Theoretical analysis of transitional and partial cavity instabilities

This paper describes a new time marching calculation of blade surface cavit ation based on a linearized free streamline theory using a singularity meth od. In this calculation, closed cavity models for partial and super cavitie s are combined to stimulate the transitional cavity oscillation between par tial and super cavities. The results for an isolated hydrofoil located in a 2-D channel are presented. Although the re-entrant jet is not taken into a ccount, the transitional cavity oscillation with large amplitude, which is known to occur when the cavity length exceeds 75 percent of the chord lengt h, was simulated fairly well. The partial cavity, oscillation with relative ly high frequency was simulated as damping oscillations. The frequency of t he damping oscillation agrees with that of a stability analysis and of expe riments. The present calculation can be easily extended to simulate other c avity instabilities in pumps or cascades.