation regions can be appropriately set, it is possible to shorten the simulation calculation time for the entire diffusion space.

  The compressible fluid diffusion prediction device according to a third aspect of the present invention is the compressive fluid diffusion prediction device according to the first and second aspects, wherein the diffusion space is a space defined by at least an upper side and a side wall, The turbulence model selection means selects the turbulence model that can calculate the anisotropy of the turbulence for the outermost calculation area, and the calculation accuracy for the jet turbulence for the innermost calculation area. It is characterized by selecting a turbulent model to be secured.

  In the fuel cell electric vehicle, the hydrogen tank and the pipe are generally arranged in a housing space having a complicated shape, which is partitioned upward and laterally by a partition member.

  According to the third invention, a turbulent flow model capable of calculating the anisotropy of turbulent flow is selected in the outermost calculation region, and the turbulence that ensures calculation accuracy for the jet turbulent flow is calculated for the innermost calculation region. By selecting the flow model, it is possible to improve the prediction accuracy of the diffusion state of the compressive fluid when the compressive fluid is ejected from a fuel cell electric vehicle or the like.

  A compressible fluid diffusion prediction apparatus according to a fourth aspect of the present invention is the compressive fluid diffusion prediction apparatus according to the third aspect of the present invention, further comprising display means for displaying the predicted diffusion progress state predicted by the prediction means.

  According to the fourth aspect of the invention, the analyst can look at the display and examine the shape of the diffusion space, the layout of components in the diffusion space, and the like.

  The compressible fluid diffusion prediction apparatus according to a fifth aspect of the present invention is the compressive fluid diffusion prediction apparatus according to the fourth aspect of the invention, wherein the display means predicts each of a plurality of diffusion conditions including the shape of the diffusion space. A plurality of predicted diffusion progress states are displayed in a comparable manner.

  The analyst can see the prediction result of the diffusion progress state of the compressible fluid in the diffusion space predicted for each diffusion condition, and can appropriately design the diffusion space based on the prediction result.

  In the compressive fluid diffusion prediction method of the sixth aspect of the present invention, the shape of the diffusion space and the jetting site of the compressive fluid in the diffusion space are preset for the compressive fluid, and the compressive fluid is jetted from the jetting site. A compressive fluid diffusion prediction method for predicting the progress of diffusion of the compressive fluid in the diffusion space at the time, wherein the computer sets the side closer to the ejection site in the diffusion space to the inner side and the far side to the outer side. Dividing the diffusion space into three or more calculation regions from the inside to the outside, and the computer calculates the compression state in the innermost calculation region in the calculation of the diffusion state of the compressible fluid in each calculation region. Assign a steady calculation method, assign an uncompressed / unsteady calculation method to the outermost calculation region, and assign an uncompressed / steady calculation method to the intermediate calculation region. A turbulence model selection step in which the computer selects a turbulence model to be applied to each calculation area; and the computer calculates the diffusion state of the compressible fluid in each calculation area with respect to each calculation area. Calculated according to the calculation method assigned in the assigning step and the turbulent flow model selected in the turbulent model selection step, and each calculation region at the time when each discrete time has elapsed from the start point of ejection of the compressible fluid based on this calculation A step-by-time diffusion state calculation step for calculating the diffusion state of the compressive fluid in the diffusion space at this time point from the diffusion state of the compressive fluid at The diffusion state of the compressive fluid in the diffusion space over time, the diffusion space up to each time point Characterized in that it and a prediction step of predicting the progress of diffusion of the definitive compressive fluid.

  According to the sixth aspect of the invention, by dividing the ejection part into three or more diffusion spaces on the side away from the compressive fluid side and inserting an intermediate calculation area between the innermost calculation area and the outermost calculation area In addition, it is possible to secure a diffusion space portion that can be processed by non-compression and steady calculation while guaranteeing a predetermined prediction accuracy, and to shorten the calculation time of the entire diffusion space.

