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Numerical investigation of the unsteady behaviors of the hypersonic inlet caused by throttling was carried out by means of large- eddy simulation for a free stream Mach number 5.9 and the unit Reynolds number approximately 5.2 × 106 m -1 . Results have been validated carefully against experimental data. The throttling was caused by the plug placed near the exit of isolator. Two typical cases with and without plug are investigated. Various fundamental mechanisms dictating the flow phenomena inside the isolator have been studied systematically. The results of this study provide physical insight into the flow behaviors caused by the throttling.

Numerical investigation of underexpanded sonic coaxial jets was carried out using large-eddy simulation. The system consists of two coaxial nozzles, in which one is inner round nozzle and another is outer annular nozzle. Since the pressure ratio of inner to outer nozzle dominates the flow structures and behaviors, two typical pressure ratios 5/3 (case A) and 3/5 (case B) are considered. The calculated results have been validated carefully against experimental data. Based on the analysis of the flow structures, different shock systems and vortex shedding processes for the two cases are identified and some main flow characteristics of sonic coaxial jets are found. The power spectral analysis of pressure evolution is performed to demonstrate the frequency characters in the flow field. The mixing behaviors determined by different approaches are also discussed. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the underexpanded sonic coaxial jets interaction.