Inhibition of cloud cavitation with actively controlled flexible surface driven by piezoelectric actuator

Cloud cavitation in hydraulic machines can lead to severe vibration, noise, and surface damage, ultimately degrading performance. To address this issue, this study investigates the mitigation effects of an actively controlled flexible surface on typical cloud cavitating flow over a hydrofoil. A two-way fluid-structure interaction computational model is developed by coupling the unsteady Reynolds-averaged Navier–Stokes equations with structural dynamic equations. Flexible surfaces driven by piezoelectric actuators with different actuation frequencies and amplitudes are strategically arranged at three representative regions along the hydrofoil. Results demonstrate that high-frequency and high-amplitude actuation effectively mitigates cloud cavitation phenomena. Notably, large-scale cavity shedding from the upstream region transitions into small-scale cavity shedding in the closure region. The presence of flexible surfaces enhances the thickness of the re-entrant jet while reducing its velocity, thereby diminishing its ability to pinch off the cavity. Fourier analysis reveals that fluctuations in vapor fraction at the actuation frequency predominate in the shear layer, propagating from the leading edge of the cavity to its wake. Furthermore, a one-dimensional model indicates that pressure fluctuations throughout the domain arise from the volume changes induced by the flexible surface, positively correlating with the second time derivative of the resultant volume. Consequently, it is concluded that flexible surfaces actuated by piezoelectric patches serve as an effective method for mitigating cloud cavitation.