The schematic block diagram of the fuel cell electric vehicle carrying a hydrogen tank. Explanatory drawing about the spreading | diffusion of hydrogen in the lower side space of a floor panel when the ejection of hydrogen arises from the predetermined site | part of a hydrogen supply pipe | tube. Explanatory drawing of the diffusion space in the three-stage division calculation method. The graph which shows the comparison of each calculated value and experimental value when carrying out the simulation calculation of the hydrogen concentration on the ejection axis | shaft to the calculation area | region of the 1st step | paragraph by making a jet nozzle diameter and the jet flow volume the same with various turbulence models. Calculations and experiments when calculating the hydrogen concentration on the jet axis up to the first stage calculation area for the three combinations of jet diameter and jet flow, and selecting the turbulent model as the k-ω SST model A graph that compares values. The graph which shows the comparison of each calculated value and an experimental value when carrying out the simulation calculation of the hydrogen concentration on the ejection axis | shaft in the calculation area | region of a 3rd step | paragraph by making a jet nozzle diameter and the ejection flow volume the same with various turbulent models. The figure which shows the hydrogen ejection site | part selected in the fuel cell electric vehicle used in order to verify the contrast relationship of calculation time and calculation accuracy. Explanatory drawing of the attachment position of the three hydrogen sensors selected in the motor vehicle used for verification. The contour figure of the hydrogen concentration about the calculation result of each stage in the three-stage division | segmentation calculation by the simulation for collating with the experimental result of the verification experiment in the motor vehicle used for verification. The graph which shows the result compared with the measured value in the evaluation point of hydrogen concentration. The hardware block diagram which implement | achieves a compressible fluid diffusion prediction apparatus. The block diagram of a compressible fluid diffusion prediction apparatus. The flowchart of the prediction method which a compressible fluid diffusion prediction apparatus implements.

[Hydrogen ejection in fuel cell electric vehicles]
In FIG. 1, a fuel cell electric vehicle 10 is equipped with a front wheel 12 and a rear wheel 13 below a front portion and a rear portion of a vehicle body 11. The vehicle compartment 16 is formed in the vehicle body 11, and the lower side is defined by a floor panel 17.

  The floor panel 17 is raised at the rear end portion to define the lower end portion of the rear wall of the vehicle body 11. The hydrogen tank 20 is disposed on the inner surface side of the raised portion of the floor panel 17. The fuel cell 21 is disposed below the middle portion of the floor panel 17 in the front-rear direction, and generates power using hydrogen from the hydrogen tank 20. Both the motor 22 and the battery 23 are disposed in a space in the hood of the vehicle body 11. The generated power of the fuel cell 21 is stored in the battery 23, and the motor 22 is operated by the power from the battery 23 to drive the front wheels 12 of the drive wheels.

  The hydrogen sensor 28 is disposed above the housing space portion of the hydrogen tank 20 and detects the hydrogen concentration in the housing space portion of the hydrogen tank 20. The hydrogen sensor 29 is disposed above the housing space portion of the fuel cell 21 and detects the hydrogen concentration in the housing space portion of the fuel cell 21. The hydrogen sensor 30 is disposed on the ceiling of the passenger compartment 16 and detects the hydrogen concentration in the passenger compartment 16. The hydrogen sensors 28 to 30 detect the hydrogen concentration at each mounting location, but the number and mounting locations of the hydrogen sensors deployed in the fuel cell electric vehicle 10 are appropriately selected, and the fuel cell electric vehicle 10 is out of the path. When a hydrogen eruption occurs, it must be able to detect it quickly.

  In FIG. 2, the hydrogen tank 20 is arranged on the lower side of the floor panel 17 with the axis line aligned in the horizontal direction of the fuel cell electric vehicle 10. In the vicinity of the hydrogen tank 20, the hydrogen supply pipe 33 projects horizontally from the hydrogen tank 20 along the axis of the hydrogen tank 20, and guides compressed hydrogen to the fuel cell 21. In FIG. 2, it is assumed that hydrogen leaks at a predetermined location of the hydrogen supply pipe 33, and compressed hydrogen is ejected upward from the ejection portion 34, as in F1.

