Study Of Flow Induced Radiated Noise In A Multi-Stage Centrifugal Pump

This study is supported by National Natural Science Foundation of China“Study on the Mechanism of Distortion Flow Induced Noise in Centrifugal Pump”(51509108),Jiangsu Province Natural Science Fund “Study on Low-noise Hydraulic Optimization Design and Key Technology of Centrifugal Pump”(BK20150516),and China Postdoctoral Science Foundation “Research on Structure-induced Noise Analysis and Acoustic Optimization Design of Multistage Centrifugal Pump”(2015M581735).Multi-stage centrifugal pump is an important equipment to provide high-head and high-pressure when transport liquid,and it's widely used in water supply of high building,desalination,deep-sea oil extraction and other important areas of national economy.Due to the complex flow in centrifugal pump,and there are inter-stage coupling problems in the multi-stage centrifugal pump,which often accompanied by vibration and noise during its operation.In recent years,with the improvement of people's living standards and the pace of urbanization in China,people have put forward more and more stringent requirements of working and living environment.While noise pollution has been one of the four major pollution with air pollution,water pollution and waste pollution,therefore,the noise problem has gradually been widely concerned by many areas.Based on the prototype,the model pump is designed and the numerical simulation of the flow field and sound field are carried out in this paper.The external characteristics and radiation noise experiment are completed on model pump in the semi-anechoic chamber.The study has revealed some laws of the change of internal flow and radiation noise of multi-stage centrifugal pump.Based on the numerical calculation and the experimental results,the optimal relationship between impeller and guide vane matching is designed,and then the calculation of flow field and sound field are carried out on the optimized multi-stage centrifugal pump,and then analyzed the influence of impeller and guide vane matching on radiated noise.The main work and achievements of this paper are as follows:1.This paper briefly introduces the noise distribution of multi-stage centrifugal pump and system analysis research status at home and abroad on noise.The model pump is obtained by simplify the prototype,and the steady and unsteady numerical calculation of the multistage centrifugal pump are carried out,and then analyzed flow field distribution and pressure fluctuation characteristics of multi-stage centrifugal pump,which showed that the performance prediction of simulation are basically agree with the experiment data of multi-stage centrifugal pump,the relative error of the head is 4.5%,the relative error of efficiency is 3.8%.At the same flow rate,from the first impeller to the last impeller,the inflow conditions of impellers gradually deteriorated,and the multi-stage centrifugal pump have more vortexes at 0.6Qd.With the increase of flow rate,the number of vortex gradually reduced in impellers and guide vanes.The results of pressure pulsation show that the guide vane have the largest pressure pulsation intensity and the smallest in impellers,and the difference of pressure pulsation intensity between the measuring points is large.The main frequency of pressure fluctuation is blade passing frequency(327Hz)in vanes,while at the small flow rate condition,and there are more than the low frequency pulsation.2.When completed the unsteady simulation flow field,the numerical simulation of flow induced radiation noise of multi-stage centrifugal pump is carried out based on the acoustic finite element method(FEM),and analyzed radiated noise between numerical simulation and experiment under different flowrate,which indicate that the main frequency of radiated noise is BPF.With the increase of the flow rate,the total average sound pressure level of the radiated noise decreases first and then increases,reaching the minimum level near 0.8Qd condition.The maximum sound pressure levels located near the first stage while the minimum sound pressure level near the last stage.Under different flowrate conditions,the directivity of the radiated noise of the multi-stage centrifugal pump shows the dipole characteristics at BPF.3.The flow induced radiated noise test of multi-stage centrifugal pump was built in the semi-anechoic chamber,and the radiated noise experiment was conducted based on the external characteristic experiment of the pump,with the increase of flowrate,the result suggested that the radiated noise level of the pump first increase then decrease and increase with and without motor enclosure.The sound pressure level reached the maximum value at the 0.8Qd and the minimum value at the 1.2Qd.With and without the motor enclosure condition,the difference of sound pressure level is about 2dB.With the linear increase of pump running speed,the total sound pressure level of multi-stage centrifugal pump radiated noise is also linearly increasing.The radiated noise directivity of multi-stage centrifugal pump shows that it has characteristic of dipole,which indicate that the dipole source is the main noise source of multi-stage centrifugal pump.4.Based on the numerical calculation and experiment of the model pump,the matching relationship between impellers and guide vanes are optimized,and then completed the numerical calculation of flow field and sound field.The result of calculation show that the head of the optimized multi-stage centrifugal pump was improved by 19.2% and the efficiency by 19.32% at the design flow rate,moreover,the best efficiency point was near 1.1Qd,and the high efficiency area was wider.The velocity distribution of the optimized multi-stage centrifugal pump was more uniform and it has fewer vortexes in impellers and vanes.The pressure pulsation intensity of the optimized pump at the same position is reduced compared with that of the model pump,and the pressure fluctuation between the measuring points is relatively gentle.The sound field simulation show that the main frequency of the radiated noise is BPF as well while the sound pressure level at BPF decreased by 2d B and the overall sound pressure level decreased by 3.5d B,which indicates that the optimization method used in this paper is effective for multi-stage centrifugal pump noise reduction.