| In this paper, the drag reduction issues on the vans were explored by means of a combined method with theoretical analysis, numerical simulation and wind tunnel simulation experimental study, from the perspectives of decreasing surface frictional resistance and pressure drag before and after on the van body respectively, studying the effects on the aerodynamic drag by two different drag reduction methods with air film drag reduction and install tail domes on the vans. Aimed at the mechanism of air film drag reduction, three kinds of drag reduction theories, including the thickened boundary layer theory, the mixed deceleration theory, the thickened boundary layer-mixed deceleration theory were proposed respectively,and the friction resistance calculation model of the van body surface were established under the condition of each theory. This paper explored the effects of frictional resistance on the van body surface with different parameters of air film thickness, different relative thickening quality, and the interaction of the two. In addition, combined with CFD simulation, this paper analyzed the effects and trends of frictional resistance on the van body surface with different factors such as the diameters of holes, the inclination of holes, the longitudinal spacing of holes, the lateral spacing of holes, as well as different mainstream velocities and jet velocities, and verified by the wind resistance test experiments. In order to solve the problem of how to reduce pressure drag on the van body, this paper took the drag reduction method of installing tail domes to achieve pressure drag reduction. At first, three different types of tail domes were designed, and the influence on pressure drag of these tail domes were investigated by CFD simulation, and got the size of tail dome with the best drag reduction effect, and then verified the effectiveness and feasibility of the tail domes drag reduction by the wind resistance test. The main contents of this paper are as follows:Firstly, this paper completed the research and development of a variable wind resistance test device. According to the needs of project research,a variable wind resistance test device was designed and manufactured, which provides an experimental platform for the subsequent simulate wind resistance tests.Secondly, on the basis of fluid boundary layer theory, the thickened boundary layer theory, the mixed deceleration theory, the thickened boundary layer-mixed deceleration theory were put forward respectively in this paper, and the friction resistance calculation models of the van body surface were established under the air film condition respectively.Thirdly, the friction resistance on the van body surface under the air film condition were researched by the CFD simulation in this paper. This paper explored the effects of different hole factors and velocity conditions on frictional resistance on the van body surface and air film parameters through simulation respectively. Different hole factors included the diameters of holes, the inclination of holes, the longitudinal spacing of holes, and the lateral spacing of holes. Different velocity conditions included different mainstream velocities and jet velocities. Then this paper obtained the optimum drag reduction effect of air film formation conditions.Finally, the simulate wind resistance tests study about the van models under the air film condition were conducted in this paper. A simplified and reduced scale van model was made, and the air film formation conditions was optimized. Comparison experiments verified the feasibility of application air film drag reduction on the van body surface.Another part of this paper is to reduce the negative pressure from the tail of van body through installation tail domes, three different lateral dimensions of tail domes including the 125 type, 500 type, 750 type were designed, and both the CFD simulation and wind resistance tests showed that the tail domes can realize drag reduction effectively. |
PDF Full Text Request