Effect of apron roughness on flow characteristics and scour depth under submerged wall jets.

Scour downstream of smooth and rough rigid aprons under wall jets has been studied experimentally. Effect of apron roughness on scour has been investigated, and quantification of reduction in the scour depth due to rough apron has been performed. Characteristics of velocity and turbulence over smooth and rough aprons as well as within the scour hole have been analyzed to study the behavior of the jet and its interaction with the rough apron. Results show that there is a significant reduction in the equilibrium scour depth due to roughness. A maximum of 82.8% and a minimum of 31.1% reduction in the equilibrium scour depth was observed due to inducing roughness over the rigid apron. Velocity characteristics establish the cause of reduction in the equilibrium scour depth, which is due to reduction in the erosive capacity of the jet as it moves over the rough apron. The potential core of the jet gets consumed at a much lesser length due to roughness over the apron than over a smooth apron, as the boundary layer develops at a smaller distance. Further, it was observed that it takes a smaller length for the flow to get fully developed under the rough apron as compared with the smooth apron. Based on the results of the present analysis, recommendation can be made for use of roughness over the apron to restrict scour due to wall jets. [ABSTRACT FROM AUTHOR]