Analysis And Optimization On The Drag Reduction Of The Vehicle With Non-smooth Surface In Different Arrangement

With the rapid development of Chinese automobile industry,the consumption of vehicle fuel increases rapidly.More and more attention has been paid to the fuel economy of automobiles.At present,the actual speed of automobile is increasing constantly,and the consumption of 100 km fuel used for aerodynamic resistance is proportional to the square of vehicle speed.Therefore,reducing the aerodynamic resistance of automobile is an important way to improve its fuel economy.However,with the continuous improvement of automobile aerodynamic shape,the research of body aerodynamic drag reduction has gradually entered a bottleneck period,and the rapid development of nonsmooth surface drag reduction technology provides a new research direction.In this paper,the phyllotaxis theory in biology is introduced into the arrangement design of the nonsmooth surface of the body,and compared with the rectangular arrangement which is the best drag reduction effect in the conventional arrangement.The drag reduction analysis and optimization are carried out to explore the optimal structural parameters for obtaining better effect on aerodynamic drag reduction.In this paper,based on squareback MIRA model,using the method of computational fluid dynamics(CFD),different boundary layer meshing schemes are studied combined with existing wind tunnel test data to improve the accuracy of numerical simulation.Selecting dimpled non-smooth surface as the research object,the phyllotaxis theory is introduced into the arrangement design of the dimple element,and the dimpled nonsmooth surface with rectangular arrangement and phyllotactic arrangement are arranged respectively on the rear surface of the car.The influence of two kinds of non-smooth surface on aerodynamic drag reduction is calculated by numerical simulation.Furthermore,according to the post-processing results of aerodynamic drag values,pressure field,friction coefficient of body surface,airflow velocity in the rear of body and turbulent kinetic energy of smooth model and non-smooth model,the influence of two kinds of non-smooth surface on the external flow field of squareback MIRA vehicle is analyzed.The non-smooth surface with phyllotactic arrangement shows better drag reduction performance in the comparison of the simulation results and the analysis of the parameters of the flow field.Considering that the drag reduction effect of the dimpled non-smooth surface has a great relationship with the geometric dimension of the unit,the optimization method based on the approximation model is adopted to optimize the design of the dimpled non-smooth surface with rectangular arrangement and phyllotactic arrangement respectively.The maximum drag reduction rates after optimization were 5.2% and 6.57%,respectively.Finally,the aerodynamic characteristics such as aerodynamic drag values,pressure field,friction coefficient of body surface,airflow velocity in the rear of body and turbulent kinetic energy of the two non-smooth surfaces before and after the optimization were compared,and the reliability of the optimization results is proved.In addition,based on the comparison of drag reduction rates and flow field parameters after optimization of two arrangement types of non-smooth surfaces,it is proved that the aerodynamic drag reduction performance of phyllotactic arrangement is better.In this paper,different boundary layer meshing schemes are studied to improve the numerical calculation accuracy of aerodynamic drag coefficient.On the basis of this,the drag reduction optimization of dimpled non-smooth surfaces with rectangular and phyllotactic arrangement are carried out,respectively.The better drag reduction performance of the phyllotactic ordering arrangement is proved through the comparison of the optimization results,which provides an effective reference for the application of the phyllotactic theory in the drag reduction of the body with non-smooth surface,and also provides a theoretical basis for the arrangement design of the non-smooth unit.