CN110688805A - Analysis method for flow numerical value of automobile external flow field - Google Patents
Analysis method for flow numerical value of automobile external flow field Download PDFInfo
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Abstract
The invention discloses an analysis method of a flow numerical value of an automobile external flow field, which comprises the following steps: (1) carrying out model construction by adopting three-dimensional CAD software according to full-size data of a certain real automobile model, wherein the length L of the whole automobile is 4.6m, the width W of the automobile is 20m, the height H of the automobile is 1.4m, the axle base B is 16m, and (2) a calculation area omega is set, and the whole calculation area of an automobile external flow field is set as follows: omega 7L 7W 4H 325mx14.2mx5.7m, plane z 0m is the symmetry plane of the car body, the origin of coordinates is located at the projection of the front end of the car body on the ground, (3) the calculation region omega is subdivided into unstructured meshes, after subdivision, the total number of the unstructured meshes is about 1.2 × 107The degree of freedom is about DOF 1.03 × 107The size of the grid near the vehicle body reaches millimeter level. The method for analyzing the flow numerical value of the automobile external flow field provided by the invention has the advantages that the huge scale of numerical calculation is greatly reduced, the accuracy is improved, and the method has good parallel expansibility under the condition of thousands of core processors.
Description
Technical Field
The invention relates to the technical field of flow values of automobile external flow fields, in particular to an analysis method of flow values of an automobile external flow field.
Background
With increasingly exhausted petroleum resources on the earth and continuous rising of petroleum price, at present, more and more countries pay attention to the aerodynamic performance of automobiles so as to improve the fuel economy of the automobiles, with the rapid development of computer technology, the CFD technology is increasingly applied to automobile design, numerical simulation can be carried out on an automobile outflowing field by means of CFD software, so that the pressure distribution of the surface of an automobile body, the speed and the pressure distribution of the outflowing field, the aerodynamic resistance and the aerodynamic lift value, the wind resistance coefficient, the lift coefficient and the like of the automobile body can be obtained, the aerodynamic performance of the automobile can be visually displayed through a graph, the modeling design of the automobile body can be guided according to the numerical simulation, and the method has important significance for reducing the cost, shortening the research and development period and improving the autonomous development design capability of products.
The existing analysis method for the flow numerical value of the external flow field of the automobile is influenced by factors such as complex appearance, high Reynolds number and the like, and the numerical value of the flow of the external flow field of the automobile is large in calculation scale and difficult to accurately solve. Developing efficient parallel algorithms to numerically solve the outflow problem using supercomputing platform resources has become a research hotspot in this field.
Disclosure of Invention
The invention aims to provide an analysis method for flow values of an automobile external flow field, so as to solve the problems in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme: an analysis method for flow values of an automobile external flow field comprises the following steps:
(1) carrying out model construction by adopting three-dimensional CAD software according to full-size data of a certain real vehicle model, wherein the length L of the whole vehicle is 4.6m, the width W of the vehicle is 20m, the height H of the vehicle is 1.4m, and the wheelbase B is 16 m;
(2) setting a calculation region omega, and setting the whole calculation region of the automobile external flow field as: omega 7L 7W 4H 325mX14.2mX5.7m, plane z 0m is a vehicle body symmetry plane, and the coordinate origin is located at the projection of the front end of the vehicle body on the ground;
(3) carrying out non-structural mesh subdivision on the calculation region omega, wherein the total number of non-tetrahedral meshes is about 1.2 multiplied by 10 after subdivision7The degree of freedom is about DOF 1.03 × 107The size of the grid near the vehicle body reaches millimeter level.
(4) Partitioning the calculation region, namely the discrete grid, so as to construct a proper preconditioner by using a region decomposition method;
(5) the fluid is air at 25 deg.C and quasi-atmospheric pressure, and its density rho is 1.185Kg/m3The kinematic viscosity coefficient mu is 1.183X 10-5Kg/m3Setting the inlet velocity Vin30t, time step ΔtCalculating the variation of the flow field in 1S when the variation is 0.01S, and carrying out wrong convergence on a linear solver and a non-linear solver in the algorithm to be 10-4And 10-6Respectively pick up mutAnd (3) calculating the Reynolds number, wherein the speed is 30m/s, the vehicle height H is 1.41m, and the characteristic length is:
preferably, the selection of the calculation region Ω in the step (2) is related to calculation problems, and must be large enough to avoid the influence of the region wall surface on the flow field outside the vehicle body as much as possible, and also consider the size of the whole calculation amount, and in addition, when mesh is subdivided, in order to ensure the calculation accuracy, the generated mesh needs to cover all the main surface features of the complex structure of the whole vehicle body, namely, the so-called envelope technique. The envelope technology is very important in the calculation of the external flow field and is the key point for realizing the calculation of the external flow field of the complex model. Therefore, the mesh often needs to be encrypted to a minimum on the surface of the vehicle body.
