Flow Field Characteristics Within Non-smooth Surface Boundary Layer On Car-body And Aerodynamic Drag Reduction Analysis Under Crosswind

With the continuous development of the automotive industry and constantly improvement of the highway network, the actual car traveling speed is greatly improved, which will greatly affect the car’s aerodynamic drag. The greater the travel speed, the greater the aerodynamic drag, aerodynamic drag reduction means lower fuel consumption. With the development of vehicle aerodynamics, the traditional method of reducing the aerodynamic drag of the vehicle body is mature and are experiencing technical bottleneck period, new aerodynamic drag reduction methods and ideas are needed. Study at home and abroad found bionic non-smooth surfaces with good drag reduction affect, therefore non-smooth structure can be introduced into an automobile body, making the vehicle low-drag and energy-saving.This paper is based on the standard stepped back MIRA model, the pit-type non-smooth surface is located at the top surface of the car-body. Changes of key flow field parameters within the boundary layer near the top surface and the impact of these changes on wake flow and the drag reduction mechanism are analyzed. Final ly, pit-type non-smooth structure’s drag reduction effects under crosswind state and the impact on vehicle traveling are further studied.Firstly, shape, size and layout position of the pit-type non-smooth unit is confirmed to establish non-smooth body model. CFD numerical simulation method is used for smooth and non-smooth car model simulation, and by comparison with the wind tunnel experimental result of MIRA model to verify the numerical simulation’s reliability.Secondly, the flow field characteristics within the non-smooth surface boundary layer is studied, changes in airflow velocity, boundary layer thickness, wall shear stress, surface friction and the impacts upon the wake flow state after the boundary layer separation, turbulence intensity, turbulen ce dissipation rate are analyzed to explore the mechanism of drag reduction of non-smooth structure.Finally, steady state numerical simulation under crosswind state is used to comparative analysis of flow field features around the smooth and non-smooth car model within the range of 0~30 °(yaw angle increases by 3 °). Coefficient of aerodynamic and aerodynamic were calculated and the impacts of the introduction of non-smooth structure on aerodynamic characteristics especially on the aerodynamic drag under crosswind state is analyzed based on the external flow field velocity, pressure, turbulent kinetic energy distribution.