The effect of the block on the tunnel structure in the outlet keys of the piano key weir on its downstream local scour

Document Type : Research Article

Authors

1 Department of Civil Engineering, Isf.C., Islamic Azad University, Isfahan, Iran

2 Department of Civil Engineering, Faculty of Engineering, University of Karbala, Karbala, Iraq

10.22060/ceej.2026.24423.8305

Abstract

Piano key weirs are a new type of non-linear labyrinth weirs. Due to the high efficiency of these weirs in flow passage, it is of great importance to investigate local scour and the solution to reduce it. In the present study, different block geometries were used in the tunneled outlet keys of the rectangular piano key weir type B. The piano key weir used is 0.20 m high and has three cycles (three outlet keys, two inlet keys, and two inlet half keys). Rectangular, trapezoidal, and cylindrical block geometries were installed in each outlet key of the weir and on the tunnel structure. The tunnel structure prevented the flow exiting from the inlet and outlet keys from mixing. The blocks direct the flow and the maximum scour depth to a distance further from the weir toe, acting as a barrier to the flow and reducing the velocity of the flow exiting from the keys. A further distance of the maximum scour depth from the weir toe can reduce the risk of the weir overturning. In rectangular blocks, the maximum scour depth decreases, and its location is further from the weir toe. Also, as the densimetric Froude number increases, the flow rate rises and the tailwater decreases; the maximum scour depth also increases. The range of the densimetric Froude number in the present study varies between 0.43 and 0.55. Finally, dimensional analysis was used to generalize the results to nature and other models of piano key weirs.

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Amirkabir Journal of Civil Engineering
Volume 57, Issue 12
in progress
March 2026

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