Preferably, the wake outlet boundary in the step (2) should be 5-10 times the vehicle height from the vehicle model established in the step (1).
Preferably, in the step (3), when the grid is divided, the areas, such as the wall surface of the vehicle body, which have a large influence on fluid movement, and the wake area, which have a close relationship with the aerodynamic analysis of the vehicle, are encrypted.
Preferably, the number of the grid partitions in the step (4) is equal to the number of the processors, and the number of degrees of freedom calculated by each partition is approximately the same to achieve load balancing.
Preferably, in the step (4), the mesh partition is performed by calling an open source software package ParMETIS.
Compared with the prior art, the invention has the beneficial effects that: setting a calculation region omega through the whole vehicle model structure, carrying out mesh subdivision and mesh partition, and then carrying out mistakenly convergence on a linear solver and a non-linear solver in the algorithm to obtain a relative convergence difference of 10-4And 10-6. Respectively take mutThe analysis method of the flow numerical value of the automobile external flow field maximizes, reduces the huge scale of numerical calculation, improves the accuracy of the numerical calculation, and has good parallel expansibility under the condition of thousands of core processors.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a technical scheme that: an analysis method for flow values of an automobile external flow field comprises the following steps:
(1) carrying out model construction by adopting three-dimensional CAD software according to full-size data of a certain real vehicle model, wherein the length L of the whole vehicle is 4.6m, the width W of the vehicle is 20m, the height H of the vehicle is 1.4m, and the wheelbase B is 16 m;
(2) setting a calculation region omega, and setting the whole calculation region of the automobile external flow field as: omega 7L 7W 4H 325mX14.2mX5.7m, plane z 0m is a vehicle body symmetry plane, and the coordinate origin is located at the projection of the front end of the vehicle body on the ground;
(3) carrying out non-structural mesh subdivision on the calculation region omega, wherein the total number of non-tetrahedral meshes is about 1.2 multiplied by 10 after subdivision7The degree of freedom is about DOF 1.03 × 107The size of the grid near the vehicle body reaches millimeter level.
(4) Partitioning the calculation region, namely the discrete grid, so as to construct a proper preconditioner by using a region decomposition method;
(5) the fluid is air at 25 deg.C and quasi-atmospheric pressure, and its density rho is 1.185Kg/m3The kinematic viscosity coefficient mu is 1.183X 10-5Kg/m3Setting the inlet velocity Vin30t, time step ΔtCalculating the variation of the flow field in 1S when the variation is 0.01S, and carrying out wrong convergence on a linear solver and a non-linear solver in the algorithm to be 10-4And 10-6Respectively pick up mutAnd (3) calculating the Reynolds number, wherein the speed is 30m/s, the vehicle height H is 1.41m, and the characteristic length is:
the selection of the calculation region omega in the step (2) is related to the calculation problem, and must be large enough to avoid the influence of the region wall surface on the flow field outside the vehicle body as much as possible, and also consider the size of the whole calculation amount, in addition, when the mesh is subdivided, in order to ensure the calculation accuracy, the generated mesh needs to cover all the main surface characteristics of the complex structure of the whole vehicle body, namely, the so-called envelope technology. The envelope technology is very important in the calculation of the external flow field and is the key point for realizing the calculation of the external flow field of the complex model. Therefore, the grid is often required to be encrypted to be extremely small on the surface of the vehicle body, and the wake outlet boundary in the step (2) is 5-10 times the vehicle height from the vehicle model established in the step (1).
In the step (3), when the grids are divided, areas such as a vehicle body wall surface and the like which have a large influence on fluid movement and a wake area and the like which have a close relation to the pneumatic analysis of the automobile are encrypted.
The number of the grid partitions in the step (4) is equal to the number of the processors, the number of the degrees of freedom calculated by each partition is approximately the same so as to achieve load balance, and the grid partitions are performed by calling an open source software package ParMETIS in the step (4).
