L10: A FEM Approach to Predict Acoustic Resonance in Multistage Centrifugal Pump

Abstract

LecturesAcoustic resonance can develop within the hydraulic channels of the pump, especially in the long crossover channel of a multistagecentrifugal pump This phenomenon occurs when the hydraulic channel length is equal to the sound wavelength produced by theBlade Passage Frequency (BPF) The combination between the BPF and the wave reflection from a stage to the next, generates anamplification of pressure pulsation and eventually a higher vibration level in the pump This paper presents a Finite Element Method(FEM) approach to predict the acoustic resonance in multistage centrifugal pumps The 1-D method used to calculate the equivalentlength through the channel, assuming it as a straight pipe, has demonstrated in some cases that it is unable to predict the vibrationproblem related to the phenomenon of the acoustic resonance that occurred in the centrifugal pump test bench with complex 3-Dgeometry, therefore the study of a new methodological approach began The most important parameter to be evaluated is theequivalent channel length which is the length of the sound wave path within a complex 3D geometry The FEM analysis performed byANSYS® for the calculation of harmonic resonance of the hydraulic channels has been used to predict the possible acoustic resonancein long crossover channels of API 610 BB3 (multistage centrifugal pump, axially split, between bearings) centrifugal pumps The useof Acoustic Analysis coupled with the Harmonic Analysis implemented in ANSYS® allows to simulate the wave propagation andreflection in a complex 3-D channel and obtain the harmonic response of the machine To validate the tool, several simulations havebeen done on BB3 pumps, already tested in the past: the analysis showed a very good correspondence between the FEM results andthe vibration reports of real pump tests The new procedure was able to verify both the pumps that showed vibration problems and thepumps without problems A detailed case study also demonstrated that the accuracy of the analysis method can detect the change insystem behavior when a change in fluid temperature is measured After this series of simulations and comparative analysis, the newapproach has become the standard procedure for detecting vibration problems related to the acoustic resonance during the designphase and avoiding possible issues in the witnessed performance tes