Experimental Investigation of an Instability on a Cavitating Propeller

Abstract

This paper presents results from experiments investigating an instability observed on a cavitating propeller. Preliminary visual observations were made of the attached cavities on the blades of the propeller, and particular note was made of similarities between the behavior of the re-entrant jets and that found recently by Laberteaux and Ceccio (1998). It was also noted that the nature of the instability is closely related to the partial cavity instability observed on single, two-dimensional foils. (Knapp, 1955; Wade and Acosta, 1966; Brennen, 1994, 95). The flow conditions (cavitation number and advance ratio) under which the instability occurs were mapped and it is shown that the onset corresponds to a specific configuration of attached cavity lengths on the propeller. Pressure measurements were obtained from two different locations within the experimental facility, and the acoustic signature of the instability is identified. A simple model based on cavity volume estimates obtained from high speed video footage is developed, and the predictions of the model are compared with the experimentally obtained pressures.