Spectral Characteristics of Sheet/Cloud Cavitation

Abstract

Cavitation observations were made using a highly instrumented 2D NACA 0015 hydrofoil mounted in a specially designed water tunnel. It was found that the dynamic characteristics of the cavitation vary considerably with various combinations of angle of attack and cavitation number, σ. At higher angles of attack, two types of flow unsteadiness are observed. At low σ, a low frequency shedding of cloud cavitation results in a strong oscillation in lift and Δp at a Strouhal number, based on chord length, fc/U, of about 0.15. This frequency is relatively insensitive to changes in σ. As σ is raised, the harmonic content of the oscillations changes significantly. A spectral peak at much higher frequency is noted that increases in frequency almost linearly with cavitation number. Similar behavior is noted in the lift fluctuations. [S0098-2202(00)02503-7]