Synergistic Reduction Mechanism On Aerodynamic Drag And Noise Via Bionic Non-smooth Autobody

The continuous development of automobile aerodynamic drag reduction technology is to meet the energy consumption demand caused by the rapid growth of automobile consumption.The aerodynamic noise caused by the interaction of the vehicle with the air at high speed also has a great influence on the ride comfort of the occupant.The development of bionic non-smooth aerodynamic drag reduction and noise reduction technology based on bionic is progressing rapidly,which produces a positive aerodynamic drag reduction noise reduction effect.This paper is based on the bionic basic method and the aerodynamic boundary layer theory of engineering bionics to study on mechanism of synergistic aerodynamic drag and noise reduction with the experimental research and numerical simulation.The wind tunnel test standard Driv Aer model is selected to simulate the reliability of CFD simulation method.In the steady-state calculation stage,the accuracy of two RANS steady-state models is analyzed by using the pressure coefficient distribution diagram of Driv Aer model.Both models have over-predicted the transition point of the laminar boundary layer at the top of the vehicle.In the transient calculation stage,the LES model is used to calculate the body pressure coefficient distribution and the wake structure of fast trailing Driv Aer model,and the results are consistent with the wind tunnel test data.With reference to the literature,the bionic non-smooth structure is established at the rearview mirror and the upper surface of Driv Aer model.The influence of non-smooth surface on the flow field and sound field of boundary layer is analyzed and compared after the calculation of aerodynamic drag and aerodynamic noise,and the influence and mechanism ofnon-smooth structure on vehicle air drag reduction and noise reduction are revealed.The results show that the non-smooth structure affects the transition of the laminar boundary layer to the turbulent boundary layer when the bionic non-smooth structure is applied at the rear-view mirror,which affects the rearview mirror wake and the turbulence boundary layer within the air separation point lag,the speed gradient of the turbulent boundary becomes larger.Rear view mirror wake structure has a forward side of the window outside the normal direction and downward trend with energy dissipation.All of these contribute to the reduction of aerodynamic drag and noise.The bionic non-smooth structure on the upper surface of the vehicle body also has an influence on the laminar boundary layer of the roof of the vehicle body,which leads to the transition of the laminar boundary layer to the turbulent boundary layer.The thickness of the turbulent boundary layer increases,but the friction coefficient and shear force decrease at the top cover and the pulsating pressure of the local airflow decreases.The turbulence dissipation rate increases with the increase of the turbulence dissipation rate,the turbulent kinetic energy concentration zone and the turbulent dissipation area decrease and move down,which contributes to the reduction of drag coefficient.The use of bionic non-smooth structure in the body of the two places has played a good aerodynamic drag and noise reduction effect.The low-speed eddy with high-energy produced by the non-smooth structure affects the local laminar boundary layer transition and stabilizes wake structure,reduces the pulse pulsation,reduces the energy loss of the air flow through the vehicle body.The exploration of the mechanism of bionic non-smooth body synergistic aerodynamic drag reduction and noise reduction has important engineering reference significance for automobile modeling and NVH design.