Vehicles Drag Reduction With Control of Critical Reynolds Number

Abstract

Various vehicles have been designed as short blunt bodies. Drag coefficients of these bodies are high because adverse pressure gradients cause boundary layer separation from their surfaces, but a reduction of the size of separation zone allows for a substantial reduction of the body drag. It can be done via displacement of their boundary layer separation far downstream. In this study, such displacement was achieved with a combination of passive and active flow control. First, the whole body side surface includes two constant pressure surfaces of selected lengths and the surface of a high adverse pressure gradient in the middle of them. Second, the boundary layer suction maintained on this middle surface prevents separation there. The concept feasibility is manifested for very short axisymmetric bodies (of length to width ratios from 1.02 till 1.25). For moderate Reynolds numbers (from 3,000,000 to 10,000,000) and at the optimum suction intensity, the total drag coefficient of the designed bodies is about tenfold lower than the drag of spheroids of the same slenderness. The 3D design problem is also considered.