Cavitation and Flow Instabilities in a 4-Bladed Axial Inducer Designed by Means of a Reduced Order Analytical Model

Abstract

The paper illustrates the results of an experimental campaign conducted at Alta S.p.A. in the CPRTF (Cavitating Pump Rotordynamic Test Facility). Tests have been carried out in water on the four-bladed DAPAMITO4 inducer, designed and manufactured by means of a reduced-order model developed at Alta S.p.A., at several values of the flow coefficient and the water temperature. Several non-synchronous instabilities have been observed on the inducer, including an axial surge, a backflow oscillation and, at higher temperatures, an incipient rotating cavitation and a backflow vortices instability. In addition, a synchronous rotating cavitation (also leading to the characteristic “one step” shape of the cavitating performance curve near to head breakdown conditions) has been detected at all the investigated flow conditions, and the amplitude of oscillations associated to this instability generally tends to decrease at higher water temperatures. Nomenclature % A amplitude of oscillations (expressed as % of the maximum value) % c tip clearance/mean blade height ratio n number of lobes in p inlet static pressure [Pa] V p vapor pressure [Pa] Q volumetric flow rate [m 3 /s] T r inducer tip radius [m] T water temperature [°C] α incidence angle b β blade angle evaluated w.r.t. the azimuthal direction [rad] γ xy coherence function Δp static pressure rise across the inducer [Pa] t p Δ total pressure rise [Pa] θ