  The space below the floor panel 17 is assumed to be a complex space, and the tank peripheral parts 36 to 38 are arranged in the vertical range between the horizontal upper wall portion of the floor panel 17 and the hydrogen tank 20 and also to the side of the tank. It is assumed that the component 40 exists on the lateral side of the hydrogen tank 20 in the horizontal direction.

  In FIG. 2, (a) is an enlarged view of Rx in (b). In FIG. 2A, the compressed hydrogen is ejected upward from the ejection part 34 of the hydrogen supply pipe 33 and linearly advances upward in the range of Rx. In the jet immediately after jetting, it is only hydrogen, and as it goes upward, the surrounding air is entrained and mixed with air. In Rx, air vortices are generated in a plurality of layers in the vertical direction in a range outside the straight-forward portion of hydrogen spreading outwardly.

  In FIG. 2B, when the hydrogen coming out from the upper boundary of Rx hits the slope of the floor panel 17, the direction changes and rises along the slope of the floor panel 17 as indicated by F2. Next, the hydrogen flows along the horizontal portion on the upper surface of the floor panel 17 toward the end portion of the hydrogen tank 20 on the side opposite to the hydrogen supply pipe 33. The hydrogen pressure gradually decreases to atmospheric pressure.

  Hydrogen generates a vortex as shown by F3 in the vicinity of the end on the opposite side of the horizontal upper wall portion of the floor panel 17 from the hydrogen supply pipe 33. Then, it descends along the slope of the floor panel 17. The hydrogen sufficiently approaches 1 atm in the vicinity of the end of the hydrogen tank 20 on the side opposite to the hydrogen supply pipe 33, and thereafter rises by buoyancy as indicated by F4.

  The three-stage division calculation method described below was devised as a method for predicting the progress of the diffusion state in a short time based on the hydrogen ejection state in the fuel cell electric vehicle 10 described above. It was verified that the prediction accuracy was obtained.

[Three-stage division calculation method]
In FIG. 3, R1 to R3 correspond to the first to third calculation areas and are a three-dimensional space. H represents ejected hydrogen. As will be described later, the diffusion space for calculating the hydrogen diffusion state is divided into three calculation regions R1 to R3. If the side closer to the ejection part 34 is defined as the inner side and the side far from the ejection part 34 is defined as the outer side, R2 is adjacent to the outer side of R1, and R3 is adjacent to the outer side of R2.

The boundary surface between the calculation areas R1 to R3 will be described based on the calculation formula (1) for the Courant number C.
C = (v · Δt) / Δx (1)
However, the meaning of each symbol is as follows.
v: fluid velocity Δt: time step
Δx: Mesh size

  The compression represents the number of moving meshes of fluid per time step, and if it is too large, the numerical value diverges during iterative calculation and the accuracy decreases due to the loss of the high-frequency component of the time change. Even if an implicit method capable of non-stationary calculation with one or more compressions is used, the upper limit of the Courant number C is about 40 in order to perform a reliable calculation.

  In the unsteady calculation including the vicinity of the jet outlet where the flow velocity v is high and the mesh size Δx is small, the time step Δt must be reduced in order to satisfy the constraint of the Courant number C <40. This increases the calculation time by increasing the number of time steps until the calculation of the diffusion state of the compressive fluid when a predetermined time has elapsed since the start of the ejection of the compressive fluid.

  The boundary surface between R1 and R2 is defined as a boundary surface that divides a compressive diffusion space inside the boundary surface and an incompressible diffusion space outside the boundary surface. For example, the boundary surface has a Mach number of 0.5. A surface. That is, in this example, R1 is a calculation region where Mach number ≧ 0.5, and R2 and R3 are calculation regions where Mach number <0.5. Since the sound velocity of hydrogen is 1200 m / s, the Mach number = 0.5 is v = 600 m / s in the equation (1).

