A mapped, factored-implicit scheme for the computation of duct and far-field acoustics

Abstract

system that is boundary fitted, with grid points that may be concentrated as desired on the boundary for high resolution. Use of such a general mapping procedure, together with an explicit acoustic algorithm, is described by White 3 for the analysis of noise propagation in a two-dimensional, variablearea duct. A second objective is that the algorithm should not require excessive computer memory, but at the same time should provide an accurate approximation of the acoustic field. In order to satisfy these requirements, a transient finite difference method together with a factored-implicit procedure was chosen. Finally, the procedure should allow the noise calculation to proceed for some distance beyond the duct exit so that an appropriate acoustic boundary condition may be specified. This approach should be more accurate than terminating the calculation at the duct exit where only an approximate boundary condition can be specified. Also, information on the noise levels and radiation patterns emanating from the duct exit will be provided. In the sections that follow, the algorithm is briefly described and the numerical results of a test case are presented.