Determination of the Far Field Sound Radiation from Flames Using the Dual Reciprocity Boundary Element Method

Abstract

The present work addresses the calculation of the radiated sound power spectrum in the far field of open or enclosed flames based on the application of the dual reciprocity boundary element method (DRBEM). The focus of this work is the development of a technique that allows a good representation of the sound field, assuming that the sound sources originated by the combustion are known. Following the acoustic analogy approach, the sound radiation of open flames can be evaluated by a volume integral over the equivalent acoustic source terms in the combustion zone. The DRBEM allows replacing the volume integral by a series of surface integrals. The technique is applied to the theoretical model of a spherical flame. The accuracy of the DRBEM model can be studied by comparing it with available analytical solutions for the sound radiation of this flame type. For enclosed flames, the DRBEM is used to calculate the sound propagation in the region of temperature gradients that appears at the exhaust of the combustion chamber. The sensitivity of the radiated sound field to this adjacent inhomogeneous temperature field is investigated. The non-uniqueness problem of the boundary integral equation method is tackled by the Burton and Miller approach. The DRBEM allows an effective determination of the radiated acoustic field because it can take into account inhomogeneities and satisfies automatically the radiation condition at infinity.