Noise analysis of flow over an underwater cavity with gas entrapped inside

Flow-induced cavity oscillation is a major source of underwater noise, primarily caused by the shear-layer instability and a feedback mechanism at the cavity opening. In a practical underwater environment, the presence of entrapped gas in a cavity can significantly influence noise characteristics, yet its effects remain insufficiently understood. In this work, a gas–liquid underwater cavity is investigated concerning the shear layer oscillation and the associated pressure fluctuation characteristics due to the existence of gas. The gas–liquid cavity flow is simulated using large eddy simulation, and the gas–liquid interface is tracked by the volume of fluid method. The Ffowcs Williams–Hawkings equation was used for predicting the underwater radiated noise under different conditions. Results show that the presence of gas induces free-surface oscillations that resonate with the shear layer. Compared to the full water case, adding gas generally reduces overall noise levels at most flow velocities. Within a flow velocity range of 2–3 m/s, a strong resonance occurs, characterized by frequency locking at approximately 50 Hz and a sharp increase in sound pressure levels. These findings provide valuable insight into the flow and acoustic characteristics of an underwater gas–liquid two-phase cavity.