Air Movement Induced by Water Flow with a Hydraulic Jump in Changing Slope Pipes

This paper presents experimental and numerical results of air movement in sewer pipes. Both the airflow in a straight pipe and pipes with changing slopes were studied. The result from the straight-pipe model suggests that the air pressure gradient is built up in the pipe even when it is kept at atmospheric pressure at both ends. The combined effects of water drag and the pressure gradient were analyzed. A general method for estimating the airflow rate was proposed. Further, physical and numerical experiments were performed on air movement induced by water flow with a hydraulic jump in pipes with a changing slope. The ratios of air and water flow rates were found to be substantially higher than published values because of different air transportation mechanisms. The rough surface and air/water bubbly flow in the roller of the hydraulic jump can affect the momentum flux of the air phase, and this additional momentum needs to be incorporated in airflow modeling. (C) 2016 American Society of Civil Engineers.