Blocks on the tunnel structure and their effect on flow energy dissipation in a type B rectangular piano key weir (PKW)

Document Type : Original Research

Authors
Wadi Mohammed Wadi 1
Ali Khoshfetrat 2
Musa Habib Jasim 3
Niloofar Salemi 1
1 Department of Civil Engineering, Isf.C., Islamic Azad University, Isfahan, Iran
2 Assistant Professor, Water Studies Research Center, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
3 Department of Civil Engineering, Faculty of Engineering, University of Karbala, Karbala, Iraq
10.48311/mcej.2025.116626.1004
Abstract
Piano key weirs (PKWs), as an evolved type of non-linear labyrinth weir, are notable for their high discharge efficiency. This research primarily aims to investigate the rate of energy dissipation and strategies to enhance it by using blocks of different geometric shapes installed on a type B rectangular PKW outlet key. The experiments were conducted in a flume 10 m long, 0.8 m wide, and 1 m high. The weir was installed 5.5 m from the channel's inlet. Three different weir heights (0.20, 0.18, and 0.15 m) and three block shapes (rectangular, circular, and trapezoidal) were studied. The findings indicate that the highest energy dissipation is associated with rectangular, trapezoidal, and circular blocks, respectively. Increasing the weir height by factors of 1.11 and 1.33 compared to the minimum height resulted in energy dissipation increases of 6.8% and 18.8%, respectively. Furthermore, as the weir height increases, the discharge coefficient decreases. A comparison of the results showed that the presence of a tunnel structure leads to significantly higher energy dissipation compared to the case without it. Finally, dimensional analysis was used to calculate energy dissipation for weirs with and without blocks, allowing the results to be generalized to prototype conditions and other types of PKWs.
Keywords
Piano key weir
Weir height
Relative energy
Outlet keys
Type B
Subjects
Modares Civil Engineering Journal
Volume 26, Issue 5 - Serial Number 91
November and December 2026
Pages 21-33