Prediction of critical submergence for multiple intakes by superposition method

In this study, the critical submergence for multiple pipe intakes with no partition walls was investigated. In order to predict the critical submergence for an intake in a group of intakes, a ?superposition method? is proposed by basing on the potential flow solution. It is shown that the critical submergence for an intake in a group, can be predicted by superposing the imaginary sink surfaces (tangent to free surface) of all intakes when each one sited and works alone as a single intake in the oncoming flow with the same position and geometry as that they have in the group. The main general principle is as follows. ?In a group of intakes, the intake whose Rankine ovoid?s upper boundary matches the water surface above the intake, reaches the critical condition (air-entraining vortex just occurs) before others?. Experiments were conducted on a group of two or three intakes sited in a uniform canal flow. Experimental and theoretical results have indicated that in the case of multiple intakes, the critical submergence for an intake is larger than that in the case of a single intake sited and works alone in the oncoming flow with the same position and geometry as that it has in its group. The agreement between the theoretical and experimental results is found to be satisfactory. Key Words : Intake, vortex, air-entrainment, submergence