Air Demand of a Hydraulic Jump in a Closed Conduit

Abstract

Understanding the air demand of a hydraulic jump in a closed conduit is important in hydropower operations and urban sewer designs. In this study, physical experiments are described to study flow regimes and the air demand of a hydraulic jump in a closed conduit with various submerged outlet depths. Flow regimes with a submerged outlet were defined following previous studies based on outlet depth. Free-surface supercritical flow with a hydraulic jump can induce a relative air demand (air flow rate to water flow rate) of approximately 3%–14%. If the hydraulic jump is followed by pressurized pipe flow, the air demand decreases with increasing outlet depth until the return roller is fully developed in the pipe. For the partially submerged hydraulic jump, the relative air demand is significantly reduced to less than 1%. Field measurements of the air demand at the Hugh Keenleyside Dam, British Columbia, were consistent with the experimental measurements for the partially submerged hydraulic jump. The dynamics of the air pocket upstream of the hydraulic jump was studied. If the air supply was constrained by nozzles of various sizes placed on the top of the air vent, the air pressure in the closed conduit decreased and the hydraulic jump was pushed upstream. The energy loss coefficient in the air vent was also studied.