Author(s): Di Sun; Yun Liu; Ruidi Bai; Hang Wang
Linked Author(s): Hang Wang
Keywords: Partially-filled pipeflow; Pipe hydraulic jump; Free-surface measurement; Air-water flow measurement; Phase-detection probe
Abstract: When a hydraulic jump occurs in a drainage pipeline or flood discharge tunnel due to a local increase in flow resistance, it usually causes unfavorable flow conditions such as deterioration in discharge capacity, flow and air demand instability, and hydraulic vibration and noise. Compared to open-channel hydraulic jumps that have been extensively studied from basic flow pattern to detailed air-water flow structures, hydraulic jumps in enclosed circular pipes have received much less attention, not to mention the missing direct measurement of air entrainment in the transitional pipe flow. In this study, hydraulic jumps with free-surface rollers were generated in an enclosed horizontal circular pipe, with air fed into the partially filled pipe. Air-water flow properties, including the cross-sectional distributions of void fraction, bubble count rate and air-water interfacial velocity, were measured intrusively using a conductivity phase-detection probe on the flow centerline. The measurements were challenged by very unstable jump locations associated with the finite air supply. Similar to the open-channel hydraulic jumps, a turbulent shear flow region following the jump toe and a free-surface recirculation region above were observed, despite the strong three-dimensional structures formed by the circular pipe. The streamwise distributions of depth-averaged and cross-sectional maximum void fraction, maximum bubble count rate, and maximum air-water interfacial velocity all show a decreasing trend, comparable to the literature on classic hydraulic jumps in open channels. The free-surface fluctuations were preliminarily discussed based on intrusive wire gauge measurements.