  Note that Δt and Δx are defined so that the Mach number ≧ 0.5 in hydrogen is in a region where the Courant number C is sufficiently smaller than 40. Δt is defined as a common value in R1 to R3. Δx may be set to one value over the entire diffusion space, or standard for each diffusion space R1 to R3 so that the calculation accuracy of the hydrogen diffusion state in each calculation region of R1 to R3 is within an allowable value. You can also set a value. In each calculation area, a common value can be set smaller than other places in the vicinity of the part (part) without setting a common value. Since the flow velocity decreases in the outer calculation area, the standard (default) mesh size of each calculation area that keeps the calculation accuracy of each calculation area within the allowable value is increased in the outer calculation area to shorten the calculation time. be able to. However, Δx needs to be a mesh size of 5 mm or less at R3 in order to reproduce the complex shape for a complex-shaped ejection portion such as the housing space of the hydrogen tank 20 of the fuel cell electric vehicle 10. is there.

  The boundary surface between R2 and R3 is set so that the Courant number C> 40 at the inner R2 and the Courant number C ≦ 40 at the outer R3.

  In the calculation of the diffusion state of the compressive fluid at the ejection site, the mesh is first set in the diffusion space, the Mach number and the Couran number of each mesh are calculated, the boundary surface between R1 and R2, and R2 and R3 Then, the process proceeds to calculation of the diffusion state of the compressible fluid in each mesh for each calculation region. The calculation of the diffusion state of the compressible fluid is performed in order from the inner calculation area, and when the calculation of the diffusion state of the compressible fluid in each calculation area is completed, the boundary value at the boundary with the diffusion space adjacent to the outer side is calculated. After that, the calculation of the diffusion state of the compressive fluid in the mesh of the diffusion space adjacent to the outside starts with the calculation method in the diffusion space. In the same diffusion space, the diffusion state of the compressible fluid in each mesh is calculated in order from the inner mesh to the outer mesh (or in the hydrogen traveling direction).

  R1 is a compression calculation area, and R2 and R3 are non-compression calculation areas. R1 and R2 are assumed to be steady calculation areas, and R3 is assumed to be a non-steady calculation area. In other words, the calculation of the diffusion state of the compressible fluid in R1 is performed by the compression / steady calculation method, the calculation of the diffusion state of the compressible fluid in R2 is performed by the non-compression / steady calculation method, and the compression fluid in R3 is calculated. The calculation of the diffusion state is performed by an uncompressed / unsteady calculation method. For example, an implicit method or a SIMPLE method is used for the calculation. In order to consider the buoyancy of hydrogen as a compressible fluid, for example, a model in which a gravity equation is added to the volume term of the Naviestokes equation is used. In order to calculate the mixing and diffusion of hydrogen and air, for example, a model that considers turbulent diffusion based on the diffusion formula of FICK is used.

  In addition, if the calculation of the diffusion state of the compressive fluid in R1 and R2 to which the steady calculation method is assigned is performed once, it is preferable to continue using the calculation results as long as the flow of the compressive fluid does not change greatly. For example, when the diffusion state of the compressive fluid in the diffusion space is predicted by simulation from the start of ejection to the lapse of Te, the ejection of the compressive fluid maintains the ejection flow rate Q1 from the start to Ts (Ts <Te). Assuming that the ejection flow rate becomes 0 after the lapse of time (the ejection end), the same diffusion state of the compressive fluid in R1 and R2 in the simulation from the ejection start to the Te lapse continues to be used.

  On the other hand, the calculation of the diffusion state of the compressible fluid in R3 to which the unsteady calculation method is assigned is performed every time step Δt has elapsed. When calculating the diffusion state of the compressible fluid in the entire diffusion space at each time step after the time step Δt has elapsed from the start of the ejection of the compressive fluid, the diffusion of the compressive fluid at R1 to R3 at each time step has elapsed. The states are connected at the boundaries of R1 to R3, and the diffusion state of the compressible fluid in the entire diffusion space is calculated.

  The effect of turbulent diffusion mixed with turbulent flow or turbulent mixing is more dominant in the diffusion phenomenon in a flow field than in molecular diffusion caused by concentration differences. Turbulent flow calculation methods include direct numerical compressible fluid diffusion prediction (DNS), large / eddy / compressible fluid diffusion prediction (LES), and Reynolds average model (RANS). Since DNS and LES for exact calculation of all or part of the vortex have too high calculation load, it is appropriate to select RANS in practice.

