Experimental and numerical studies are performed to evaluate and analyze the influence of the notchback rear diffuser angle on aerodynamic drag and wake structure. The relationship between aerodynamic drag and rear diffuser angle is summarized, and the flow mechanism are analyzed and discussed. A speculation regarding lower trailing vortices is proposed, and is verified in the present research model. Rear diffuser angle is an important factor influencing the wake structure, and optimizing the vehicle rear diffuser at a favorable angle can contribute to reduce the drag force and improve the wake structure.
Active flow control of surface dielectric barrier discharge (SDBD) plasma is a technology that converts electrical energy into kinetic energy to achieve flow control. Its main application areas are concentrated in the aviation field. Undoubtedly, few studies have applied it in the field of automobile flow control. Meanwhile, during high-speed driving, there is a serious airflow separation phenomenon at the rear of notch-back cars, which brings a large area of negative pressure to the back of the cars. Due to the huge pressure difference between the front and end of the cars, it will increase the driving drag and fuel cost of the car. In this context, we seek to discuss the control effect on the airflow separation at the rear of the notch-back by using the phenomenological numerical simulation method of plasma flow control. Firstly, the plasma actuator is arranged separately on the rear end of the roof, c-pillar, upper and side of the trunk to study the control effect of airflow separation. After that, the plasma actuators at each position are combined and actuated simultaneously. We try to observe the control effect of airflow separation and select the combination with the best drag reduction effect. In the third stage, an efficient global optimization (EGO) algorithm based on kriging response surface is applied to optimize the supply voltage of the best combination that has been obtained before and obtain the driving voltage parameter of each actuator optimized under this combination. The results show that when plasma actuation is applied at four locations, only the actuation applied to the side of the luggage compartment has a significant drag reduction effect, while in other cases, the drag coefficient will increase. Specifically, drag reduction is better when the actuation is applied at four positions simultaneously. The maximum drag reduction coefficient of the car is reduced by 13.17%.
An aerotrain model containing wings with variable angles of attack and positions is constructed. Numerous wind tunnel experiments are conducted to research the influences of angles of attack and relative positions of the wings on the aerodynamic performances of the aerotrain. Experimental results show that the influence of relative positions is insignificant in contrast to that of angles of attack. A long distance between the front and rear wings indicate good aerodynamic performance. The long distance can increase the lift coefficient of the model but has little influence on the drag coefficient. Two representable wing location conditions are selected to measure the pressures on the wing surface. The distribution curves of the wing surface pressures are obtained. The relationship among wing surface pressures, angles of attack, and locations is determined. Flow visualization experiments are conducted on two conditions, and the flowing law on the upper surfaces of the front and rear wings is identified.
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