Numercial Simulation And Fluid-solid Coupling Analysis Of Cavitation On Centrifugal Pump Impellers

Centrifugal pump is an important general fluid machinery which relates to the base of national economy.Cavitation is an important factor to restrict the performance of centrifugal pump and its development.Not only the centrifugal pump,many kind of turbomachine will lead to performance degradation mechanical vibration and noise due to cavitation,even lead to damage to the machine.So it is very important to solve the cavitation problem.In the working process of the centrifugal pump,the partial pressure of the impeller is decreased,especially the impeller inlet.Cavitation occurs when the impeller inlet pressure is reduced to the saturated vapor pressure.The existing research results are mainly divided into two kinds of methods to solve cavitation,one is to raise the inlet pressure,another is to optimize the impeller.Because the pipeline installation and use of the pump operating conditions are difficult to limit,this paper mainly through the impeller design,with numerical simulation method to study on centrifugal pump impeller cavitation.The main work and experimental procedure are as follows:1?To study on the impeller influence of centrifugal pump cavitation.Using Ansys bladegen under the same meridional plane flow path,and the same type of 3D impeller designed four kind of impeller number,four kind of wrap angle and four kind of entrance blade angle.Then I use Pro/e to model the 3D impeller.2?In order to simulate the flow field of the centrifugal pump,it is necessary to model the inlet and diffuser(volute).Diffuser is also an important component,which plays the role of converting the kinetic energy of the medium into the static pressure energy.Finally,each part of the centrifugal pump will be assembled.3?Using the numerical simulation software CFX simulates the whole flow field and cavitation.First of all,in order to determine the optimal grid number,I made a analysis of grid independence.Then this paper used multi-phase unsteady cavitation model to simulate the flow field in the centrifugal pump.Pressure inlet and mass flow outlet will be used to adjust NPSHa.The Rayleigh-Plesset equation was used to describe the bubble formation and collapse.I chose SST turbulence model and multiple reference frame to deal with the the static and dynamic coupling interface between rotating impeller and volute.Finally we can get the distribution of the centrifugal pump impeller cavitation,pressure distribution contours,velocity vector diagram and streamline diagram,and predicted the characteristic parameters of centrifugal pump by the internal functions.By comparing and analyzing the cavitation characteristics of the three types of blade impeller,I got the law of the bubbles distribution inside the centrifugal pump impeller.Experiment results show that:(1)Centrifugal pump cavitation is produced in the impeller inlet and developed along the back of the blade.(2)When the centrifugal pump blade number was too little,the flow was not good,and the bad secondary vortex would block the flow channel.Although more blades can increase energy transmit,it also can cause much mechanical loss.The simulation results showed that the 7 blades impeller had the best performance.(3)The blade wrap angle had influence in the shape of the impeller flow channel,which affects bubble development and diffusion.The simulation results showed that the impeller of 120° wrap angle had the lowest bubble content.(4)The shape of blade inlet is mainly influenced cavitation generation.The less entrance angle is,the blade inlet will be more winding,and the turbulence will be more serious.And then lead to local pressure drop acceleration cavitation.4.centrifugal pump impeller and fluid-structure interaction analysis is to analyze impeller load and vibration in the case of pre-force.The flow field pressure would be loaded onto the impeller with different parameters in the NPSHa=2m,Q=21kg/s,r=1450r/min working condition.The experiment could verify the strength of the impeller under the pressure whether or not meet the statics.Then I would analyze the vibration characteristics of the impeller rotor.The results show that the natural vibration frequency of the impeller is much less than that of the working frequency of the impeller.