Numerical evaluation of discharge coefficient and energy dissipation of flow over a stepped morning glory spillway

Abstract

A morning glory spillway usually has an ogee shaped crest and conveys spill water flow to its downstream vertical shaft followed by a horizontal tunnel. The ungated morning glory spillways should convey variable discharges, which nonlinearly depends on the reservoir water elevation. The variation of discharge for unit length of the crest may cause challenges on design of downstream crest curve (which affects coefficient of discharge and downstream crest negative pressure). Furthermore, formation of a horizontal vortex flow affects the spillway discharge. In this paper, in order to resolve these problems by energy dissipation and water flow aeration, variable size steps are mapped to downstream of the curved ogee crest of morning glory spillway. A finite volume base numerical flow solver is used to investigate the effects of the considered configurations on the hydraulic design parameters. In this work, having verified the pressure and aeration of the flow over an ordinary stepped spillway, the characteristics of flow over geometry of an ordinary morning glory spillway, as well as stepped spillway, are modelled and compared to the available measurements on laboratory hydraulic models. Finally, an existing ordinary morning glory spillway is computationally modelled by considering an alternative design of variable sized steps at downstream crest (by mapping their edges to the ordinary profile of the morning glory spillway). The stepped morning glory spillway alternatives are numerically simulated for various flow rates, and the computed discharge coefficients and energy dissipations are compared with simulation results for ordinary morning glory spillway of the case.

Discharge Coefficients of Standard Spillways at High Altitudes

“…Alkhamis et al, in 2021 [36], also used CFD numerical evaluation to predict the discharge coefficients over an ogee-shaped crest. In the same year, Haktanir and Khalaf [37] analyzed the discharge coefficients for radial-gated ogee spillways and concluded that the results in [4] are not sufficient to accurately estimate the discharge over an ogee spillway for the case of partially open gates.…”

Energy dissipation performance of the trapezoidal stepped spillway

“…The use of the Computational Fluid Dynamics (CFD) methods increases after the development of computer technology. Many researchers have analyzed the effect of different step geometries on energy dissipation rates numerically (Arjenaki et al, 2020;Ashoor and Riazi, 2019;Ghaderi et al, 2021Ghaderi et al, , 2020Hekmatzadeh et al, 2018;Li et al, 2020Li et al, , 2018Mohammad et al, 2016;Reeve et al, 2019;Shahheydari et al, 2015;Tabbara et al, 2005;Alkhamis et al 2021). In this study, trapezoidal stepped spillways (TSS), which have not been studied in the literature, were analyzed numerically with Flow3D software.…”