Hydrodynamics and Free-Flow Characteristics of Piano Key Weirs with Different Plan Shapes

This paper focuses on Piano Key Weirs (PKWs) as an effective solution for improving the discharge capacity of spillway systems. The flow behavior in inlet and outlet keys is experimentally studied to analyze the discharge capacity of PKWs with different plan shapes (i.e., rectangular, trapezoidal, and triangular). The results show that in outlet keys, the flow aeration regimes extend to higher values of headwater ratios (H-o/P) by increasing the length magnification ratio (B/w) and apex width ratio (A/w). In addition, the local submergence length is a decreasing function of A/w, especially in high flow heads. While the total interference length enlarges by reducing A/w in lower H-o/P values (H-o/P < 0.5), a reverse trend is observed in higher headwater ratios. PKW performance may also be impacted by the flow contraction and recirculation zone in inlet keys, which intensify in higher values of H-o/P, B/w, and A/w. According to the obtained results, while the discharge coefficient is a decreasing function of A/w in H-o/P > 0.4, it may have a reverse trend in lower head conditions. In addition, a trapezoidal PKW has the highest discharge efficiency in a wide range of the studied domain (H-o/P > 0.25 and B/w >= 2). It can improve the discharge efficiency by around 5%, while its body volume is almost 7% smaller than the traditional rectangular PKW. However, for low-length and high-head conditions (B/w = 1 and H-o/P > 0.5), the efficiency a rectangular PKW exceeds that of the other shapes.

Automated summary

This paper experimentally studied the flow behavior in Piano Key Weirs (PKWs) with different plan shapes and found that the local submergence length is a decreasing function of the apex width ratio, especially in high flow heads. A trapezoidal PKW has the highest discharge efficiency in a wide range, while a rectangular PKW may be more efficient in low-length and high-head conditions.