| The Centrifugal pumps with semi-open impellers are widely used in many fields of the national economy.When operating at low flow conditions,flow separation will occur in the impeller,which will induce unstable flows such as backflow vortices and stall vortices.Especially due to the existence of tip clearance,the interaction between the leakage flow and the separated flow and secondary flow in the impeller makes the pressure pulsation and vibration problems more prominent,which aggravates the energy dissipation and affects the operation stability of the pump.In order to solve this problem,three kinds of slit end wall structures were designed on the front cover plate,and the mechanism of external characteristics,internal flow and pressure pulsation of different slit structures was studied.The orthogonal experiment method was used to analyze the influence factors of inclined slit,and the influence law of geometric parameters on pump performance was clarified.The main research results are as follows:(1)The head of the pump will decrease slightly due to the three kinds of end walls of the arc seam,the inclined broken line seam and the inclined seam,but the efficiency of the whole pump can be improved,especially the inclined seam structure,which is more obvious in the design condition and the large flow condition.At the same time,it can suppress the hump characteristics under the small flow condition and improve the operation stability of the centrifugal pump.(2)The slotted endwall can effectively improve the unstable flow in the impeller under small flow conditions.As the flow rate decreases,the prototype inlet reflux is serious,the reflux ratio increases,and the distance to the inlet pipe is farther and farther,and the crowding out effect on the mainstream is enhanced,resulting in an increase in the entropy yield of the inlet section.The slotted endwall can suppress the sudden change of the circulation at the tip clearance of the impeller inlet,reduce the inlet angle of attack,reduce the impact loss,and suppress the tip leakage flow of each working condition,weaken the influence of the leakage vortex on the mainstream in the flow channel,so that the area of the low-speed zone in the flow channel is significantly reduced,thereby inhibiting the backflow and increasing the flow capacity of the flow channel.(3)The slotted end wall can reduce the pressure pulsation.Under the condition of small flow rate,due to the influence of inlet reflux,the pressure pulsation in the inlet pipe has low frequency and high amplitude pressure pulsation,and the closer to the impeller inlet,the larger the amplitude.The slit end wall can suppress the pressure pulsation in the inlet pipe,so that the amplitude is greatly reduced,which is about one fifth of the original.Under the design condition and the large flow condition,the low-speed vortex area in the impeller decreases,but the arc gap will cause the increase of the amplitude of some measuring points.(4)The orthogonal experiment method is used to optimize the number,position and inclination angle of the inclined slot.Through the range analysis,it is found that the position of the slot has the greatest influence on the efficiency.The factors that have the greatest influence on the head under different working conditions are not the same.The optimal slotting scheme is determined by the comprehensive balance method.This scheme makes the highest efficiency point move to the large flow condition point,and the efficiency and head of the design condition and the large flow condition are increased.In addition,the low-speed zone near the tip clearance is significantly improved,the flow in the impeller is more stable,and the tip leakage intensity is significantly reduced. |
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