EXPERIMENTAL STUDY AND COMPUTATIONAL ANALYSIS OF PIANO KEY WEIR

Abstract

Piano Key Weir (PKW) is a further development of the well-known nonlinear labyrinth weir. Thus PKW is a similar type of labyrinth weir, which has a zig-zag shape in the plan, except that PKWs have a repeating rectangular profile. It replaces linear overflow structures by increasing the unit discharge at the same head and channel or spillway width. As a result, it is a viable option for newly constructed hydraulic systems and can significantly increase the evacuation and storage capacity of several existing hydraulic structures at a low cost. The hydraulic structures used as discharge measuring devices during flood release or open channel applications are free-to-flow spillways or weirs. PKW is a cost-effective solution for rehabilitation and new dam projects with a high level of constraints, for instance, limited space, small reservoir level, high specific flood discharge, etc. It has several advantages for preferring this structure instead of the labyrinth weir: it has less footprint area than other rectilinear labyrinth weirs, making it suitable for installation on top of existing or new gravity dams. It also has the inclined bottom of the keys instead of the horizontal-vertical arrangement of labyrinth weirs, improving their hydraulic efficiency. The main objective of this study is to examine the effect of the different geometrical parameters associated with PKW on its discharge carrying capacity by experimental and computational investigation. The study also deals with the various aspects of PKWs, including the energy dissipation, aeration performance, and other geometrical elements across the different types of the PKW. Moreover, soft computing techniques used the experimental data to generate the empirical equation to estimate the discharge capacity of the PKW correctly. A total of 60 laboratory-scale model configurations were examined and assessed to understand better the effects of PKW geometry on discharge efficiency, energy dissipation across the weir, and weir aeration performance. As a result, the impact of the following PKW geometries and modifications on discharge efficiency has been partially isolated: magnification ratio, inlet-to-outlet key slopes ratio, inlet-to-outlet key width ratio, upstream and downstream apex overhangs, and raising the crest elevation via a parapet wall. Based on the findings of this study, it was concluded that the discharge efficiency of the PKW increased or decreased with geometrical variations. Furthermore, the hydraulic performance of various types of PKW in terms of energy dissipation and aeration performance was investigated. It was concluded that Type-C dissipates more energy than type-A and type-B, but type-A has a higher aeration efficiency than type-B and type-C. However, type-B PKW has shown the most efficient PKW among the three.