  Many RANS turbulence models have been developed, but there is no universal model for any calculation object. In order to achieve the target accuracy of compressive fluid diffusion prediction, it is necessary to select a model that can be calculated accurately for each region of the division calculation.

We selected five turbulence models that have been applied to engineering calculations as candidates, and selected turbulence models for jet turbulence generated in the jet and wall turbulence generated by wall flow. The following five turbulent models (a) to (e) are used as candidates.
(A) k-ω standard, (b) k-ω SST, (c) k-ε standard, (d) k-ε realizable, (e) RSM.

  FIG. 4 shows the hydrogen concentration on the ejection axis up to the first calculation region with the ejection diameter of φ1.4 mm, the ejection flow rate of 120 NL / min, and the ejection direction vertically upward. The comparison between each calculated value and the experimental value when the simulation calculation is performed with each turbulent flow model of () is shown. The horizontal axis represents the distance (m) from the ejection port on the ejection axis, and the vertical axis represents the hydrogen concentration (molar fraction). The k-ω SST model was found to be the most accurate of the five turbulence models.

  The inventor further examined whether or not the predetermined accuracy can be maintained even when the ejection conditions (the diameter of the ejection port and the ejection flow rate) change when the k-ω SST model is adopted as the turbulent flow model. The result is shown in FIG.

In FIG. 5, the meaning of each symbol is as follows.
G1, g1: Experimental value (point) and calculated value (line) when the outlet diameter = φ7 mm and the ejection flow rate = 212 NL / min.
G2, g2: Experimental values (points) and calculated values (lines) when the jet outlet diameter = φ0.5 mm and the jet flow rate = 130 NL / min.
G3, g3: Experimental value (point) and calculated value (line) when the outlet diameter is φ0.1 mm and the jet flow rate is 5.1 NL / min.

  The inventor has confirmed from FIG. 5 that when the k-ω SST model is adopted as the turbulent flow model, the predetermined accuracy can be maintained even if the ejection conditions (the diameter of the ejection port and the ejection flow rate) change.

  Next, the inventor verified the case where the jet nozzle diameter was 7 mm, the jet flow rate was 212 NL / min, and jetted parallel to the horizontal wall surface. Up to the position of 0.14 m on the ejection axis is calculated as the second stage of the three-stage division calculation method, and the range from 0.14 m to 1 m as the third stage calculation is the above (a) to (e). Each of the five turbulence models was calculated. FIG. 6 is a graph comparing the calculation result with the actually measured value.

  In wall turbulence, the two-equation model has a high calculated hydrogen concentration and cannot fully express diffusion. On the other hand, the RSM model, which is a seven-equation model, agrees well with the actual measurement values. The RSM model can calculate the anisotropy of turbulent vortices, and is considered to be able to express the influence of highly anisotropic vertical vortices generated by the velocity difference near the wall surface. We obtained the knowledge that the RSM model should be adopted in the third stage of the split calculation that mainly calculates the flow along the vehicle floor panel.

[Verification experiment in verification vehicle]
In order to confirm the effect of the above calculation method, the inventor conducted experiments and calculations on the vehicle underfloor space around the hydrogen tank 20 in the verification vehicle of the fuel cell electric vehicle 10 to verify the calculation time and calculation accuracy. did. The ejection conditions in the verification experiment were represented by a diameter of 7 mm and a flow rate of 212 NL / min. A jet outlet was installed in the vicinity of the pipe joint next to the hydrogen tank, and hydrogen was jetted vertically upward. The ejection time was 4 seconds.

  FIG. 7 shows an ejection part 34 set as a hydrogen leakage part in the verification vehicle, and the ejection part 34 is set at a position near the hydrogen tank 20 in the hydrogen supply pipe 33 that guides the compressed hydrogen in the hydrogen tank 20 to the fuel cell 21. The hydrogen tank 20 is placed on the platform 50, and the upper part is covered with a raised portion at the rear end of the floor panel 17 and is partitioned from the vehicle compartment 16.

