Self-Aerated Hydraulic Jumps in Closed Circular Pipe: Intrusive Measurement of Internal Air–Water Flow Properties

A hydraulic jump taking place in a partially filled pipe is responsible for rapid change in the pipeflow dynamics and air content. The pipeflow self-aeration at hydraulic jump in a closed pipe has not been studied in terms of detailed air–water flow structures. In this work, a dual-tip conductivity phase-detection probe was used to intrusively measure the air–water flow of hydraulic jumps in a horizontal enclosed circular pipe with controlled air supply. The hydraulic jumps exhibited highly three-dimensional roller structures in the circular pipe. The distributions of void fraction, particle count rate, and longitudinal velocity were obtained in the vertical plane along pipe axis, and the characteristic quantities were compared to the literature data of open-channel hydraulic jumps in rectangular flumes. The intrusive measurement was challenged by the unstable hydraulic jump positions in the pipe due to the finite air ventilation condition, and the variations in repetitive sampling results were assessed. The air–water flow property distributions were overall comparable to those in quasi-two-dimensional hydraulic jumps, except for full-pipe downstream flows with roller interaction with the pipe ceiling. The secondary surface roller motions were found to be responsible for enhanced air–water mixing on the pipe centerline. The transverse nonuniformity of the bubbly flow structure and the impact of air vent dimension are to be characterized in future studies.