Experimental Study On The Wake Interference Flow And Pressure Pulsation In A Centrifugal Pump

The pressure pulsation induced by the blade-tongue interaction and the wake flow at the outlet of the blade is an important factor in the vibration and noise of the centrifugal pump.A single-stage single-suction centrifugal pump was used as the research object under the support of the National Natural Science Foundation of China(the eddy dynamic characteristics of pump forced turbulence and its excitation mechanism NO: 51576090).Based on PIV measurement and pressure pulsation experiment,the interferential flow and pressure pulsation characteristics of the waketongue interaction in the centrifugal pump were investigated;The blade trailing edge is modified and the influence of the shape of the trailing edge of the blade on the pressure fluctuation of the pump is studied through the pressure pulsation experiment,which provides a useful reference for the optimization design and the noise reduction of the centrifugal pump.The main work and results of this article are as follows:1.The PIV measurement captures the flow field information during the blade sweeping the tongue under different operating conditions.After data processing,the time-averaged absolute velocity field,time-averaged relative velocity field,timeaveraged vorticity field,and POD mode information are obtained.Based on this,the interferential flow characteristics of the wake-tongue interaction are analyzed.The results show that the wake vorticity can clearly indicate the rotor-stator interaction between the wake and the tongue.The wake vortex is composed of positive and negative vortices.The positive vorticity is from the pressure surface of the blade,and the negative vorticity is from the suction surface of the blade.Both of them are symmetrically distributed around the circumference of the impeller outlet.When the wake sweeps across the partition tongue,the wake vortex and the partition tongue collide with each other,resulting in separation and shedding high vortices.The flow rate has a significant effect on the wake vortex range and the size of the vortex shedding.It decreases first and then increases with increasing flow rate.The wake vorticity is the minmum at 1.0 Qd.The POD modal energy and fluctuating velocity field show that the pulsation velocity is different from the average velocity by 2 orders of magnitude,and the distribution of the pulsation velocity is random.2.Pressure pulsation measurement points are arranged in the circumferential direction of the volute and the inlet and outlet of the pump.The pressure pulsation signals of each measuring point under different operating conditions are measured experimentally.The influence of the wake flow in the centrifugal pump on the pressure pulsation and the relationship between them are explored.The results show that the time-domain signal shows that the pressure pulsation has a periodic variation characteristic,and the fluctuation of the pressure pulsation amplitude varies significantly under different operating conditions.The pressure pulsation energy in the spectrum is mainly within 4 times the blade passing frequency,it is the main frequency and the amplitude is much larger than other frequencies.The amplitude of pressure fluctuation at the blade passing frequency and the RMS value of the pressure fluctuation all showed waveform changes in the circumferential direction of the volute,and the fluctuation range first decreased and then increased with increasing flow rate.The fluctuation range was the minmum at 1.0 Qd.With the increase of flow rate,the pressure fluctuation energy of the whole pump first decreases and then increases.At 1.0Qd,the pressure fluctuation of the entire pump is the weakest,which means that the pressure fluctuation is obviously enhanced in the partial operating condition,it is indicated that the partial pressure operation will be obviously enhanced,the far deviation from the design condition,the stronger of the pressure pulsation.The variation of pressure pulsation with flow basically shows that the wake vortex intensity is consistent with the change of flow rate,that is,the wake vortex intensity is closely related to the pressure pulsation intensity;and the fluctuation of pressure pulsation in the volute case also indicates the wake vortex is non-axisymmetrical in the circumferential direction and the vorticity is not the same everywhere.3.Thinning of the trailing edge of the original blade and slant cutting 15°,25°,and 35° of the blade,4 time modifications in total,to explore the effect of blade trailing edge shape on wake flow and pressure pulsation of model pump.The results show that the thinning of the trailing edge of the blade can weaken the pressure pulsation of the entire pump under large flow,and the three schemes for cutting the trailing edge of the blade can reduce the pressure pulsation level of the entire pump from the dead point to the range of 1.6 Qd.The 25° solution is optimal.It shows that the blade trailing edge cutting can effectively reduce the wake vortex intensity.