The influence of flow unsteadiness on erosive cavity dynamics

This paper presents investigations of unsteady flow conditions influence over cavitation dynamics. Measurements of wall pressure fluctuations in a model turbine are first introduced. It is shown that the wake of the spiral casing tongue modulates cavity dynamics near the trailing edge of runner blades. A new device, which permits a 2D hydrofoil to oscillate around its mean incidence angle, is used in order to recreate flow conditions similar to those of blade row wakes experienced in industrial flows. This device is mounted in the LMH High-Speed Cavitation Tunnel test section. Flow visualizations and surface pressure measurements are performed concurrently. Perturbations strongly affect leading edge cavitation at some flow conditions. Complete disappearance of leading edge cavitation can be imposed at a particular operating point. It is proposed that this behavior is associated with turbulent boundary layer transition. Pressure time signals obtained with the oscillating hydrofoil and the model turbine share common features that are different from those obtained with the hydrofoil set at fixed incidences.