Calculation And Control Strategy Of Centrifugal Pump Fluid Excitation

In this paper,a single-stage single-suction centrifugal pump with a specific speed of 63 is used as the research model.The characteristics of performances,pressure pulsation,flow field and pressure pulsation of the pump under different speed and flowrate are studied by the means of numerical simulation.The influence of different ways to change the gap between the impeller and the tongue on the characteristics of performances,pressure pulsation,flow field and pressure pulsation of the pump has been well studied.The research contents of this paper include the following five aspects:1.Unsteady characteristics of downstream pipe of the 90° pipe bendTaking the flow area of 90° pipe bend and its up stream and downstream pipelines as research model,the unsteady characteristics of 90° pipe bend under different inflow velocity,different pipe diameter and different bend centerline radius was studied.The results show that the separation of boundary layer in the elbow is the key factor influencing the downstream flow of the elbow.The large scale coherent structures generated after the separation point dominate the local flow and propagate and dissipate along the downstream direction.The position of the separation point does not change significantly with the inlet velocity and the pipe diameter.The inflow velocity and the curvature of the elbow affect the flow characteristics and wall pressure fluctuation characteristics of the pipe downstream.The pres sure fluctuation of the downstream pipe with a small curvature of 90° pipe bend is significantly lower than that of the large curvature.2.Influence of 90° pipe bend on external characteristics and pressure fluctuation of downstream centrifugal pumpThe differences of the characteristics of performances,pressure pulsation,flow field and pressure pulsation of the pump under the optimum condition with straight pipe inflow and elbow flow was analyzed.The flow characteristics of the inflow pipe,the different characteristics of the performance and the internal flow of the pump with different distance between the elbow and impeller were analyzed.The results show that there are interactions between the flow of the impeller and the downstream of the elbow.For example,when the distance between the pump and the 90° pipe bend L is equal to zero,the boundary separation at the small radius of the 90° pipe bend is suppressed.The head and efficiency of the pump with 90° pipe bend are higher than those with the straight pipe.The characteristics of nonuniform inflow of the pump change with the L.The 90° pipe inflow does not have a significant influence on the mean radial force of the volute and the impeller,but the amplitude of the radial force pulsation of the volute changes with the distance between the 90° pipe bend and the impeller.3.Pressure fluctuation characteristics of centrifugal pump with straight pipe inflow working in different flowrate and speedThe pressure pulsation characteristics of the pump with straight pipe inflow under different rotational speed and flowrate were studied.First,the numerical simulation results of pump performance were compared with the experiment data,and the factors that made the difference between the numerical simulat ion results and the experimental results were analyzed.Then the radial force characteristics were analyzed.The results show that the normalized radial force of impeller and volute changes linearly with the flow coefficient.The minimum value of radial fo rce of impeller and volute appears in the optimum condition and its similar working condition.The change in tongue pressure difference is different from the radial force.The lowest value of the pressure difference of the tongue appears at 0.8 times the o ptimum point and its similar working conditions.The main frequency of Radial force and tongue pressure difference are blade passing frequency and its harmonic frequency.The spectral characteristics vary with shaft speed and flowrate.The correlation anal ysis between the pressure difference of the tongue and the upstream and downstream flow parameters shows that there is a certain correlation between the pressure difference of the tongue and the downstream flow of the tongue.At the flowrate of 0.8 times t he optimum condition,this correlation is no longer obvious.4.Pressure fluctuation characteristics of centrifugal pump with 90°pipe bend inflow working in different flowrate and speedThe pressure pulsation characteristics of the pump with 90°pipe bend inflow under different rotational speed and flowrate were studied.The pressure fluctuation characteristics with the straight pipe inflow and with the 90°pipe inflow were compared with each other.The results show that the performance and the pressure dif ference of tongue show no difference between pump with 90°pipe bend inflow and with straight pipe inflow except when pump working in the design speed and 0.8 Qopt.When working at design shaft speed with the flowrate of 0.8 Qopt,the pump with the 90°pipe inflow has three times the amplitute of tongue pressure difference of the one with straight pipe inflow.The mean and pulsating amplitude of the radial force of the impeller and the volute show no significantly different with different inflow conditions.Whe n the working condition deviates from the optimum condition,the influence of the small-scale flow structure came from pump's inlet is still present in the volute.The correlation between the pressure difference of the tongue and the flow parameters of upstream or downstream shows that when the flowrate reaches 0.4 Qopt,the flow which influence the tongue pressure difference has affected the flow in the downstream area of the volute.5.The influence of three different ways to change the gap between the i mpeller and the tongue on the characteristics of pressure pulsationThe amplitude of pulsation of the radial force of the impeller and the volute,the amplitude of the pressure difference of the tongue and the pump efficiency decrease gradually with the increase of the diameter D3 of the volute.When the gap 2c /D2 is greater than 5%,the decline of pump efficiency is gradually faster than the radial force pulsation amplitude.By changing the radial position of the tongue to change the gap between the impeller and the tongue,the efficiency of the pump and the volute is generally lower than the efficiency value by changing the diameter D3 of the volute.Using this approach to slightly reduce the gap can reduce the amplitude of the radial force.Cutting and extending the tongue can make the pump efficiency down.In accordance with the law of the flow of the volute to extend the tongue can effectively improve the passing through ability of the volute.The cutting tongue can effectively improve the the passing through ability of the volute in the design conditions and high flowrate conditions.