Understanding the air injection strategy of a ventilated supercavity is important for designing high-speed underwater vehicles wherein an artificial gas pocket is created behind a flow separation device to reduce skin friction. Our study systematically investigates the effect of flow unsteadiness on the ventilation requirements to form ($C_{\mathit{Qf}}$) and collapse ($C_{\mathit{Qc}}$) a supercavity. Imposing flow unsteadiness on the incoming flow has shown an increment in higher $C_{\mathit{Qf}}$ at low free stream velocity and lower $C_{\mathit{Qf}}$ at high free stream velocity. High-speed imaging reveals distinctly different behaviors in the recirculation region for low and high freestream velocity under unsteady flows. At low free stream velocities, the recirculation region formed downstream of a cavitator shifted vertically with flow unsteadiness, resulting in lower bubble collision and coalescence probability, which is critical for the supercavity formation process. The recirculation region negligibly changed with flow unsteadiness at high free stream velocity and less ventilation is required to form a supercavity compared to that of the steady incoming flow. Such a difference is attributed to the increased transverse Reynolds stress that aids bubble collision in a confined space of the recirculation region. $C_{\mathit{Qc}}$ is found to heavily rely on the vertical component of the flow unsteadiness and the free stream velocity. Interfacial instability located upper rear of the supercavity develops noticeably with flow unsteadiness and additional bubbles formed by the distorted interface shed from the supercavity, resulting in an increased $C_{\mathit{Qc}}$. Further analysis on the quantification of such additional bubble leakage rate indicates that the development and amplitude of the interfacial instability accounts for the variation of $C_{\mathit{Qc}}$ under a wide range of flow unsteadiness. Our study provides some insights on the design of a ventilation strategy for supercavitating vehicles in practice.

了解通风超腔的空气注入策略对于设计高速水下航行器很重要，其中在流动分离装置后面创建人工气穴以减少皮肤摩擦。我们的研究系统地研究了流动不稳定对形成（$C_{\mathit{质量分数}}$) 和崩溃 ($C_{\mathit{质量控制}}$) 一个超腔。对流入流量施加的流量不稳定已显示出更高的增量$C_{\mathit{质量分数}}$ 在低自由流速度和更低 $C_{\mathit{质量分数}}$在高自由流速度下。高速成像揭示了在不稳定流动下低自由流速度和高自由流速度的再循环区域明显不同的行为。在低自由流速度下，空化器下游形成的再循环区域随着流动的不稳定而垂直移动，导致气泡碰撞和聚结的可能性较低，这对超空腔形成过程至关重要。再循环区域在高自由流速度下随着流动的不稳定变化可以忽略不计，与稳定的流入流相比，形成超腔所需的通风较少。这种差异归因于增加的横向雷诺应力，这有助于再循环区域的受限空间中的气泡碰撞。$C_{\mathit{质量控制}}$发现严重依赖于流动不稳定和自由流速度的垂直分量。位于超空腔后上部的界面不稳定性显着发展，流动不稳定和超空腔脱落的扭曲界面形成的额外气泡，导致增加$C_{\mathit{质量控制}}$. 对这种额外气泡泄漏率的量化分析表明，界面不稳定性的发展和幅度解释了$C_{\mathit{质量控制}}$在大范围的流动不稳定性下。我们的研究为实践中超空泡飞行器的通风策略设计提供了一些见解。