Study of the Tonal Casing Noise of a Centrifugal Fan at the Blade Passing Frequency. Part I. Aeroacoustics

摘要

This paper is concerned with the simulation of the unsteady turbulent flow and the aerodynamic tonal noise due to pressure fluctuations on the casing wall. Three-dimensional numerical simulations of the complete unsteady flow on the whole impeller-volute configuration were carried out using computational fluid dynamics (CFD) techniques. Pressure fluctuations on the casing wall were obtained, and the blade passing frequency (BPF) component was extracted to be modeled as the dipole source term of the wave equation. In a companion paper, the pressure fluctuations served as the external excitation to the casing vibration. Multi-domain direct boundary element method (BEM) was used to simulate the noise radiation with two domains representing the interior and exterior fields of the volute respectively, in order to take account of the sound scattering effect by the volute casing. Results showed that the dipole on the volute tongue surface was the most dominant noise source of the fan. Slopingedge volute tongue was introduced to reduce BPF noise radiation through phase cancellation between the dipole sources over the volute tongue.