Research On Wake Control And Drag Reduction Of MIRA Model Based On Plasma

With the development of industry,automobiles have become the most important means of transportation for the public.The increase in fuel prices has made the competition in the automobile market more intense.Automotive aerodynamics are playing an increasingly important role in automotive design.So far,there have been abundant studies on improving the aerodynamic characteristics of automobiles.In terms of drag reduction,methods such as changing the shape of the car and adding aerodynamic kits have been very common,but these methods belong to passive drag reduction research,while active reduction there are few researches on resistance.Plasma flow control is an active flow control technology based on the new concept of plasma pneumatic excitation.It generates a strong electric field by setting electrodes on the surface of the control object,which ionizes the air to generate plasma on the one hand,and accelerates the plasma on the other hand,so that the plasma collides with the neutral gas,thereby transferring momentum and achieving the purpose of controlling the fluid.As a relatively cutting-edge technology in the field of active flow control,it has attracted the attention of researchers and scholars from all over the world because of its advantages of no moving parts and fast response.This paper is based on the basic principle of plasma flow control,by installing the plasma exciter in different positions of the MIRA model,and changing the flow velocity,excitation voltage,number of exciters and the spacing of the exciters to calculate,the results are obtained under different working conditions.In order to using plasma exciter to improve the aerodynamic characteristics of automobile,the effect of plasma exciter on aerodynamic resistance and the control effect of plasma excitation on vehicle wake is revealed.The specific research contents are as follows:Firstly,the geometric model of SDBD plasma exciter is established,after completing the pretreatment,determining the physical model and boundary conditions,the calculation and benchmarking are carried out to verify its accuracy,then the mathematical model of plasma excitation is obtained;Secondly,the half-car model of 1/4 MIRA is established.In the case of no exciter,the steady-state simulation of the original model is completed,and the transient calculation is carried out on the basis of the steady-state results to obtain its aerodynamic characteristics results.Then post-processing analysis such as pressure distribution and velocity distribution is carried out,and the resistance coefficients are compared with the experimental results,so strategies such as grid parameters,boundary conditions,and solution setting parameters are determined;Then the plasma exciter is added to the original model to change the flow velocity,excitation voltage,installation position of the exciter,the size of the exciter,the number and the distance of the exciter(exciter array)are calculated to explore the effect of the plasma exciter in controlling the airflow separation at the rear of the vehicle and the aerodynamic resistance of the vehicle under different working conditions;Finally by comparing the results and analyzing the effect and mechanism of plasma control on vehicle wake flow separation and aerodynamic resistance to obtain the effect of plasma excitation on vehicle aerodynamic characteristics.Through numerical calculation and analysis,the following conclusions are drawn:(1)The control effect of a single plasma exciter on low-speed incoming flow is better than that of high-speed incoming flow.And there is no proportional relationship between the exciter control capability and improving the aerodynamic characteristics of the vehicle.For different inflow speeds,there is an optimal excitation voltage value corresponding to the aerodynamic characteristics of the vehicle.(2)Plasma excitation will have different effects at different positions,but its control ability and control range are limited,and it can only have a relatively obvious effect on a part of the flow field at the rear of the exciter installation.In the far area,there is little effect.(3)Under the combined control of the exciter,there is a certain interaction between the four positions A,B,C,and D,and the induced airflows generated by them influence each other,thereby jointly changing the wake structure of the car.(4)Under the control of the exciter array,appropriately increasing the number of exciters is beneficial to reduce the aerodynamic drag coefficient,but the effect is not significant,and when the number of exciters increases to a certain number,there is almost no additional drag reduction effect.So the work should be comprehensively considered efficiency issues to choose the right number of exciters.