Setting a calculation region omega through the whole vehicle model structure, carrying out mesh subdivision and mesh partition, and then carrying out mistakenly convergence on a linear solver and a non-linear solver in the algorithm to obtain a relative convergence difference of 10-4And 10-6. Respectively take mut30m/s, and a vehicle height H1.41m is the characteristic length, calculates the Relo number, and the analysis method of the flow numerical value of the automobile external flow field maximizes, reduces the huge scale of numerical calculation, improves the accuracy of the numerical calculation, and has good parallel expansibility under the condition of thousands of core processors.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (6)
1. The method for analyzing the flow numerical value of the automobile external flow field is characterized by comprising the following steps of:
(1) carrying out model construction by adopting three-dimensional CAD software according to full-size data of a certain real vehicle model, wherein the length L of the whole vehicle is 4.6m, the width W of the vehicle is 20m, the height H of the vehicle is 1.4m, and the wheelbase B is 16 m;
(2) setting a calculation region omega, and setting the whole calculation region of the automobile external flow field as: omega 7L 7W 4H 325mX14.2mX5.7m, plane z 0m is a vehicle body symmetry plane, and the coordinate origin is located at the projection of the front end of the vehicle body on the ground;
(3) carrying out non-structural mesh subdivision on the calculation region omega, wherein the total number of non-tetrahedral meshes is about 1.2 multiplied by 10 after subdivision7The degree of freedom is about DOF 1.03 × 107The size of the grid near the vehicle body reaches millimeter level.
(4) Partitioning the calculation region, namely the discrete grid, so as to construct a proper preconditioner by using a region decomposition method;
(5) the fluid is air at 25 deg.C and quasi-atmospheric pressure, and its density rho is 1.185Kg/m3The kinematic viscosity coefficient mu is 1.183X 10-5Kg/m3Setting the inlet velocity Vin30t, time step ΔtCalculating the variation of the flow field in 1S when the variation is 0.01S, and carrying out wrong convergence on a linear solver and a non-linear solver in the algorithm to be 10-4And 10-6Respectively pick up mutAnd (3) calculating the Reynolds number, wherein the speed is 30m/s, the vehicle height H is 1.41m, and the characteristic length is:
2. the method for analyzing the flow values of the external flow field of the automobile according to claim 1, wherein the calculation region Ω in the step (2) is selected in relation to the calculation problem, and must be large enough to avoid the influence of the region wall on the external flow field of the automobile as much as possible, and also take into account the overall calculation amount, and in addition, when the mesh is divided, in order to ensure the calculation accuracy, the generated mesh needs to cover all the main surface features of the complex structure of the whole automobile body, namely, the so-called envelope technique. The envelope technology is very important in the calculation of the external flow field and is the key point for realizing the calculation of the external flow field of the complex model. Therefore, the mesh often needs to be encrypted to a minimum on the surface of the vehicle body.
3. The method for analyzing the flow value of the automobile external flow field according to claim 1, wherein the wake outlet boundary in the step (2) is 5-10 times the height of the automobile model established in the step (1).
4. The method for analyzing the flow value of the automobile external flow field according to claim 1, wherein in the step (3), when the grid is divided, areas such as a wall surface of the automobile body and the like which have a large influence on the fluid movement and a wake area and the like which have a close relationship with the automobile pneumatic analysis are encrypted.
5. The method for analyzing the flow value of the out-of-vehicle flow field according to claim 1, wherein the number of the grid partitions in the step (4) is equal to the number of the processors, and the number of the degrees of freedom calculated by each partition is approximately the same to achieve load balancing.
6. The method for analyzing the flow values of the out-of-vehicle flow field according to claim 1, wherein in the step (4), the grid partitioning is performed by calling an open source software package, ParMETIS.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113178003A (en) * | 2021-04-26 | 2021-07-27 | 杭州新迪数字工程系统有限公司 | Automatic flow field extraction method based on 3D model |
| CN113392568A (en) * | 2021-08-17 | 2021-09-14 | 北京航空航天大学 | Load balancing method of dynamic calculation domain in aircraft aerodynamic characteristic parallel simulation |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113178003A (en) * | 2021-04-26 | 2021-07-27 | 杭州新迪数字工程系统有限公司 | Automatic flow field extraction method based on 3D model |
| CN113392568A (en) * | 2021-08-17 | 2021-09-14 | 北京航空航天大学 | Load balancing method of dynamic calculation domain in aircraft aerodynamic characteristic parallel simulation |
| CN113392568B (en) * | 2021-08-17 | 2021-10-29 | 北京航空航天大学 | Load balancing method of dynamic calculation domain in aircraft aerodynamic characteristic parallel simulation |
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