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.
By using our computational fluid dynamic models, a new type of single engine capable of operating over a wide range of Mach numbers from subsonic to hypersonic regimes is proposed for airplanes, whereas traditional piston engines, turbojet engines, and scram engines work only under a narrower range of operating conditions. The new engine has no compressors or turbines such as those used in conventional turbojet engines. An important point is its system of super multijets that collide to compress gas for the transonic regime. Computational fluid dynamics is applied to clarify the potential of this engine. The peak pressure at the combustion center is over 2.5 MPa, while that just before ignition is over 1.0 MPa. The maximum power of this engine will be sufficient for actual use. Under the conditions of higher Mach numbers, the main intake passage located in front of the super multijet nozzles, takes in air more. That results in a ram or scramjet engine for supersonic and hypersonic conditions.
