Jet Scour around Vertical Pile

Abstract

This study investigates the mechanism and the characteristic parameters affecting local scour around a vertical pile caused by turbulent circular wall jets. There are two basic scouring mechanisms: the pile obstruction and the jet diffusion mechanisms. The former is dominated by a horseshoe vortex system while the latter is controlled by the bed shear stress as the jet diffuses into the flow. Four types of equilibrium scour hole profiles were identified. The criteria for each type of profile are classified in terms of the densimetric Froude number Fo and the relative impingement distance X i /d o. Semiempirical equations were developed to delineate the boundary limits for the different profiles. The results show that the maximum equilibrium scour depth d se and the scour depth at the pile d pe are highly dependent on Fo ; and generally for large Fo , d se =d pe. The scour depths are insensitive to the relative size of the pile to jet diameter D /d o. However, X i /d o does not appear to affect d se /d o but it has a profound influence on d pe /d o.