Air–Water Flow Patterns of Hydraulic Jumps on Uniform Beds Macroroughness

Abstract

Hydraulic jumps are characterized by strong flow turbulence, flow aeration, and three-dimensional flow motions. Whereas comprehensive research into hydraulic jumps on smooth bed has improved the understanding of flow aeration and turbulence, limited research has been done of hydraulic jumps on rough beds. Herein novel experiments were conducted in hydraulic jumps on uniformly-distributed bed macroroughness. Both air-water flow patterns and basic air-water flow properties were investigated. The hydraulic jumps on the rough bed exhibited some remarkable differences compared with smooth bed jumps including some preaeration of the flow upstream of the jump, an upwards shift of the jump roller and a clear water-flow region underneath the jump. Air-water flow measurements were conducted with a phase-detection probe, showing similar distributions of air-water flow properties for the rough and smooth bed jumps. Comparative analyses highlighted some distinctive effects of the bed roughness including an upwards shift of the hydraulic jump and an increase in bubble count rate and void fractions in the region close to the jump toe. In the second half of the hydraulic jumps, the rough bed led to a clear-water region with large-scale vortices which were advected downstream. The present study highlighted the potential that improved and nonstandard invert designs may have for flow manipulations and design enhancements.