Influence of Wall-Attached Vortices on the Pump Installed in the Suction Pipe of an Open Intake

Abstract

Wall-attached vortices in pump intake commonly appear and damage the stability of the whole pump station. Revealing the effects of these vortices on the pump performance is crucial for safe operation. In this paper, scale-adaptive simulation based on the shear stress transport k-ω model was performed on a pump intake with an axial-flow pump installed in the suction pipe. Three submergences (3.0, 4.0, and 4.67 DL, where DL is the bell mouth diameter) and three flow rates (0.8, 1.0, and 1.2 Qd, where Qd is the design flow rate) were studied. It was demonstrated that the intake vortex structures were significantly different in the cases with and without the pump being installed. Under different conditions, the backwall vortices appeared first, then floor vortices and the sidewall vortices appeared at last. It was found that only backwall vortices entered the impeller. The strength of the vortices increased as the flow rate increased. The fluctuation of head and efficiency was related to the nonaxial inflow at impeller inlet. In order to evaluate the influence of backwall vortices, the entropy loss coefficient based on entropy theory was defined. It was found that, although flow separation occurred on the blades, the main source of entropy production was backwall vortices. The open intake is important for affording desired flow condition to the pump to ensure the safe and stable operation of the pump station. While the wall-attached vortices, including floor, backwall, and sidewall vortices, are usually inevitable, it is known that these vortices can affect the pump performance, while the mechanism is unclear. To solve this problem, we studied the vortex structures under different conditions and focused on the relationship between vortex characteristics and performance parameters. It was found that the mechanism for the vortices affecting the pump was triggering nonaxial inflow at the impeller inlet and inducing higher entropy production in the passage where the vortices possessed. Based on our further research, it was clear that backwall vortices were nonnegligible and should be eliminated in the circumferential direction near the shroud of the impeller.