Abstract
Self-aerated flows in flat chutes are encountered downstream of the bottom outlet, in spillways with a small slope and in storm waterways. In the present study, the development of self-aeration in flat chute flow is described and new experiments are performed in a long flat chute with a pressure outlet for different flow discharge rates. The distribution of air concentration, time mean velocity and velocity fluctuation in flow direction in the self-aerated developing region—where air bubbles do not diffuse next to the channel bottom—were measured and analyzed. The region of self-aeration from free surface was about 27.16% to 51.85% of the water depth in the present study. The analysis results revealed that the maximum distance of air bubble diffusion to the channel bottom increased with the development of self-aeration along the flow direction. This indicates that for flat chute flow, the process of air bubble diffusion from free surface to channel bottom was relatively long. Cross-section velocities increased along the flow direction in the self-aerated developing region, and this trend was much more remarkable in the area near water free surface. The velocity fluctuations in flow direction in cross-sections flattened and increased with the development of self-aerated flow. Higher velocity fluctuations in flow direction corresponded to the presence of much stronger turbulence, which enhanced air bubble diffusion from the water free surface to channel bottom along the flow direction.
Highlights
Free surface self-aeration is frequently observed in steep rivers, spillways and flat chutes, such as tunnel spillways, partially filled pipes and high-speed flow in open channels connecting to a pressure outlet in bottom outlet tunnels
(i.e., the area of individual air bubbles in water). In this are obtained using a flat chute with a pressure outlet, and these characteristics of air–water paper, experimental abouttothe air concentration, time meanofvelocity and velocity flow aredata analyzed further understand the process self-aeration in high-velocity open fluctuation arechannel obtained using a flat chute with a pressure outlet, and these characteristics flow
The difference in velocity distribution at cross-sections indicated that for the self-aerated developing region in the flat chute flow, the velocity distribution deviated from the logarithmic law for the fully developed uniform flow
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Littledeveloping informationregion on theIIself-aerated developing region veloped uniform region are available to predict the air–water flow properties of superI in flat chute flows, especially about the diffusing process of air bubbles to the bottom critical flows [18,19,20]. Region I in flat chute flows, especially about the diffusing process of velocity air bubbles the fluctuation experimental data about the air concentration, time mean and to velocity bottom in developing region. I (i.e., the area of individual air bubbles in water) In this are obtained using a flat chute with a pressure outlet, and these characteristics of air–water paper, experimental abouttothe air concentration, time meanofvelocity and velocity flow aredata analyzed further understand the process self-aeration in high-velocity open fluctuation arechannel obtained using a flat chute with a pressure outlet, and these characteristics flow. The flume was 12 m long and 0.4 m wide with a
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