Abstract
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 (Ho/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 Ho/P values (Ho/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 Ho/P, B/w, and A/w. According to the obtained results, while the discharge coefficient is a decreasing function of A/w in Ho/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 (Ho/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 Ho/P > 0.5), the efficiency a rectangular PKW exceeds that of the other shapes.
Highlights
Spillways play an essential role in the safety and service of water reservoirs; they are designed to safely pass floods, especially after considering the growing climate change effects leading to more extreme flood events [1]
To gain new insights into Piano Key Weirs (PKWs) flow physics through studying water surface profiles and velocity fields in inlet keys and nappe aeration and interference in outlet keys; to estimate the discharge capacity of PKWs with different plan shapes and analyze their performance based on the findings and observations of the complex flow structure
This paper studies the flow behavior around PKWs with different plan shapes in the This paper studiesofthe flow behavior ofaround with differentconclusions: plan shapes in wide ranges
Summary
Spillways play an essential role in the safety and service of water reservoirs; they are designed to safely pass floods, especially after considering the growing climate change effects leading to more extreme flood events [1]. A survey of US Army Corps of Engineers indicates that ~30% of existing dams are currently unsafe due to having inadequate spillway capacity [2]. A nonlinear weir with a folded crest in plan view improves the discharge capacity of spillway systems by extending the crest length for a given channel width. It can be an economical and effective solution for those sites where the structure width is limited while a large discharge capacity is required [5]. Bi = inlet allow for the implementation of PKWs in challenging situations such as the top of concrete overhang length, A = inlet key (or downstream) apex width, D = outlet key (or upstream) dams or steep, narrow streams.
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