Drag force investigation of cavities with different geometric configurations in supersonic flow

In order to prolong the residence time of the flow retaining in the supersonic flow, wall cavity has been widely applied in the scramjet combustor, and this affects the aerodynamic surface and imposes additional drag force on the hypersonic propulsion system. The two-dimensional coupled implicit Reynolds Averaged Navier-Stokes （RANS） equations and the RNG k？ε turbulent model were employed to investigate the flow fields of cavities with different geometric configurations, namely the classical rectangular, triangular and semi-circular, and the cavities with the fixed depth and length-to-depth ratio. At the same time, the drag force performances of the cavities were estimated and compared. The obtained results show that the numerical results are in very good agreement with the experimental data, and the different scales of grid make only a slight difference from the numerical results. The intensity of the trailing shock wave is much stronger than that of the leading one, and the area around the trailing edge of the cavities plays an important role in the chemical reaction in the scramjet combustor. With the fixed depth and length-to-depth ratio, the triangular cavity can strengthen the turbulent combustion in the scramjet combustor further, but impose the most additional drag force on the scramjet engine. The classical rectangular one can impose the least additional drag force on the engine, but the function of strengthening the combustion is the weakest. The influence of the semi-circular one is the moderate, but the machining process is more complex than the other two configurations.