Study On Mesh Size Control For Numerical Simulation Analysis Of Flowfield Based On A Vehicle

With the continuous improvement of people's living standards and the rapid development of infrastructure such as national roads and bridges,automobiles have become the main vehicle in people's daily life.By the end of June 2018,the number of automobiles in China had reached 319 million,which has caused a shortage of energy.So how to reduce the fuel consumption of automobiles has been a research hotspots.However,reducing the drag coefficient is an important way to reduce fuel consumption of automobiles.While the external flow field study is very important for the reduction of automobile drag coefficient.At present,the main research methods of automobile external flow field are wind tunnel test and numerical simulation.For the wind tunnel test method,which has the disadvantages of high cost and long period.With the development of computer technology and the improvement of turbulence models,computational fluid dynamics(CFD)has been used in automobile external flow study.However,the main focus fields in the study of numerical simulation of automotive external flow field are solving equations,solving methods,turbulence models and grid types,while the researchs on grid generation methods are less.In this paper,grid partition control technology,a new grid generation method,has been creatively put forward.According to the characteristic size of geometric surface and the contribution of components in the analysis of external flow field,different grid sizes are used for different parts of automobile.The application of this technology aims at reducing the number of grids and computing time on the premise of ensuring the convergence and accuracy of simulation.And four different meshing forms(pure tetrahedron,mixed tetrahedron,trimmer and polyhedron)are used to verify the applicability of different meshing methods in automobile external flow field.The results show that under the same mesh size and mesh partition control conditions,the calculation results of trimmer mesh are closest to the experimental results,and which also have the advantages of fewer meshes,higher mesh quality and shorter computing time.In this paper,Realizablek-?model has been used in the simulation,which has high accuracy and less computer resources occupation.Combining with grid partition control technology and trimmer volume mesh,the simulation result is highly consistent with the experiment result in Jilin Universityautomobile wind tunnel.The deviation of drag coefficient is less than 1.6%,and the deviation of surface pressure is below 10%,which indicate that the result of simulation has a high accuracy.In this paper,the grid partition control technology and the selection of grid type and turbulence model has been proposed,which can improve the accuracy of the simulation results of vehicle external flow field,and save a lot of computing resources and time of simulation.And the relationship between pressure field,velocity field,turbulent kinetic energy and surface structure of automobile is analyzed and summarized,which provides effective theoretical support for further reducing drag coefficient.This technology provides a certain guiding for improving the efficiency of research and design optimization and shortening the development cycle of automobile.