Investigation of pressure distribution characteristics of two cavities under gust flows

The flow characteristics of two parallel cavities under unsteady flow conditions are essential for the cooperative control of high-speed underwater vehicles. In this study, a validated unsteady RANS-VOF numerical method combined with a multi-peak Gaussian fitting algorithm is adopted to quantitatively investigate the temporal evolution of internal pressure distribution within two ventilated supercavities under periodic gust disturbances. The results indicate that gravity induces a nearly twofold difference in the geometric size of the two cavities. The pressure histogram of the larger cavity presents prominent multi-peak characteristics, and vortex structures are identified as the dominant factor governing the formation of such peak features. Furthermore, the pressure subpeaks experience splitting, shifting and merging behaviors, resulting in three typical pressure distribution patterns: stacking, erosion and nesting. The Bhattacharyya coefficient is subsequently introduced to quantify the pressure deviation from the steady-state condition, which reflects the coupled effects of cavity deformation and closure-phase fluctuation. Increasing gust amplitude and frequency triggers progressive cavity deformation, vortex shedding and even local collapse, thereby fundamentally altering the internal pressure distribution. Additionally, the cavity closure phase imposes a periodic modulation on the pressure field. For the upper cavity, such modulation corresponds to the transition between re-entrant jet (RJ) and twin-vortex (TV) closure modes, while for the lower cavity, it dominates the size fluctuation of twin-vortex tubes. Notably, within the range of gust amplitude A_g<0.75 m/s and frequency 1 Hz<f_g<15 Hz, the sinusoidal oscillation of the closure phase excites a natural frequency in the distribution of the Bhattacharyya coefficient. Specifically, the natural frequency of the upper cavity varies linearly with the gust frequency, whereas the lower cavity maintains a constant natural frequency of 2π.