Thermodynamic Effects in Hydrofoil and Inducer Cavitation

The present paper illustrates the main results of an experimental campaign conducted in the Thermal Cavitation Tuimel and in the CPRTF (Cavitating Pump Rotordynamic Test Facility) at CentrospazdAlta S.p.A. Experiments have been carried out on a four-bladed axial inducer and a NACA 001 5 hydrofoil at various cavitation numbers, water temperatures, incidence angles (for the hydrofoil) and flow coefficients (for the inducer), in order to investigate the steadylunsteady characteristics of cavitation phenomena and their dependence on thermal effects. Measured cavity lengths, surface pressure coefficients and unsteady pressure spectra are in good agreement with the data available in the open literature and suggest the existence of a strong correlation between the behavior of cavitation and the induced flow instabilities in the two flow geometries. Thermal cavitation effects appreciably modify the nature, extent and geometry of the cavitation region but, rather surprisingly, do not seem to deeply affect the development of cavitation-induced flow instabilities. If confirmed, this finding would have significant implications in the scaling of these crucial phenomena in high-performance turbopumps.