Simulations and Experimental Investigations on the Acoustic Characterization of Centrifugal Pumps of Different Specific Speed

Christian Lehr,Andreas Linkamp,Andreas Brümmer,Daniel Aurich

doi:10.3390/ijtpp4030016

Christian Lehr, Andreas Linkamp + Show 2 more

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https://doi.org/10.3390/ijtpp4030016

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Abstract

Subject of discussion are simulations and experimental investigations on the acoustic characterization of three single stage centrifugal pumps of different specific speed. In operation, these pump-types generate pressure pulsation at blade passing frequency, primarily due to rotor-volute-interaction. In order to determine the acoustic excitation it is necessary to know about the pumps’ acoustic transmission parameters. In this paper, a one-dimensional numerical model for transient time-domain simulation is presented, which takes into account the pump geometry as well as the volutes’ structural behaviour by means of the local effective speed of sound. Numerical results for the transmission characteristics of the three different pumps are shown in terms of scattering matrices and evaluated against parameters calculated from measurement results. The experimental analyses are carried out using dynamic pressure sensors in both the suction and the discharge pipe. Assuming solely plane wave propagation, the complex acoustic field on each side is evaluated independently. The so called “two source” method is then used to determine the transmission parameters of the pumps in standstill for a range of frequencies experimentally. Subsequently, the acoustic excitation at varying rotational speed is evaluated by means of measurements at the pumps in operation and presented as monopole and dipole source types for cavitation-free conditions.

Highlights

The pressure and velocity pulsations in centrifugal pumps can be attributed to a non-uniform pressure and velocity distribution along the impeller outlet and an amplification of these conditions caused by an interaction with the volute tongue or rather the surrounding guide vanes [1,2]
In order to determine the acoustic excitation caused by centrifugal pumps from dynamic pressure measurements, the transmission behaviour of the pump must be known
It becomes apparent that the effective speed of sound ae f f,ch, to model the pumps’ structural compliance due to pressure pulsations, was small compared to the pure fluid and increases significantly with the value of specific speed ns

Summary

Introduction

The pressure and velocity pulsations in centrifugal pumps can be attributed to a non-uniform pressure and velocity distribution along the impeller outlet and an amplification of these conditions caused by an interaction with the volute tongue or rather the surrounding guide vanes [1,2]. The source strength significantly depends on the pumps geometry [3,4] and operation parameters as rotational speed and operation point [5,6]. The occurring pressure amplitudes in connected pipe systems due to this source of sound are influenced by the acoustic impedance of the piping [7] just as the pumps transmission behaviour itself. In order to determine the acoustic excitation caused by centrifugal pumps from dynamic pressure measurements, the transmission behaviour of the pump must be known. Provided that wave propagation is linear and plane, a centrifugal pumps transmission characteristic can be described as an acoustic four-pole and by means of four parameters.

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