Numerical Simulation And Prediction Of Cavitation Flow In The Whole Flow Passage Of A Centrifugal Pump

In the operating process of centrifugal Pumps,cavitation may cause corrosion to its flow parts,produce noise and vibration.If the cavitation is serious,the mechanical efficiency will drop remarkably,even cannot function normally.Therefore,how to improve the suction performance of centrifugal pump is an important research aspect in the field of fluid mechanism.With the development of computational fluid dynamics and rapid improvement of computer capacity,it has been possible to research the inner flow inside centrifugal pump by numerical simulation.Numerical simulation can estimate the parameters that are difficult to measure in experiment.In the analysis and engineering design process of fluid machinery, numerical simulation improves reliability and reduces the cost significantly.Numerical method has become an important tool to design centrifugal pump.Based on hydromechanics computation knowledge,taking commercial CFD so,ware Fluent as tool,using RNGκ-εtwo equations model of Reynolds averaged method,mixed multiphase flow model,cavitations model and SIMPLEC algorithm are applied to simulated and predicted the cavitation flow in an impeller of a specific speed n_s=91.9 centrifugal pump.Through simulation,cavitation flow situations of the velocity,pressure and cavitation volume fraction distribution are obtained which have vital significance to the impeller optimized design.The results of the simulation show that using the cavitations models can reflect the cavitations flow in the pump.The result indicates that:1)Do simulation for the cavitation flow in whole flow passage of centrifugal pump,we can see that it is without obvious cavitation happens in inlet and spiral case section,but cavitation in impellers mainly takes place in the inlet later on place of black blade,closing to the front cover,there is obvious lower pressure zone exists in this position;2)With a large flow working condition, the surface area in impeller lower pressure zone and cavitation volume fraction are all larger than the design working condition and small flow working condition,it indicates that with the large flow working condition,it's easy to cause erosion damage;3)In unsteady cavitation turbulent flow simulation,the impeller within a rotationally periodic,in pace with time goes, the change condition of rotationally periodic is a unsteady change process which from weak to strong and from strong to weak.But the place of a single blade where erosion is most serious is a little behind black blade and contact the front cover,outlet edge blade vicinity of blade has no obvious erosion phenomenon.This simulate result is in accord with the result about steady cavitation flow;4)Within the cavitation happening process,along with the reduction of NPSHA,Cavitation volume fraction in impeller increases gradually,blade's surface pressure and Cavitation volume become not well-distributed,head H and efficiencyη_h appear to descending trend.It illustrates that serious cavitation can affect performance of pump.This pump's head at different flowrates are calculated to analyze the veracity of numerical simulation.It is found that the error is less than 5%compared with the experiment results under design flowrate(45.7 m~3/h)This result indicates the result of numerical simulation is acceptable.