Prototype air–water flow measurements in D-type hydraulic jumps

Prototype hydraulic jump experiments were conducted at the Pei-bridge Gates in the Bao River, China. Two D-jumps formed on the 14° slope downstream one of the 5-m-wide sluice gates, followed by a sudden expansion of flow cross-section in the stilling basin. With the Froude numbers Fr = 7.47 and 3.18, the Reynolds numbers reached Re = 1.16 × 106 and 1.88 × 106, respectively. The fluctuating jump toe and free-surface characteristics were analysed and compared with existing model tests of classic and D-type jumps. The air–water flow properties were measured intrusively with phase-detection probes and compared to the laboratory data. The prototype jumps exhibited three-dimensional roller motions with shorter roller lengths than classic hydraulic jumps in prismatic channels. Scale effects were noted for the bubble frequency and bubble size distributions among the influences of other measuring factors, implying the need to revisit the model-based prediction relationship at prototype conditions.