Numerical Study Of The Flow Fields In A Centrifugal Pump Impeller At Two Non-Conventional Working Conditions

With the development of computational fluid dynamics(CFD)technology,the reseach and design of centrifugal pump more and more closely are combined with the application.It has become an important reseach method and direction to study the internal flow in the centrifugal pump and then optimize the design with the simulation results.In this paper the steady flow phenomena and characteristics were analyzed,three dimensional flow field of low specific speed centrifugal pump impeller is studied by numerical simulation,and the results are compared with the published experimental results.Numerical study of the flow fields characteristics of the non-Newtonian power-law fluid and stall in a centrifugal pump impeller are two non-conventional working conditions.The main work and the achievements in this paper are as follows:1.By critical review the trend of the inner flow numerical simulation for centrifugal pumps,the main flow phenomena in centrifugal pumps was thoroughly analyzed.The numerical simulation models and computational methods for three-dimensional(3D)viscous turbulent flow in the centrifugal pump were introduced.2.Numerical simulation of the steady of the centrifugal pump impeller was studied.Four turbulence models,namely:the Standard k-? model,Realizable k-? model,RNG k-?model and Reynolds Stress Models(RSM)are employ respectively,and combined with the SIMPLEC pressure-correction technique on a non-staggered gird arrangement were employed.Then the numerical simulation of the 3D viscous turbulent flow in the internal flow field of impeller is carried out.This numerical simulation model was proved to be accurate for engineering through the comparisons between the simulation results and PIV experimental results in the literature.The distribution of the velocity,pressure and turbulent intensiy of the flow in the impeller at defferent flow conditions were showed and compared,which reveals the flow field structure of the centrifugal pump impeller,get the head curve and the experimental results obtained in the four kinds of turbulence models under the basic trend,show the feasibility of the simulation method.Four turbulence models,at the small flow rate,the error of two kinds of turbulence models of RSM and Realizable k-? model is small.But when the flow rate Q>0.8Qd,the error of Standard k—? model is the lowest;In the grid and convergence index,the four models,the convergence time of the RSM is far more than the other turbunence models and computational eficience is lowest.At the same time,in the two equation turbulence model,Standard k-? model calculation efficiency is the highest,and can accurately reveal the flow field of the basic characteristics,suitable for engineering calculation is adopted.3.Stall often occurs at part load condition in the centrifugal pump.In this paper the computation model for stall flow in the centrifugal pump impeller is builted.The current study assesses in the influence of steady-state Standard k-? model suitable for predicting stall phenomenon in pump impeller and the numerical results are with satisfactory agreement confirmed by PIV/LDV experimental results.This paper also found that the basic information flow by double channel model can be concluded to stall,numerical the flow in the impeller and the actual details of the good agreement.4.The flow of water and non-Newtonian power-law fluids(CMC)were compared in the numerical simulation of the flow fields in the centrifugal pump impeller.The velocity and pressure distribution of two kinds of flow media on the impeller are obtained.The results show that the internal pressure and the velocity of the centrifugal pump impeller are basically the same as that of the tap water when the non-Newtonian power-law fluids are used.Through the analysis of the total pressure coefficient,the value of Cp of PS and SS are different,and this different value is defined as ?Cp,show that:the ?Cp of power-law fluid(CMC)was smaller the ?Cp of tap water.It may therefore be concluded that:compared with the transport of water condition,in the transport of non-Newtonian power-law fluid the power of the impeller increased.The reseach method of mechanism loss of the transfer system can not know the specific source and increase process of the local loss.Dissipation function can directly reflect the source of centrifugal pump impeller loss,and it is an important parameter to study the mechanism of centrifugal pump impeller.For the head loss,with the increase of the flow rate,the fluid friction loss of power-law fluid increases as solutions concentrations grow,and the total pump head for power-law cases is smaller in comparision with that the tap water case.Different the working medium of water and CMC,by study the dissipation function and total head loss,it can be clearly seen that the transmission of non-Newtonian power-law fluid loss than the delivery of Newtonian water fluid much more,and this is one of the reason why the pump head is lowered.In addition,the results of turbulent kinetic energy and vorticity was studied,also show that the loss for the non-Newtonian power-law fluid case is higher in comparison with that for Newtonian tap water case.