Aeroacoustic Phenomenon in centrifugal compressors

Abstract

Flow unsteadiness caused by impeller rotation, vortex-shedding, secondary flows etc. can lead to the generation of acoustic waves within the turbomachinery cascade. This causes pressure loading on the impeller. When acoustic resonance occurs, i.e. the frequency of acoustic wave excitation matches with the structural natural frequencies of the impeller, high fatigue and vibrations are encountered, which can lead to structural failure. Centrifugal compressor applications like turbocharging and process engineering require an advanced understanding of the aeroacoustic excitation mechanisms as these have been suspected of playing a significant role in structural failures. Given that the current state-of-the-art analysis methods are incapable of explaining various instances of structural failures, a novel Lattice Boltzmann Method (LBM) based approach is explored. For the first time, aerodynamic and performance predictions, along with aeroacoustic amplitudes from the LBM based approach will be compared with a conventional Unsteady Reynolds Averaged Navier Stokes (URANS) based approach as well as test rig data. This will assess the feasibility of the LBM model for analysing forced response behaviour of a centrifugal compressor operating at conditions of acoustic resonance. The research compressor has been chosen based on an aeromechanic test campaign where high impeller blade trailing edge vibrations were measured. The computational domain consists of full compressor wheel including the hub and the shroud cavities. An attempt will be made to quantify the resonant amplification factor by simulating off-resonant conditions. The findings from this research would result in the development of a numerical framework for assessing the physics and severity of resonant excitations in centrifugal compressors. It will also highlight the importance of accounting for aeroacoustic mechanisms in the aeromechanical design of centrifugal compressor stages.