Direct numerical simulations were performed to investigate an active control strategy for supersonic (Mach 1.8 and 2.2) flows past a rectangle cavity with a length-to-depth ratio of 4. A steady mass injection is applied upstream of the cavity as the active control technique. The pressure oscillations are significantly suppressed by two mechanisms: (1) thickening and lifting of the cavity shear layer to alleviate downstream impingement with the cavity trailing edge and (2) weakening of the cavity shear layer instability. When the initial boundary layer thickness of the supersonic cavity flow is relatively small, a stronger mass injection leads to increased cavity shear layer thickening and uplift, increased weakening of the shear layer instability, and higher suppression of the pressure oscillations. When the Mach number equals 1.8, the dominant flow mode changes from the Rossiter II mode to the Rossiter III mode under active control, which is detected by the dynamic mode decomposition. However, the mode transition under active control substantially differs if the initial boundary layer thickness is relatively large, for which the pressure oscillation suppression controlled by the high-velocity upstream mass injection is not better than a low-velocity injection, owing to a higher shear layer instability. Mechanism (2) listed above is therefore more important than mechanism (1).

进行直接数值模拟以研究超音速（1.8 和 2.2 马赫）流过长深比为 4 的矩形腔的主动控制策略。在腔上游应用稳定的质量注入作为主动控制技术. 压力振荡通过两种机制得到显着抑制：（1）腔体剪切层的增厚和提升，以减轻与腔体后缘的下游冲击；（2）削弱腔体剪切层的不稳定性。当超音速空腔流的初始边界层厚度较小时，较强的质量注入导致空腔剪切层增厚和隆起增加，剪切层不稳定性减弱增强，压力振荡抑制能力增强。当马赫数等于 1.8 时，在主动控制下，主导流动模式从Rossiter II模式变为Rossiter III模式，通过动态模式分解检测到。然而，如果初始边界层厚度相对较大，则主动控制下的模式转变存在显着差异，由于较高的剪切，由高速上游质量注入控制的压力振荡抑制并不优于低速注入层不稳定。因此，上面列出的机制（2）比机制（1）更重要。由于较高的剪切层不稳定性，由高速上游质量注入控制的压力振荡抑制并不比低速注入好。因此，上面列出的机制（2）比机制（1）更重要。由于较高的剪切层不稳定性，由高速上游质量注入控制的压力振荡抑制并不比低速注入好。因此，上面列出的机制（2）比机制（1）更重要。