Experimental and Numerical Study on the Influence of the Incomplete Flaring Gate Pier Upon a Deep Tail Water Stilling Basin - Case study

Restricted by the insufficient energy dissipation inside a deep tail water stilling basin, the outgoing flow in low head projects often carries much excess energy to form a secondary hydraulic jump. Based on physical and numerical models, this paper creatively proposes an incomplete flaring gate pier to form anti-symmetrical water jets from adjacent chambers to improve the upstream situation. Detailed investigations are carried out to study the influence of incomplete flaring gate pier upon the downstream stilling basin. Results from both models show that there is almost no influence of incomplete flaring gate pier upon the discharge capacity of the overflow weir, especially for the condition of low water head difference. But significant influence can been noticed in the upstream region of the stilling basin. Due to the unique arrangement of flaring gate pier, a high-speed water jet and a submerged hydraulic jump can both exist at the entrance of the stilling basin, thus, forming great velocity gradients among adjacent inflows. Then, the high-speed water jet is forced to laterally offset, which results in a vertical vortex from the bottom to the surface. Compared to the traditional hydraulic jump, such compound flow pattern almost doubles the aeration concentration and involved depth in the upstream region of the stilling basin with the average velocity of outgoing flow being 25% down. The phenomenon of secondary hydraulic jump is eliminated.