Surface Pressure Measurements to Characterize Bubbly Shock Properties on a Cavitating NACA0015 Hydrofoil

Cavitation partial cavity dynamics on a NACA0015 hydrofoil is shown to be multimodal. For given fixed inlet conditions, the cavity growth and shedding processes can lock into differing, multistep processes, resulting in varying shedding frequencies (Strouhal numbers). In the present study, time-resolved X-ray densitometry based void-fraction flow field measurements, high-speed cinematography, and surface pressure measurements are performed to examine such cavitation dynamics. X-ray visualization revealed the presence of both reentrant liquid flow and bubbly shock propagation, both of which can contribute to cavity pinch-off and shedding. The shedding dynamics on the examined hydrofoil is weakly multi-modal, compared to that observed on a hydrofoil with a smaller planform. Also, significantly faster bubbly shock propagation speeds were observed on the present model compared to the smaller model. By measuring surface pressure on the hydrofoil, it is shown that occurrence of cavitation at higher mean pressures requires stronger pressure rises across the shocks thereby increasing the shock speed.