采用非定常数值仿真的方法研究了低于自起动马赫数时高超声速进气道的非定常流动特性.研究表明:低于进气道自起动马赫数时,进气道处于不起动状态,流场发生喉道壅塞性振荡现象,其流场振荡频率为250Hz.流场振荡主要发生在喉道之前,对其后流场影响相对较小,扰动信号由喉道以当地气流速度向下游传播.隔离段长度对喉道壅塞性流场振荡几乎没有影响.飞行马赫数较小时流场未出现振荡现象,当飞行马赫数靠近自起动马赫数时流场出现周期性振荡现象,并且随着飞行马赫数的增大,此类流场振荡趋于强烈;进气道压差阻力随着时间推进呈现周期性变化,振荡频率同样为250Hz. Unsteady numerical simulation is used to study the unsteady flow behavior of a hypersonic inlet below a self-starting Mach number. The results show that the inlet is in a non-actuated state below the self-starting Mach number of the inlet, And the oscillation frequency of flow field is 250 Hz.The flow field oscillation mainly occurs in front of the throat, which has a relatively small influence on the flow field afterwards, and the disturbance signal propagates downstream from the throat at the local airflow velocity. The length of the isolation section has almost no effect on the thunderstorm flow field oscillations.When the flight Mach number is small, there is no oscillation phenomenon in the flow field, and when the flight Mach number approaches the self-starting Mach number, periodic oscillations appear in the flow field, The increase of the number of such flow field oscillation tends to be strong; drag resistance of the inlet presents cyclical changes over time, the same oscillation frequency of 250Hz.