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Experimental Investigations of Cavitation Breakdown in an Axial Waterjet Pump

Excerpt

This paper provides detailed experimental data on the changes to the flow structure and cavitation occurring in an axial waterjet pump as the pressure is reduced causing cavitation breakdown. The database includes performance curves, high-speed images of the cavitation and velocity distributions inside the blade passage obtained using Stereo-PIV (SPIV). The corresponding pressure distribution is estimated using Bernoulli’s Equation and the changes to the velocity from the inlet to the interior of the passage. Results show that cavitation breakdown is initiated by the rapid expansion of the attached cavitation on the blade suction side (SS) into the blade overlap region, blocking part of the entrance to the passage, and increasing the velocity along the pressure side (PS) of the blade. The resulting reduction in PS pressure along with the vapor pressure in the attached SS cavitation reduces the blade loading. Furthermore, entrainment of the cloud cavitation by the tip leakage vortex (TLV) also generates large scale cavitating vortical structures, which are aligned perpendicularly to the SS surface, and extend to the next blade. They reduce the throughflow in the tip region. The combined effects of reduced blade loading and tip blockage contribute to the cavitation breakdown.

Introduction
Experimental Setup
Cavitation Performance
Appearance of Cavitation
Velocity and Pressure Distributions
Discussion and Conclusions
References
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