| This paper studies the characteristics of the airflow around the van-body truck and its effects on the aerodynamic drag by means of theoretical analysis, experimental investigation and numerical simulation. It also offers rich information of the flow field around the van-body truck as well as useful data for the design of the outside aerodynamic shape of the van-body truck.The van-body truck is a blunt body with irregular shape. This paper first deals with many problems in experimental technique whose solutions are prerequisite for performance experiment on aerodynamic characteristics in a mini-type aviation wind tunnel of 1-meter magnitude. Investigation shows that Reynolds number, the similarity parameter of the van-body truck model experiment in the wind tunnel, need not be as large as that of a real operating full-size truck. The Reynolds number will do as long as it is in the range of automatic modeling of the experimental graph and the critical value is Re=0.5xl06(width of the truck is characteristic length). As the bottom of the van-body truck is considerably high, the influence of the ground boundary layer can be ignored in the wind tunnel simulation of ground effect. By extending length of the test floor properly, the aerodynamic drag coefficient can be measured more precisely. The blockage ratio of experiment on automobile model is allowed to be as high as 13.2% in the opening wind tunnel. Based on experiments, this paper presents the concept of critical length of the van-body truck model. Given a certain proportion, the length of the model, if it exceeds the critical length, can be changed to the latter, which will better satisfy the testing conditions of the mini-type wind tunnel. Experimental investigation also shows that the critical length for the van-body truck model in 1:10 scale is 1.4 meters.Numerical simulation and experimental research show that, when air flows over the surface of the truck, around the head of it there exists a positive pressure area which is a main contributor to the pressure-difference drag of the truck. The airflow around the top of the truck is induced into separation at the upper-fore verge of the driver cab. Then a vortex region is formed over the driver cab. The vortex in the region interacts with the positive pressure area on the front side of the van, affecting the aerodynamic drag characteristics when there is change in the van height or the gap between the driver cab and the van. As a result, the relationship between the change in aerodynamic drag coefficient and that in the gap or the height is complicated. There is a best gap for a certain van height and vice versa. The rear of the van-body truck, with an abruptly cut shape, where intricate tail-vortex system exerts stronger negative pressure, is also a main area contributing to pressure-difference drag of the truck.Research shows that wind deflector installed on a van-body truck can reduce aerodynamic drag considerably as well as decrease fuel consumption. In addition, the deflector can increasecritical Reynolds number of the aerodynamic drag coefficient graph. Proper design of the gap between the deflector bottom and the top of the driver cab can enhance the effect of the deflector in reducing drag. A vortex regulator installed at the rear of the truck can reduce airflow energy consumption in the tail-vortex region, causing the static pressure to rise again and thus lessening the pressure-difference drag.In our research, a 3-D numerical simulation calculation of the outside flow field of the flat-headed van-body truck has been made first. A RNG k-?turbulence model which can increase the calculation precision of the separation flow has been adopted, and the results show that the calculation of the van-body truck with the RNG k-e turbulence model is more exact than that of the standard k-e turbulence model.This paper presents a mathematical model that employs momentum method to calculate the aerodynamic drag of the truck. This model achieves higher precision than previous methods without consi...
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