Scouring of sand beds by short impinging turbulent jets

Abstract

Laboratory experiments were carried out to study the scouring of sand beds by vertically impinging submerged circular turbulent water jets with short impinging height of 5.5 times the jet diameter. Measurements of the profiles of the static scour hole at different times were made along with the dynamic scour depths using a novel experimental arrangement. It was found that the asymptotic characteristic lengths of the scour hole can be predicted using the erosion parameter, Ec, of short impinging jet experiments. The ratio of the dynamic to static scour depths in asymptotic state varies between 2.1 and 4.3, for Ec ranges between 3 and 28. Semi-empirical prediction equations are developed for the asymptotic lengths and empirical equations are developed for the temporal development of the characteristic lengths. These equations show good correlations, with the coefficient of correlation (R2) varying beween 0.83 and 0.98. The shape of the dimensionless asymptotic scour hole is found to be different for short and long impinging jets. A general equation for its shape is developed considering the shape as a function of the submerged angle of repose of the bed material.