Dual solution internal flow phenomenon and throttling characteristics of a supersonic variable inlet

A supersonic variable inlet with an operating Mach number ranging from 0–4 was designed to investigate its internal flow structures and throttling characteristics. All tests were conducted in the wind tunnel at a freestream Mach number of 2. 9 with the aid of the high-speed schlieren and dynamic pressure data-acquisition systems. The results show that when the Internal Contraction Ratio（ICR）is 1. 79，the unthrottled internal flowfield of the inlet has the dual solution of designed and undesigned flow states. In the designed flow state，the wave system in the inlet internal duct is normally established；while in the undesigned flow state，there is a complex wave system induced by local separa⁃ tion in the inlet internal contraction part，resulting in its overall pressure rise higher than that of the designed flow state and the presence of broadband，low-frequency small-amplitude oscillations. In addition，the inlet downstream throttling performance in the designed and undesigned flow states is comparable with critical throttling ratios of 42. 4% and 41. 7% and critical pressure ratios of 15. 8 and 16. 0，respectively. During the downstream throttling process in both types of flow states，the disturbance propagates upstream in the form of an oblique terminal shock train，and the head wave of the shock train in the critical state is located just near the throat station. However，apparent differences exist in the spatial distribution characteristics and oscillatory features of the terminal shock train of the two flow states. © 2023 AAAS Press of Chinese Society of Aeronautics and Astronautics. All rights reserved.