Analytical Modelling of Wake-Interaction Noise in Centrifugal Compressors with Vaned Diffuser

Abstract

The paper is dealing with the upstream propagation of wake-interaction noise in a subsonic centrifugal compressor with a vaned diffuser. The acoustic sources on the diffuser vanes, not investigated here, are assumed to force pressure patterns that are determined by the compared numbers of blades and vanes and the impeller rotation speed. The corresponding acoustic modes of propagation in the radial duct embedding the vanes and impeller trailing edges are derived assuming a locally two-dimensional, potential, spiral base flow and briefly discussed. Then, a mode-matching technique is applied to infer the sound transmission into the impeller. This provides input data for further models to be defined, addressing the question of upstream sound propagation along the inter-blade channels towards the inlet. The matching equations are solved using direct matrix inversion. Preliminary results are given for the reflection and transmission coefficients, both in the absence of flow and including the effect of a purely radial flow.