Study of the Tonal Casing Noise of a Centrifugal Fan at the Blade Passing Frequency

Abstract

This paper studied the casing vibration and noise radiation of a centrifugal fan at the blade passing frequency (BPF) induced by the internal unsteady flow. Three-dimensional numerical simulation of the complete unsteady flow in the whole impeller-volute configuration was carried out using computational fluid dynamics (CFD) techniques. Pressure fluctuations on the casing were obtained, and the BPF component was extracted after Fast Fourier Transform (FFT). In Part I of this two-part study, the BPF pressure fluctuation was modeled as aeroacoustic dipole source according to Lighthill's acoustic analogy theory, and sound propagation was simulated regarding the casing as a rigid body. In this part, the casing was modeled as an elastic structure in order to study the tonal vibroacoustics of the casing structure with the BPF pressure fluctuations as excitation. Time harmonic response of the casing was calculated using the finite element method (FEM) and vibroacoustic noise radiation was analyzed by the boundary element method (BEM). The primary objective is to make an attempt to quantitatively evaluate the flow-induced casing vibration and noise radiation in fluid machinery. Some results were obtained casting light on the characteristics of casing vibration and noise radiation.