On the flow characteristics of two ventilated supercavities

This study presents an experimental and theoretical investigation into the interaction of two adjacent ventilated supercavities. Governed by the Froude number (Fr) and nondimensional lateral spacing (L/D_c), the two supercavities exhibit three distinct states: symmetric, asymmetric, and restricted symmetric. In the symmetric state, the two cavities are mirror images with respect to their central plane, whereas the asymmetric state arises due to small perturbations and is further amplified by the unstable equilibrium in the high-pressure region at the cavity tail. In the restricted symmetric state, the cavity tail is constrained by the support rod, resulting in a symmetric configuration within the observable range. In the symmetric state, as L/D_c increases, the maximum cavity radius near the symmetry plane initially increases and then gradually decreases. Conversely, in the restricted symmetric state, the maximum radius continuously increases with increasing L/D_c. The two ventilated supercavities exhibit four closure modes: Foam Cavity (FC), Reentrant Jet (RJ), hybrid Foam Cavity and Reentrant Jet (FCRJ), and Twin Vortex (TV). As L/D_c decreases, the occurrence of the FCRJ mode diminishes, while the TV mode becomes more prevalent. Compared to a single cavity, when one cavity operates in the FC or TV regime, the critical formation gas flow rate coefficient (C_Qf) of the adjacent cavity exhibits a slight increase or a significant decrease, respectively. Based on the potential flow theory, a differential equation was derived to describe the cavity shape near the symmetry plane, and its accuracy was validated through comparison with experimental data.