Energy Dissipation of Type a Piano Key Weirs

Abstract

A Piano Key weir (PK weir) is a nonlinear, labyrinth-type weir well suited for rehabilitation projects due to a relatively small footprint and the ability to pass large discharges for lesser upstream-head values when compared with other weir types. A critical component of a hydraulic structure is the energy-dissipative properties. Currently, information and guidance is limited, with previous energy dissipation studies of PK weirs primarily of specific projects. Therefore, to document and quantify energy dissipation, four laboratory-scale Type A PK weir models with different width ratios (Wi/Wo) were studied, with 255 tests comprising this new dataset, along with detailed observations of the flow field. Results were compared to existing published data regarding energy dissipation downstream of trapezoidal and rectangular labyrinth weirs. To support design efforts, two equations, both functions of head-water ratio (H/P) and Wi/Wo, are proposed to predict the relative residual energy downstream of PK weirs. The energy dissipation of PK weirs is largest at low flows and decreases in a logarithmic-like manner as flow increases. PK weirs with increased hydraulic efficiency, caused by an increase in Wi/Wo, resulted in slightly smaller energy dissipation values within the range 0.2 ≤ H/P ≤ 0.8. The energy dissipation of PK weirs was found to be relatively constant, independent of Wi/Wo, and in the ranges 0.07 ≤ H/P ≤ 0.2 and 0.8 ≤ H/P ≤ 0.95.

Evolution of local scour downstream of Type A PK weir in non-cohesive sediments

“…Corresponding hydraulic conditions were calculated to be: hc = 0.20 m, hd = 0.43 m with g = 9.81 m/s 2 . ΔH = 0.25 m can be estimated using a head-discharge rating curve with corresponding H and energy dissipation from Eslinger and Crookston (2020). As discussed herein, the majority of scour would be expected to occur in Phase 1, thus for sufficiently long durations of flow, a maximum scour depth can conservatively be assumed.…”

Sediment Movement over Type A Piano Key Weirs

“…Hence, the main governing factor behind such observations is the slopping inlet key. The downstream scouring has been studied by Jüstrich et al (2016); Kumar and Ahmad (2020), and it is directly affected by the residual energy which has been studied by Eslinger and Crookston (2020); Silvestri et al (2013). CFD simulation has also been used by several researchers to study different aspects related to PKW.…”

Study on aeration performance of different types of piano key weir

“…On the other hand, the air circulation region grew substantially with H t , partly because the regional speed increased, resulting in higher advection levels and turbulent mixing. This flow behavior increases the aeration efficiency of the PKW because the complex flow nature creates more air bubbles for a greater time and longer path (Eslinger & Crookston 2020).…”