Author(s): Paulo Povh; Jose Ota

Linked Author(s):

Keywords: Stepped spillway; Chamfer; Aeration; Energy dissipation; Skimming flow

Abstract: Hydraulics studies in physical models of stepped spillways developed by different researchers in the last decades were important to enable its use in hydraulic works. Most of experimental results of stepped spillways were obtained considering steps configured with sharp edge, however, some examples have shown that the practice can be a little different in prototypes. As a contribution, an experimental study was carried out using a 1:12 scale physical model of a stepped spillway considering steps edges with chamfers 4 cm side (prototype dimensions). A typical chute slope of 1V:0.75H and steps with nominal heights of 0.90 m and 1.80 m (prototype dimensions) were studied. Onset of aeration, depths, pressure and residual energy of the flow were registered. Formulations and analytical procedures proposed based on results obtained in chutes with conventional steps were used to compare to the results obtained with chamfered steps. The gradual aeration of the flow along the chute led to define a classification with different characteristics: from intermittent aeration of the steps to total aeration of the flow along the depth. Estimates from empirical formulations resulted close to the records classified by the continuous aeration of the steps. Depths calculated from an analytical method were close to those recorded in the non-aerated section along the central axis of the stepped chute. Flow profiles recorded along the side of the physical model enabled to compare the effect of using steps with nominal heights of 0.9 m and 1.8 m. Simulations carried out under the transition regime in the chute with 1.8 m high steps led to significant aerated depths. The residual energy was determined by calculating the supercritical conjugate depth of the hydraulic jump positioned at the base of the spillway. The dissipation of energy along the chute with 1.8 m high steps was slightly higher than that recorded with 0.9 m high steps. Instantaneous pressures along the axis and detailed mean pressure fields along the side of the stepped chute were measured. Low pressure values were recorded in the step chamfer region. The frequencies of occurrence of instantaneous pressures less than - 9 m.c.a. (prototype dimensions) in the chamfer region with the simulation of the specific flow of 34 m³/(s.m) resulted higher than 1,0 % in the chute with 1.8 m high steps.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022688

Year: 2022