Fast low-storage method for evaluating lighthill's volume quadrupoles

Anm-multipoleparticle- condensationmethodisproposedtospatiallycondensethevolumetricquadrupolesources based on Lighthill's acousticanalogy that are extracted from computational-fluid-dynamics data. The purpose of the method is to reduce both the amount of data that must be stored during the computational-fluid-dynamics analysis and the number of acoustic sources driving the subsequent acoustic-propagation analysis, while preserving the accuracy of the predicted sound pressure field. The method uses a particle approximation of the quadrupole source distribution and employs a Taylor series expansion of the harmonic Green's function to spatially condense the underlying acoustic sources and preserve their multipole moments. Low-Mach-number flow around rigid-walled stationary bodies in a medium at rest at infinity is used to demonstrate the m-multipole particle-condensation method. The directivity of the sound pressure field due to the quadrupole sources is presented for the first four harmonics of the vortex-shedding frequency for flow past a circular cylinder with Reynolds number Re^D = 100 and Mach number M = 0.02.Using them-multipole particle-condensation method,the number of acoustic sources is reduced by a factor of 120 with the associated far-field sound pressure levels within 0.5 dB of the noncondensed results for all four harmonics.