Visualization experimental study for venturi tube unsteady cavitating flows

Abstract

A visualization experiment of a venturi tube unsteady cavitating flows was conducted, by combining high speed visualization and dynamic pressure measurement technology, on the base of simulating the dynamical boundary conditions of the engine feed system. The detailed interior structure of cavitating flows and the pressure fluctuation data were captured. The variation of cavity shapes and the unsteady characteristics were analyzed. The experiment results indicate that as the cavitation number decreases, the venturi tube cavitating flow is changed from inception cavitation to film cavitation, and to cloud cavitation. At cloud cavitation stage, the venturi tube cavitating flows are revealed as some very complex dynamical processes. The cloud cavitating zone can be divided as attached annular cavity film and detached cavity cloud. The attached cavity film is relatively stable as a whole, and its inner pressure fluctuation is really little. It is found that large part of cavity cloud is breaking and shedding from the total detached cavity cloud, and is going to collapse. These processes induce evident pressure fluctuation pulses, which have wide frequency range but not fixable frequency peak in the frequency region. At the aft end of the cavity cloud, the local high velocity re-entrant flow is discovered, which drives the axial length of attached cavity film shortening and extending, and induces the film length obviously unequal along the circle. The self-oscillation of 290--400 Hz also takes place at the downstream system of venturi tube, at the cloud cavitation stage.