Experimental analysis of shock smoothing design strategy for reducing cavitation erosion aggressiveness

Abstract

This article presents the experimental analysis of cavitation erosion for two cascade hydrofoil profiles. The aim is to evaluate the change in erosive intensity between a conventional smooth blade surface and one generated by the means of inverse design specifically to reduce cavitation aggressiveness. The applied design strategy consists in imposing a reduced amplitude and gradient at the cavity closure pressure jump in order to bring down the potential energy contained in the vapor sheet. The result is a unique geometry that presents a surface kink located at cavity closure, which successfully smoothes the pressure jump according to computational fluid dynamics (CFD) verification analysis. Here, an experimental rig is constructed and equipped with a pressure sensing system and high-speed imaging to capture the flow field. The measurements for both geometries are first compared against a set of steady-state CFD solutions, which demonstrate the reliability of the inverse design solver for generating targeted flow characteristics in non-cavitating and cavitating conditions. Visual recordings also reveal significant changes in the aspect of the vapor sheet between the two blades indicating a shift in its dynamic behavior. Erosion intensity levels are then measured by paint method at identical conditions. The outcome of the experiment is highly conclusive as a marked reduction in paint erosion is observed for the design geometry. The measured data also serve as a benchmark test for predictive cavitation erosion models by comparing the measured erosion distributions for each blade to those obtained numerically from unsteady CFD.