Abstract: The unsteady flow characteristics of hypersonic inlet and the influence of the internal compression duct geometry on them during self-starting were studied with the unsteady numerical simulation. The results show that: the unsteady flow characteristics are influenced by the internal compression duct geometry and the free-stream condition. The curvature radius of the shoulder of internal compression surface is larger, the contraction rate of internal compression duct is slower, and the flow oscillation occurs easily with stronger oscillation intension. But, the flow oscillation disappears when the curvature radius of the shoulder is small enough ( the geometry parameter β≯33°). If the flow oscillation occurs during inlet self-starting, the oscillation frequency decreases and the no oscillation、oscillation、no oscillation and started mode appears one by one with the increase of free-stream Mach number . And for the case that the flow oscillation does not occur during self-starting, the inlet suffers the hard-unstarted mode 、soft-unstarted mode and started mode in sequence with the free-stream Mach number increasing.

Key words: self-starting, unsteady, flow oscillation, hypersonic inlet, numerical simulation