Prediction of noise induced by low mach number flows using a hybrid CFD/BEM approach

A hybrid CFD/BEM approach is proposed to extract the acoustic sources generated by low Mach number flow past a circular cylinder and to predict the associated far-field acoustic pressure. An incompressible computational fluid dynamics (CFD) solver is used to calculate the transient hydrodynamic flow field. Acoustic sources based on the linearised perturbed compressible equations (LPCE) are then extracted from the flow field data and combined with a boundary element method (BEM) model of a rigid circular cylinder to predict the sound pressure field. The spatial resolution of the extracted acoustic sources from an acoustic perspective is much finer than required, which may lead to inefficiencies in the BEM analysis. In this work, a method is developed to spatially condense the acoustic sources extracted from the CFD data to reduce the number of acoustic sources, while preserving the accuracy of the predicted sound pressure field. The results from this hybrid CFD/BEM approach are presented for flow past a circular cylinder with Reynolds number, ReD=100 and Mach number, M=0.15. The directivity of the radiated sound pressure field at the vortex shedding frequency agrees well with results of alternate methods available in the literature. The spatial condensation method is shown to produce good accuracy provided the particle spacing is sufficient to preserve the phase relationship between nearby acoustic sources.