Flow Instabilities on a Three-Bladed Axial Inducer at Variable Tip Clearance

The paper illustrates the results of an experimental campaign conducted at Alta S.p.A. in the CPRTF (Cavitating Pump Ro-tordynamic Test Facility). Tests have been carried out at two val-ues of the blade tip clearance on the three-bladed DAPAMITO-3 inducer, designed and manufactured by Alta S.p.A. with geometry and noncavitating performance representative of typical space rocket inducers. Different cavitating behavior has been observed at different values of the blade tip clearance, particularly near breakdown conditions. The intensity of pressure oscillations tends to decrease as the tip blade clearance increases, and cavitation-induced azimuthal flow instabilities appear to be more sensitive to changes of the blade tip clearance than axial flow instabilities. Finally, the presence of backflow seems to have a stabilizing effect on rotating cavitation instabilities.