Effect of the pipe bend of the morning glory spillway on the cavitation number

Abstract

Cavitation phenomena always threats the hydraulic structures with high velocity flow and suddenly varying the flow direction. It is assumed that the process of the flow depleting with high ratio through the morning glory spillway accompanied by suddenly varying the flow direction caused by the bend pipe can deteriorate the condition of the cavitation. Introducing the ratio R/D (diameter size of the vertical and horizontal shaft divided with radius of the bend pipe) can be beneficial to propose the novel design plan to avoid the cavitation caused by the bend pipe. Present study carried out a series experimental tests to validate a numerical model of the morning glory spillway with different R/D ratio to show the impacts of the suddenly varying the flow direction on the variation of the cavitation number. The cavitation values of the free, semi-submerged and submerged flow conditions showed that cavitation was mainly occurred on the internal arch of the bend pipe for free flow and the level of the danger for semi-submerged flow was the major danger level for internal arch of the bend pipe and due to submerged flow, the crest level at the entrance of the morning glory spillway was additionally threated by cavitation. To prevent from the cavitation, the values of the cavitation number due to different R/D as 0.55, 0.45, 0.35, and 0.25 were calculated by employing the validated numerical model due to high danger of the cavitation in semi-submerged condition. Results showed that due to D/R > 0.35, the possible cavitation damage is obtained for the internal and external arch of the bend pipe of the morning glory spillway; however, for D/R < 0.25, the bend pipe position is located in safe zone and the danger of the cavitation is negligible.