The Near Wall Flow Field Simulation Method Improvement Research For The Non Smooth Surface Of Vehicle Body

In the social background of energy crisis and environmental protection demands,the requirement of air drag reduction is increasing and the technology is also developing.The traditional method of automobile drag reduction mainly includes shape optimization technology,accessory installation,active control.However,the above technology has already matured,so it is urgent to research the new drag reduction method.Natural creatures have already evolved for millions years and have have so many advantages that we can't match.Bionics research has found that some organisms' non smooth feature can change the flow field characteristics,which can play a good aerodynamic drag reduction effect.However,the application of the above bionic nonsmooth features while greatly improve the difficulty of automobile aerodynamic simulation.Because it while increase the difficulty of modeling and also increase the number of simulation mesh.In the simulation process,the wall function can use empirical formula to simulate the law of the wall flow field,so the bionic non smooth wall function can effectively solve the above problems.This paper is to study the non smooth work effect on flow field to build a new bionic non smooth wall function to improve the efficiency of simulation.Using large eddy simulation method to study the wall flow field.First,verified the effectiveness of the large eddy simulation method by the case of flow around cylinder case.while using large eddy simulation,the choice of discrete scheme has an important influence on the accuracy of simulation results.Using different discrete schemes to simulate the flow field of the Dshap model found that adopting upwind discrete scheme is easier to converge than adopting center difference discrete scheme,but the error of simulation results is large.Combined with the above two discrete schemes to build new discrete scheme.The mathematical analysis shows that the new discrete scheme has better convergence,and the simulation results also show that the new discrete scheme can reduce the numerical fluctuation to improve the convergence and have a good simulation accuracy.Therefore,it can be shown that the new discrete scheme can have a better accurate simulation result on the premise of reducing the number and quality of mesh.Using Dshap model to study the non-smooth elements work effect on the wall flow field.Setting a series of cases by applying different depths and densities pits on the surface of the Dshap model.Using large eddy simulation method to research the wall flow field of different non-smooth model.The results show that the non-smooth elements will increase the wall shear stress,and then change the Y+ value of near wall flow field.Compared with the smooth model the Y+ value of the non-smooth model will increase,and the increase is proportional to the distance from the wall.These changes will lead to the thinner boundary layer of the wall non-smooth model,and then affect the whole flow field of the model.Extracting the size parameters of the non-smooth element,using the parameters to study the change rule of near wall flow field.Using MATALAB to fit the wall flow field change rule formula.Analysis OpenFOAM standard wall function,integrated the fitting formula and standard wall function to form non-smooth wall function.Verified the effectiveness of the non-smooth wall function by compared with the wind tunnel test results.Therefore,the non smooth wall function can effectively replace the real physical modeling of the non-smooth wall,only need to input different parameters can achieve different non-smooth wall flow field simulation,which can effectively improve the simulation efficiency.