The Influence And Optimization Of Vehicle’s Rear Shape For Aerodynamic Drag Reduction Of Pit Type Non-smooth Body

With the constant improvement of the domestic highway system, the continuousdevelopment of auto industry, and the gradual decrease of the world’s oil resources,cars will develop more faster and more economic. Automotive speed affect theaerodynamic drag, the faster the car, the greater the aerodynamic drag. Fuel power thatair resistance consumed is proportional to the cube of car’s velocity, so the automotiveair resistance directly affect the car’s fuel economy. The decrease of aerodynamic dragmean the reduction of fuel consumption, which can achieve energy conservation andenvironmental protection. With the development of aerodynamics, the traditionalmethod of reducing the aerodynamic drag has some technical bottleneck, it is imminentand necessary to seek new aerodynamic drag reduction method. The study found thatthe bionic non-smooth surface has good drag reduction effect, according to the thoughtof drag reduction, the non-smooth structure can be put on the car body to achieve dragreduction and energy saving.This paper is based on the MIRA model group with different rear shape, study theinfluence of different rear shape on non-smooth drag reduction effect by introducingpit type non-smooth structure on the vehicle rear end surface, and optimize thenon-smooth surface, improve the drag reduction performance, finally combinepassive drag reduction of non-smooth with active drag reduction of eddy effusion torealize optimized combination of the two types.CFD simulation analysis is the critical step in the paper, firstly set up MIRAmodel group with different rear shape，and the pit type non-smooth surface wasarranged in the vehicle rear end of models，analyzed the wake structure of threedifferent models. Through external flow field numerical calculation, and combinedwith wind tunnel test,compared the smooth model and non-smooth model’s tail flowfield, pressure, and the turbulent kinetic energy, and compared non-smooth surfaceflow difference of different vehicle’s rear shape.Then based on straight back model, analyzed the aerodynamic drag reductioneffect of pit-type non-surface rectangular array, set rectangular arrangement andnon-smooth unit body as optimization objective, and used the Latin Hypercube methodto select sample data. The response values corresponding to the sample were achievedby CFD simulation, the Kriging model was established. The credibility of the model was verified and global optimization was carried out by optimization algorithm. Theoptimized non-smooth surface can improve aerodynamic drag reduction effect andimprove wake structure. On the base of optimized result, analyzed the influence ofnon-smooth surface on reduction of aerodynamic drag, and also explained differentdrag reduction rate of three models for different reasons, provided theory basis forfurther researching.Finally on the basis of non-smooth straight back model，a vortex generator withvariable jet velocity is equipped in the pit array to control rear air flow of model,improving the trailing vortex structure. Through three models’(smooth model,non-smooth model, non-smooth model with eddy injection) numerical simulation ofthree dimensional flow field，some parameters（such as airflow velocity, pressure, andthe turbulent kinetic energy）of models with different tail morphological characteristicsare obtained，the difference of aerodynamic drag coefficient of different models underdifferent wind speed and the drag reduction effect under different jet velocity arecompared, changes of tail flow field parameter are analyzed, aerodynamic dragreduction mechanism and the effect of eddy-jet agitation of non-smooth body areelaborated, a optimized combination which consists of passive drag reduction of thenon-smooth form and active drag reduction of eddy effusion is realized, and theaerodynamic drag of MIRA Straight back model under different speed is effectivelyreduced.This article studied and analyzed the tail non-smooth surface’s aerodynamic drageffect on different models, and optimization design of the aerodynamic effect wascarried out for straight-back model, good drag reduction effect is obtained. On thebasis of non-smooth passive drag reduction, by using the active drag reduction methodof eddy effusion, provides new method for the aerodynamic drag reduction with acertain degree of guidance.