Optimization Of Drag Reduction Of Automobile Tail Structure Based On Approximate Model

China,as the world’s largest country in terms of vehicle ownership,is increasingly important in reducing oil consumption and developing electric vehicles,and will rise to the national strategic level.In the method of reducing fuel consumption,one of the most effective methods is to reduce the air resistance coefficient of a car.In China,tens of millions of new vehicles are added every year,so reducing the aerodynamic drag of the car and optimizing the entire drag reduction process are imminent.This paper takes the back-end MIRA model as the research object,and adopts the approximate optimization method to optimize the drag reduction of the automobile’s tail structure.For multi-dimensional and complex optimization problems,the combination of the approximate model and the optimization algorithm is highly efficient and accurate.The main purpose of the dissertation is to build an optimization system to reduce the aerodynamic drag of the MIRA model by means of 3D modeling,computational fluid dynamics,and approximate optimization.The combination optimization is proposed and applied to the rear-end MIRA model rear-end structural parameter optimization to effectively improve the aerodynamic performance of the car.Firstly,the MIRA sedan model was established in the three-dimensional modeling software CATIA.Based on the simulation software of commercial fluid dynamics,the numerical simulation was carried out.It was found that the turbulent structure at the rear of the automobile is very complex and accompanied by great energy dissipation.Based on the above simulation results,the key factors that caused the greater resistance of the model were analyzed,and the roof inclination,rear taper,tail upturn angle,the chord length of the side profiles of the car body,the rear windscreen inclination,and the sidewindow inclination were selected.The tilt of the trunk lid has a total of seven parameter variables that have a large influence on the vortex area at the rear of the car.Because the parameters of the three parameters of the car body on both sides of the external cable chord length,side window inclination angle and roof inclination angle will cause the size of the front projection area of the car,and according to the calculation formula of the aerodynamic resistance,the change of the front projection area and the drag coefficient is known.Will cause aerodynamic drag changes.Therefore,it is no longer reliable to use the aerodynamic drag coefficient as an evaluation index for aerodynamic performance optimization.Therefore,the product-streamline coefficient of the aerodynamic drag coefficient and the front projection surface is used as the evaluation index of the aerodynamic performance,and the tail structure of the MIRA model is optimized.Then,two different combinations of different approximation models and optimization algorithms are performed to analyze the effect of different combinations on the optimization of the objective function,and the error of the optimal solution and the simulation value of each group is verified.Considering the efficiency of each optimization combination synthetically,under the conditions of different conditions,the optimal combination of engineering problems for the optimization of automobile modeling is not exactly the same.Finally,the optimization of the seven parameter variables reduced the streamlined coefficient of the vehicle by 16.9%.According to the DOE matrix,the influence degree of each key parameter on vehicle resistance,and the fitting function relationship between each parameter and drag coefficient and streamlined coefficient were analyzed.The simulation of the model corresponding to the optimal parameters was carried out,and the post-processing of the simulation results was analyzed to analyze the flow field in the rear of the vehicle.It was compared with the MIRA model to study the mechanism of drag reduction.The optimization process designed in this paper not only quickly and effectively analyzes the influence of various parameter variables on the aerodynamic drag of the vehicle,identifies key parameter variables,optimizes the design process,reduces the aerodynamic drag of the car,and saves a lot of time and effort.The actual process of automotive design has a certain reference value,while providing a reference for the optimization of automotive aerodynamic shape design.