The application of a boundary integral equation method to the prediction of ducted fan engine noise

The prediction of ducted fan engine noise using a boundary integral equatio n method (BIEM) is considered. Governing equations for the BIEM are based o n linearized acoustics and describe the scattering of incident sound by a t hin, finite-length cylindrical duct in the presence of a uniform axial infl ow. A classical boundary value problem (BVP) is derived that includes an ax isymmetric, locally reacting liner on the duct interior. Using potential th eory, the BVP is recast as a system of hypersingular boundary integral equa tions with subsidiary conditions. We describe the integral equation derivat ion and solution procedure in detail. The development of the computationall y efficient ducted fan noise prediction program TBIEM3D, which implements t he BIEM, and its utility in conducting parametric noise reduction studies a re discussed. Unlike prediction methods based on spinning mode eigenfunctio n expansions, the BIEM does not require the decomposition of the interior a coustic field into its radial and axial components which, for the liner cas e, avoids the solution of a difficult complex eigenvalue problem. Numerical spectral studies are presented to illustrate the nexus between the eigenfu nction expansion representation and BIEM results. We demonstrate BIEM liner capability by examining radiation patterns for several cases of practical interest. (C) 1999 Academic Press.