A numerical study of flow-induced noise in a two-dimensional centrifugal pump. Part II. Hydroacoustics

This paper is concerned with determination of the acoustic pressure field in a centrifugal pump. The main noise-generating mechanism is assumed to be the unsteady impeller blade surface forces, which reach a maximum when the flow channel between two consecutive blades is shut off by the volute tongue. The acoustic sources are moving (rotating) dipoles. The strengths of these dipoles are estimated by using the discrete vortex method described in Part I of this two-part study, but may be determined by any other (appropriate) flow analysis method. The solution to the inhomogeneous wave equation which describes the generation and propagation of pressure waves is expressed in the frequency domain, by making use of Fourier transform. The dipole-type boundary term, which accounts for the scattering from the volute, is discretized by employing the boundary element method. The emphasis is on a two-dimensional procedure, but extension to three dimensions is also discussed. The method is applied to the flat 'two-dimensional' laboratory centrifugal pump considered in Part I. The frequency-domain solution is particularly useful for this kind of problem, as the interest typically is in the dominating frequency components only, which are the blade passage frequency f(blade) and its higher harmonics, 2f(blade), 3f(blade), etc. The numerical results are compared with available experimental results, by which they are well supported. The frequency-domain solution is also found to be very useful in connection with minimization of the flow-noise by design optimization. (C) 2004 Elsevier Ltd. All rights reserved.