Investigation Of The Characteristics And Suppression Method Of Tip Leakage Vortex In A Semi-open Centrifugal Pump

The tip leakage flow in a semi-open centrifugal pump is very important for the hydraulic performance,which easily leads to the decrease in performance,increase in pressure fluctuation and aggravating of the vibration.In this paper,the tip leakage flow of a semi-open centrifugal pump was studied,and the characteristics of the tip leakage vortex and pressure fluctuation were analyzed.The methods of controlling the tip leakage fow by circumferential groove,T-shaped blade and their coupling were proposed,and the flow control mechanism was analyzed.The research provided new methods to suppress the tip leakage flow and improve operation stability in semi-open centrifugal pumps.The main work was as follows:First,the characteristics of tip leakage vortex were studied.The vortex structure in the impeller was remarkably affected by operation condition.Under large flow rate condition,the initial position of tip leakage vortex was close to the middle of blade,and the secondary tip leakage vortex was formed at the trailing edge.The tip leakage flow with a large velocity gradient at the tip clearance leaded to the high entropy production rate and pressure fluctuation with high amplitude.The initial position of tip leakage vortex moved upstream with the decrease of flow rate.The circumferential movement trend of tip leakage vortex increased under low flow rate condition.Then,the tip leakage vortex broken down in the leading edge of adjacent blade,and the reverse flow vortex and passage vortex appeared.The pressure fluctuation was further enhanced.The improved tip leakage vortex migration trajectory prediction model was proposed by the analysis of the tip leakage vortex characteristics.The model can expand the prediction range and increase prediction precision.Second,the circumferential groove was proposed to suppress the effect of tip leakage flow on flow field of a semi-open centrifugal pump.The circumferential groove made the initial position of the leakage vortex move downstream,and provided a channel for the tip leakage flow,which could quickly pass through the groove rather than form the leading edge overflow,and reduced the relative flow angle at the blade inlet and weakened the trend of the tip leakage flow to upstream,and suppressed the reverse flow by increasing the axial velocity and decreasing the circumferential velocity.The flow field was improved,but the head and efficiency decreased.The circumferential groove could effectively improve the pressure fluctuation under design and large flow rate conditions.Standard deviation of unsteady pressure near the tip clearance decreased.The circumferential groove improved characteristic frequency induced by reverse flow under low flow rate condition,but resulted in the slight increase of pressure fluctuation on pressure surfaceThird,the T-shaped blade was proposed to control the tip leakage flow for the effect of tip clearance to hydraulic performance in a semi-open centrifugal pump.T-shaped blade could reduce hydraulic loss,increase Euler head,and improve the head and efficiency.The relative flow angle near the tip clearance of the T-shaped blade decreased,and the strength of the backflow region and low-velocity region remarkably weakened,and the blockage in the tip clearance decreased.The area of the high entropy production region decreased,and trend of upstream diffusion was restrained under design condition.The T-shaped blade could inhibit the diffusion of the high entropy production region to the hub under low flow rate,but the entropy production and mixing losses at the tip clearance slightly increasedFinally,the exploration on the coupling effect of circumferential effect and T-shaped blade was carried out to solve the problem between circumferential groove and T-shaped blade,which cannot improve the hydraulic performance and pressure fluctuation at the same time.The coupling method could combine the advantages of circumferential groove and T-shaped blade,improve the unstable flow,reduce the tip blockage and suppress the reverse flow vortex without reducing the efficiency and head.The coupling method made the standard deviation of unsteady pressure decrease.The amplitude of the main frequency and other characteristic frequencies at leading edge decreased remarkably.The coupling method could effectively suppress the pressure fluctuation and improve the operation stability.