Investigation of unsteady cavitation dynamics over a hydrofoil subject to controlled pitching motion

We present a numerical study to examine the influence of low-amplitude controlled pitching motion on the unsteady turbulent cavitating flow over a NACA66 hydrofoil section at Re= 800000. We simulate multiphase flow dynamics in an Arbitrary Lagrangian-Eulerian coordinate, utilizing a highly validated variational finite element approach and homogeneous mixture-based cavitation model with a hybrid URANS-LES approach for turbulence effects. To decouple the cavitation shedding dynamics from trailing edge vortex dynamics, we employ prescribed sinusoidal pitching motion to the hydrofoil at select harmonics of the cavitation shedding frequency. The cavity growth and detachment are forced to delay, limiting the cavity to a thin attached harmonic oscillating layer driven by the pitching frequency for majority of its life, while minimizing cloud shedding. Additionally, increased negative vorticity over the suction surface by pitching motion is adjusted to balance the trailing edge vortex, enforcing a reorganization of the turbulent wake. This targeted decoupling control strategy achieves a significant reduction in the drag forces over the hydrofoil, with slight increase in the lift. The observations are seen to be consistent over a range of cavitation numbers above super-cavitating regime.