Energy Dissipation and Air Entrainment in Stepped Storm Waterway: Experimental Study

2009

Exp Fluids

In high-velocity free-surface flows, air entrainment is common through the interface, and intense interactions take place between turbulent structures and entrained bubbles. Two-phase flow properties were measured herein in high-velocity open channel flows above a stepped chute. Detailed turbulence measurements were conducted in a large-size facility, and a comparative analysis was applied to test the validity of the Froude and Reynolds similarities. The results showed consistently that the Froude similitude was not satisfied using a 2:1 geometric scaling ratio. Lesser number of entrained bubbles and comparatively greater bubble sizes were observed at the smaller Reynolds numbers, as well as lower turbulence levels and larger turbulent length and time scales. The results implied that small-size models did underestimate the rate of energy dissipation and the aeration efficiency of prototype stepped spillways for similar flow conditions. Similarly a Reynolds similitude was tested. The results showed also some significant scale effects. However a number of self-similar relationships remained invariant under changes of scale and confirmed the analysis of Chanson and Carosi (Exp Fluids 42:385-401, 2007). The finding is significant because self-similarity may provide a picture general enough to be used to characterise the airwater flow field in large prototype channels. Cross-correlation time scale ( List of symbols

Section: Froude Similitudesupporting

confidence: 93%

Turbulence, dynamic similarity and scale effects in high-velocity free-surface flows above a stepped chute

2009

Exp Fluids

“…The surface was parallel to the pseudo-bottom formed by the step edges for θ = 26.6°. For the 8.9° slope, the free-surface was not completely parallel to the pseudo-bottom and some pseudo-undular free-surface profiles were observed as previously reported on a 3.4° stepped chute (Chanson and Toombes 2002a). The amount of entrained air appeared smaller for the stepped chute with θ = 8.9° possibly linked with the different cavity shape.…”

Section: Visual Observations Of Flow Patterns Flow Regimes and Flow supporting

confidence: 58%

Aeration, Flow Instabilities, and Residual Energy on Pooled Stepped Spillways of Embankment Dams

2013

J. Irrig. Drain Eng.

Air-water flow experiments were conducted on some flat and pooled stepped spillways with slopes of 8.9º and 26.6º in transition and skimming flows. The study comprised the observations of the flow patterns, some characteristic air-water flow properties and energy dissipation performances. The air-water flow properties showed some differences in terms of interfacial velocity, bubble count rate and turbulence intensity between the stepped chutes for the two channel slopes. These differences were also reflected in the residual energy data highlighting a better energy dissipation rate for the pooled stepped spillway with slope of 8.9º. However, the air-water flows on the pooled stepped spillways exhibited some instabilities and a safe operation must be tested in physical testing. The flat stepped spillway appeared the preferable design in terms of energy dissipation and flow stability.

“…The present results were qualitatively and quantitatively comparable to these earlier findings, although Chanson and Toombes (2002b) The flow resistance on stepped waterways was characterised by significant form losses caused by the steps. Following common practice (Rajaratnam 1990, Chanson et al 2002, the DarcyWeisbach friction factor was used to quantify the dimensionless boundary shear stress in stepped spillway flows.…”

supporting

confidence: 91%

Air–water flow measurements in a flat slope pooled stepped waterway

2013

Can. J. Civ. Eng.

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