The Influence of Pressure Gradient on Desinent Cavitation From Isolated Surface Protrusions

Abstract

An experimental investigation was conducted to study the desinent cavitation characteristics of various sizes of two-dimensional triangular and circular arc protrusions in a turbulent boundary layer for favorable, zero, and unfavorable pressure gradients. The roughness height (h ) varied from 0.025 cm (0.01 in.) to 0.762 cm (0.30 in.) and the relative height (h /δ) varied from 0.026 to 2.53. Desinent cavitation numbers (σd ) were obtained visually over a velocity range of 9.1 mps (30 fps) to 18.3 mps (60 fps) at an average total air content of 3.8 ppm (mole basis). The data for zero pressure gradient were in fair agreement with data obtained for the same protrusion shapes by Holl (1958). The cavitation number (σd ) was correlated with relative height (h /δ), Reynolds number (U δ/ν) and Clauser’s (1954) equilibrium boundary layer shape factor (G ) which includes the effect of pressure gradient. The data show that σd increases with pressure gradient. This result was not expected since it appears to contradict the trends implied by the so-called characteristic velocity theory developed by Holl (1958).