Blade load dynamics in cavitating and two phase flows

Abstract

A comparative study of lift dynamics on a hydrofoil and inlet pressure dynamics on a pump impeller vane is described in this paper. The hydrofoil, a rectangular planform NACA 0015 with a chord length of c=0.081m, fitted with a special arrangement that allowed the injection of gas downstream of the minimum pressure point, was tested in the St Anthony Falls Laboratory (SAFL) closed loop water tunnel at the University of Minnesota. The SAFL water tunnel is specially suited for gas injection type measurements due to high gas removal capabilities. The tests on the hydrofoil also included a full range of cavitation experiments. The pump tests were made at the Waterpower Laboratory at the Norwegian University of Science and Technology (NTNU). Upstream of the pump inlet a special bubble injection device was located. This arrangement allows a controlled amount of gas to enter the flow. The water and gas flow rates were measured separately. Lift measurements from the hydrofoil study display a striking similarity between gas loaded and cavitation lift dynamics. The pump dynamics data show a maximum for a moderate gas void fraction. It is also observed that a more pronounced low frequency dynamics is present for the gas-loaded systems.