  FIG. 8 shows attachment positions P1 to P3 of the three hydrogen sensors 1 to 3 (FIG. 10) attached to detect the hydrogen concentration of each part in the accommodation space portion of the hydrogen tank 20 with respect to the ejection part 34. ing. In FIG. 8, P <b> 1 to P <b> 3 indicate the upper surface side (outer surface side) of the floor panel 17, but the actual mounting position of the hydrogen sensor is that of the floor panel 17 as the storage side of the hydrogen tank 20 and the hydrogen supply pipe 33. It is the lower surface side (inner surface side). P1 is selected as the uppermost part of the storage space portion of the hydrogen tank 20, P2 is selected as the front side wall part of the storage space part, and P3 is selected as the rear side wall part of the storage space part.

  Regarding the solver in the verification experiment, the solver was calculated by the implicit method and the SIMPLE method using Fluent 6.3 as the solver. In order to consider the buoyancy of hydrogen, a model in which the gravity equation is added to the volume term of the Navier-Stokes equation is used, and turbulent diffusion is considered based on the diffusion formula of FICK in order to calculate the mixing and diffusion of hydrogen and air. The Species model was used.

  The maximum analysis mesh size in the verification experiment was 5 mm.

  In the present invention, the shape of the diffusion space corresponds to the shape of the mesh space in which the mesh is set. Therefore, even if the outer surface shape of the diffusion space is the same, the shape of the diffusion space is different depending on the components in the diffusion space and the arrangement thereof.

  The verification result by the verification experiment will be described. FIG. 9 shows a contour diagram of the hydrogen concentration for the calculation result at each stage in the three-stage division calculation. In FIG. 9, (a) to (c) are contour diagrams of the first-stage calculation area R1 to the third-stage calculation area R3, respectively. The actual contour map screen that is output and displayed on the computer display is color-coded for each hydrogen concentration region. The higher the hydrogen concentration region, the closer the color to warm red, and the lower concentration hydrogen region. It is displayed in a color that is close to the cold blue color.

  In the calculation result of the third stage in FIG. 9C, the behavior of hydrogen flow with diffusion could be visualized. The time required for all calculations was 4 days, which was shorter than the conventional examination period.

  FIG. 10 shows the result of comparison with actual measurement values at evaluation points (attachment positions) P1 to P3 (FIG. 8) of the hydrogen concentration. The calculated values and the measured values were in good agreement with each evaluation point.

  The hydrogen diffusion prediction apparatus 60 that implements the above three-stage division calculation method will be described below.

  FIG. 11 is a hardware configuration diagram of the hydrogen diffusion prediction device 60. The hardware for realizing the hydrogen diffusion prediction device 60 is a well-known hardware of a well-known computer. The CPU 61, ROM 62, RAM 63, communication interface communication I / F 64, hard disk 65, display 66, keyboard 67 and pointing device 68 are connected via a bus 69. The software that realizes the function of the hydrogen diffusion prediction device 60 is stored as a program in the hard disk 65, and the hydrogen diffusion state prediction by the hydrogen diffusion prediction device 60 is executed by the CPU 61 calling the program from the hard disk 65 and executing it. To be implemented.

  FIG. 12 is a block diagram of the hydrogen diffusion prediction device 60. The hydrogen diffusion prediction device 60 includes a dividing means 75, a calculation method assigning means 76, a turbulent flow model selecting means 77, a point-by-time diffusion state calculating means 78, and a predicting means 79 as means realized by software. The operation of the hydrogen diffusion prediction device 60 will be described with reference to the flowchart of FIG. Note that the hydrogen diffusion prediction device 60 sets the shape of the diffusion space and the position of the ejection site for predicting the diffusion state prior to each simulation execution.

  The dividing means 75 divides the housing space portion of the hydrogen tank 20 (hereinafter referred to as “hydrogen diffusion space” as appropriate) as the inner space of the raised portion of the floor panel 17 into the calculation regions R1 to R3 (STEP 91). This corresponds to the division step of the present invention).

  In the calculation of the hydrogen diffusion state in the calculation regions R1 to R3, the calculation method assigning means 76 assigns the calculation method described above for each calculation region (STEP 92, corresponding to the calculation method assigning step of the present invention). When it repeats, the compression / steady calculation method is assigned to R1, the non-compression / steady calculation method is assigned to R2, and the non-compression / non-stationary calculation method is assigned to R3.

