Effects of flow splitters on local scour downstream of type-A trapezoidal piano key weir

Abstract

This study investigates the effectiveness of flow splitters in reducing scour downstream of trapezoidal Piano Key Weirs through a comprehensive experimental study. Three distinct geometries of flow splitters—square, rectangular, and circular—are examined under various hydraulic conditions to assess their impact on local scouring. The experiments were conducted in a dedicated channel measuring 10 m in length, 0.75 m in width, and 0.80 m in height. The results indicate that flow splitters facilitate flow separation by linking trapped air beneath the flow to the free surface, thereby mitigating nappe oscillation. Additionally, the geometric variations of flow splitters did not significantly influence the upstream water head, with rectangular-shaped flow splitters proving more effective than square and circular splitters. On average, the maximum scour depth for the weir with rectangular, square, and circular splitters is reduced by approximately 13, 11, and 10%, respectively, compared to the weir without splitters. Furthermore, the volume of scour holes in tests with rectangular, square, and circular splitters showed reductions of 18.53, 17.77, and 14.92%, respectively, compared to tests without splitters. As discharge decreases, the effectiveness of these flow splitters in reducing scour depth becomes more pronounced. Due to the existence of splitters, the location of maximum scour depth approaches the weir. New equations were developed for predicting scour hole parameters with and without flow splitters, incorporating various splitter geometries. These equations were formulated using non-linear regression, achieving high accuracy with a correction factor, yielding R² values between 0.78 and 0.94, and RMSE values ranging from 0.09 to 0.54. Overall, the findings underscore the significance of flow splitter geometry in mitigating scour effects, providing valuable insights for future engineering applications.