| The flow-field structure and aerodynamic characteristics of pseudo shock significantly affect the aerodynamic performances of supersonic inlet diffuser and exit flow fields. Using the numerical simulation, this paper investigated the features of pseudo shock in supersonic inlet diffuser under different back pressures, different geometrical configurations and different free-stream parameters, and preliminary predications for aerodynamic performances of pseudo shock in supersonic inlet diffuser under real flow case were also carried out.Firstly, steady and unsteady simulations for the flow-field during the process of increasing back pressure are conducted to obtain the back pressure characteristics of the pseudo shock in the diffuser. Results show that: the interactive behaviors between shock/boundary layer interactions and the flow fields in the forepart of pseudo shock around the background shock reflection point could generate high-frequency oscillations, which will impact the matched control rules for the inlet and the whole engine. With the Mach number increasing, the length of pseudo shock get longer and the length and diffusing ratio affect the pseudo-shock characteristics by changing the shock trains length and the scale of separation. Based on a series of numerical results, a formula which can estimate the optimum diffusing ratio by the diffuser entrance Mach number and length has been proposed.Then, a series of diffuser is designed, and the corresponding flow-fields in the critical state are calculated. Through computational analysis, the influences of geometry parameters, including diffuser length, diffusing ratio and center line offset on the characteristics of pseudo shock wave in the diffuser section are gained. In the meantime, impacts of mass-averaged entrance Mach number are also analyzed. The results indicate that within the scope of the study, the performance of pseudo shock in diffuser is evidently affected by the diffuser length and diffusing ratio, while the influence of offset is slight. In the critical state,with the fowl Mach number increasing,shock trains which is the part of pseudo-shock get longer and the start position of pseudo shock move closer to the downstream. Based on a series of numerical results, a formula which can estimate the optimum diffusing ratio by the diffuser entrance Mach number and length has been proposed.Finally, the mass-averaged model and two level factor analysis method in DOE are used to initially predicts the aerodynamic performances of supersonic inlet diffuser under real free-stream conditions. Outcomes indicate that the mass-averaged model is not applicable to the predictions for performance parameters in supersonic inlet diffuser whose length is shorter than that of shock train. However, the two level factor analysis method of DOE is able to get fairly satisfying consequences, generally accommodating the accuracy requirements of fast evaluations in the engineering design area of supersonic inlet. |