  The turbulent flow model selecting means 77 selects the turbulent flow model applied to the calculation of the hydrogen diffusion state in the calculation regions R1 to R3 (STEP 93, corresponding to the turbulent flow model selecting step of the present invention). . To repeat, the k-ω SST model is selected for R1 and R2, and the RSM model is selected for R3.

  The point-by-time diffusion state calculation means 78 selects the hydrogen diffusion state in each calculation region R1 to R3 by the calculation method assigned by the calculation method assignment means 76 to the calculation regions R1 to R3 and the turbulent flow model selection means 77. Calculate according to the turbulence model. Then, the hydrogen diffusion state in the hydrogen diffusion space for each elapse of the time step Δt from the hydrogen ejection start time is calculated from the calculation regions R1 to R3 calculated as the hydrogen diffusion state at the time (STEP 94). This corresponds to the calculation of the diffusion state by time of the present invention.)

  The prediction means 79 predicts the hydrogen diffusion progress state in the hydrogen space from the hydrogen diffusion state at each time step Δt calculated by the time-point diffusion state calculation means 78 (STEP 95). This corresponds to the prediction step of the present invention).

  The prediction result by the prediction means 79 is displayed on the display 66 (STEP 96, corresponding to the display step of the present invention). The prediction specifically displayed on the display 66 is, for example, the contour diagram of FIG. 9 or the graph of FIG.

  The prediction result of the hydrogen diffusion state by the prediction means 79 is stored in the hard disk 65 in association with the diffusion conditions (for example, the shape of the diffusion space, the position of the ejection site, the hydrogen ejection pressure, the ejection flow rate, etc.). Can display the prediction result stored in the hard disk 65 on the display 66 as appropriate. The analyst can also compare a plurality of prediction results under a plurality of diffusion conditions by switching to the same screen simultaneously or appropriately. Based on such a comparison, the analyst performs a design for the fuel cell electric vehicle 10 corresponding to the diffusion condition for obtaining an appropriate diffusion state.

  The compressive fluid diffusion prediction apparatus of the present invention is not limited to simulation prediction about the diffusion state at the time of hydrogen ejection of the storage space portion of the hydrogen tank 20 in the fuel cell electric vehicle 10, and the storage space portion in the fuel cell electric vehicle 10. Other simulation parts and other diffusion spaces, various ejection parts in various diffusion spaces other than the fuel cell electric vehicle 10, and a simulation prediction of a diffusion state at the time of the ejection of a compressible fluid other than hydrogen Can be applied.

  In the embodiment of the present invention, the ejection site is divided into three parts, but the number of divisions can be suitably four or more. In the embodiment, the Mach number at the boundary surface between R1 and R2 is set to 0.5, and the Courant number at the boundary surface between R2 and R3 is set to 40. Accordingly, adjustment can be made within a predetermined range.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell electric vehicle, 17 ... Floor panel, 20 ... Hydrogen tank, 28 ... Hydrogen sensor, 33 ... Hydrogen supply pipe, 34 ... Injection part, 60 ... Hydrogen Diffusion prediction device, 75 ... division means, 76 ... calculation method assignment means, 77 ... turbulent flow model selection means, 78 ... time-dependent diffusion state calculation means, 79 ... prediction means.

Claims (6)

