Abstract
The effect of sediment on the hydraulics of jet energy dissipation is an urgent issue for high dams built on sediment-laden rivers. Accordingly, flume experiments were conducted using a ski-jump type energy dissipator in flows of four sediment concentrations (0 kg/m3, 50 kg/m3, 150 kg/m3, and 250 kg/m3) to determine the effects on discharge, flow regime, and hydrodynamic pressure in a plunge pool. The results demonstrate that the effect of sediment on discharge is constant, regardless of sediment concentration, when compared to fresh water. The width of the nappe decreased with increasing concentrations of sediment. The length of the jet trajectory increased with upstream water head. The time-averaged pressure and fluctuation pressure both exhibited peaks, describing the impact of the jet on the bottom of the plunge pool. The maximum time-averaged pressure and maximum fluctuating pressure both noticeably increased with upstream water head and slightly increased with sediment concentration for a given flow condition. The results also demonstrated that the dominant frequency of fluctuation trends to lower values, and that both the fluctuating energy and vortex scale increase with increasing sediment concentrations due to increased viscosity. These findings can be used to improve energy dissipation in dams on sediment-laden rivers.
Highlights
The interest in energy dissipation in hydraulic structures has developed at an appropriate time, given the significant increase in the construction of large dams worldwide since the 1950s [1].The design of hydraulic energy dissipators for these dams is often a challenge, especially when dam parameters include high water head and large discharge [2]
The experiments flow rate ensures the dam in a hyperconcentrated sediment-laden river,in sothis the study were conducted to determine the relationship between flow rate and upstream water head effect of sediment on flow discharge is an important and urgent issue
This indicates that the higher the upstream water head, the more energy carried by the jet and applied to the slab, and the larger “hill” region following the peak of the root mean squares (RMS) indicates that the main stream impact region is larger
Summary
The interest in energy dissipation in hydraulic structures has developed at an appropriate time, given the significant increase in the construction of large dams worldwide since the 1950s [1]. Wang and Qian [37] performed experiments to study the turbulence structure of open channel flow and confirmed that the turbulence of a sediment-laden flow is less intense, with a smaller frequency and larger turbulence eddies in the longitudinal direction compared with clear water flow; the distribution of density probability and the autocorrelation coefficients of the fluctuating velocity were similar to that of a clear water flow. For a high dam in a hyperconcentrated, sediment-laden river, an impinging jet from a deep outlet and plunge pool are combined to act as an energy dissipator. Sci. 2018, 8, 1672heads (1.8 m, 1.85 m, 1.9 m) to study the effects of sediment concentration on 3 ofthe hydraulics of energy dissipation, as quantified by discharge, flow regime of nappes, and hydraulic pressure on the slab in the plunge pool.
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