Experimental and Numerical Studies of the Influence of Zigzag Crests with Various Geometries on the Flow Field and Scour Downstream of Rectangular Piano Key Weirs

Abstract

Abstract In this research, the flow and scour patterns downstream of a rectangular Piano Key Weir (PKW) were studied experimentally and simulated by using the Flow-3D numerical model and with RNG turbulence model. It was found that the Flow-3D model simulates the scour downstream of a PKW with acceptable accuracy. Variations of the bed topographical downstream of type-A PKWs with different crest shape (i.e. standard crest and with zigzag indentations in various geometries, including: triangulate, half circular, sinusoidal, rectangular and fort crest) were investigated. The results demonstrate that the zigzag indentations of the lateral crest walls substantially influenced the geometrical characteristics of the scour hole including: scour depth at the weir toe, maximum scour depth, scour hole area and scour hole volume. The lowest value of maximum scour depth was occurred downstream of the PKW with the triangulation indentations, in this case a decrease of 10.5 and 17% in the longitudinal and vertical components of flow velocities, at the weir crest level and below the crest level, led to a reduction of 38% in the local scour, respectively. The higher energy of flow in the weir with the rectangular indentations caused the maximum scour depth location to occur at a farther distance from the weir toe. Also, the lowest upstream and downstream slopes of the scour hole were observed in the two weir models with rectangular and fort crest shapes.