The shape of the diffusion space and the ejection portion of the compressive fluid in the diffusion space are set in advance for the compressive fluid, and the compressive fluid in the diffusion space when the compressive fluid is ejected from the ejection portion is set. A compressible fluid diffusion prediction apparatus that predicts the progress of diffusion,
Division means for dividing the diffusion space into three or more calculation regions from the inside to the outside with the side closer to the ejection portion in the diffusion space as the inside and the far side as the outside,
In the calculation of the diffusion state of the compressible fluid in each calculation area, a compression / steady calculation method is assigned to the innermost calculation area, and an uncompressed / unsteady calculation method is assigned to the outermost calculation area. A calculation method assigning means for assigning an uncompressed and steady calculation method,
Based on the calculation, the diffusion state of the compressible fluid in each calculation region is calculated according to the calculation method assigned by the calculation method assigning unit and the turbulent model selected by the turbulent model selection unit for each calculation region. By time point for calculating the diffusion state of the compressible fluid in the diffusion space at the time point from the diffusion state of the compressive fluid in each calculation region at the time point of each discrete time from the start point of ejection of the compressive fluid. Diffusion state calculation means;
Prediction means for predicting the diffusion state of the compressible fluid in the diffusion space for each lapse of discrete time calculated by the time-dependent diffusion state calculation means as the diffusion progress state of the compressive fluid in the diffusion space up to each elapsed time When,
A compressible fluid diffusion prediction apparatus comprising: The compressible fluid diffusion prediction apparatus according to claim 1,
The dividing means divides the diffusion space into a plurality of meshes as regions smaller than the calculation region, and the diffusion space is divided into the plurality of meshes so that boundaries of the plurality of calculation regions become boundaries between meshes. Divided into calculation areas,
The point-by-time diffusion state calculation means calculates the concentration of the compressible fluid in units of meshes, and calculates the concentration distribution of the compressible fluid in the diffusion space as the diffusion state of the compressive fluid in the diffusion space. ,
The dividing means sets the division state of the diffusion space by the mesh based on the Mach number of the compressible fluid in each part of the diffusion space and the boundary surface of the diffusion space, and the number and boundary of the intermediate calculation regions, A compressible fluid diffusion prediction apparatus, wherein the concentration calculation time for all meshes for each lapse of discrete time by the time point diffusion state calculation means is set to be minimum. The compressible fluid diffusion prediction apparatus according to claim 1 or 2,
The diffusion space is a space defined by wall surfaces at least at the upper side and the side,
The turbulence model selection means selects a turbulence model that can calculate the anisotropy of the turbulent flow for the outermost calculation region, and calculates accuracy for the jet turbulence for the innermost calculation region. A compressible fluid diffusion prediction apparatus characterized by selecting a turbulent flow model to ensure The compressible fluid diffusion prediction apparatus according to claim 3,
A compressible fluid diffusion prediction apparatus comprising display means for displaying a predicted diffusion progress state predicted by the prediction means. The compressible fluid diffusion prediction apparatus according to claim 4,
The display means includes
A compressible fluid diffusion prediction apparatus, wherein a plurality of predicted diffusion progress states predicted by the prediction means are displayed for each of a plurality of diffusion conditions including the shape of the diffusion space so as to be comparable. The shape of the diffusion space and the ejection portion of the compressive fluid in the diffusion space are set in advance for the compressive fluid, and the compressive fluid in the diffusion space when the compressive fluid is ejected from the ejection portion is set. A compressible fluid diffusion prediction method for predicting the progress of diffusion,
A division step in which the computer divides the diffusion space into three or more calculation regions from the inside to the outside with the side closer to the ejection site in the diffusion space as the inner side and the far side as the outer side;
In the calculation of the diffusion state of the compressible fluid in each calculation area, the computer assigns a compression / steady calculation method to the innermost calculation area, and assigns an uncompressed / unsteady calculation method to the outermost calculation area, A calculation method assignment step for assigning an uncompressed / steady calculation method to the intermediate calculation region,
A turbulence model selection step in which a computer selects a turbulence model to be applied to each calculation area;
The computer calculates the diffusion state of the compressible fluid in each calculation region according to the calculation method assigned in each calculation region in the calculation method assignment step and the turbulent flow model selected in the turbulent flow model selection step. Based on the calculation, the diffusion state of the compressible fluid in the diffusion space at the elapsed time is calculated from the diffusion state of the compressible fluid in each calculation region at the time when each discrete time has elapsed from the start of the ejection of the compressible fluid. A diffusion state calculation step for each time point,
The computer predicts the diffusion state of the compressible fluid in the diffusion space for each lapse of discrete time calculated in the diffusion state calculation step for each time point as the diffusion progress state of the compressive fluid in the diffusion space up to each time point. A prediction step to
A compressible fluid diffusion prediction method comprising: