A Research On Drag Reduction Control Strategy Based On Automobile External Flow Field

With the development of society and the improvement of people’s living standards,the number of cars in China is increasing year by year.The total number of cars in China has reached 260 million in 2019,and it is expected that it will continue to grow in the future.The continuous development of the automotive industry has also brought about social problems such as increasing energy demand and increasing environmental pollution.Improving the aerodynamic characteristics of automobiles is of great significance for improving the fuel economy of automobiles.The main energy of the automobile is used to overcome the driving drag.The driving drag of the automobile includes mechanical drag and aerodynamic drag.As the speed of the car increases,the proportion of aerodynamic drag will also increase.When the car is driving at a high speed,the aerodynamic drag of the automobile will be the main source of the car’s driving drag.Reducing the aerodynamic drag of the automobile driving at a high speed can save more fuel and increase the mileage.In this paper,the Ahmed model and GTS(Ground Transportation Systems)model as the research objects.According to the characteristics of the external flow field of the automobile model,the tail and top drag reduction devices were innovatively designed to control the external flow field of the car.Drag reduction mechanism of additional devices were also studied.The main research work includes:(1)In the hybrid RANS/LES mode,the IDDES model based on SST k-ω is used to numerically simulate the external flow field of the Ahmed simplified small car model,and the complex three-dimensional wake flow field structure is predicted.Using the IDDES model based on Transition SST to numerically simulate the external flow field of the GTS simplified large truck model,the transition and turbulence characteristics at the top are predicted.Compared with the single RANS or LES mode,while maintaining the calculation efficiency and calculation accuracy;(2)According to the wake structure of the Ahmed model,vortex generators and riblets are designed on the slant and rear to influence the pressure drag and friction drag.The add-on device of the Ahmed model achieves a maximum drag reduction of 6.21%.On this basis,combined control strategies different from the traditional single device is designed to achieve the synergistic drag reduction effect of additional devices,maintain the decrease in pressure drag and friction drag,and further increase the drag reduction to 8.62%;(3)According to the structural characteristics of the GTS model length,two additional devices,cylindrical and convex,are designed in the top region.By making the flow advance into turbulence and reducing the effect of turbulence at the tail,achieve a drag reduction effect of up to 5.94%.On this basis,two aspects such as pressure drag and friction drag,turbulent development and dissipation of additional devices are analyzed.The structural parameters of additional device were optimized to increase the drag reduction to 6.91%.