A numerical study on the propagation of sound through capillary tubes with mean flow

As a first step toward the acoustic analysis of catalytic converters in automotive exhaust systems, wave propagation through a capillary tube with steady flow is dealt with. Using the general formulations of conservation equations with non-isentropic conditions based on the low reduced frequency solution, the linearised governing equations are solved by the recursive use of numerical methods. No initial assumptions are imposed on the shape of axial velocity profiles and the radial velocity fluctuation is also included in the analysis. Characteristics of the forward and backward propagating acoustic waves are investigated under the influence of steady flow and the calculation is performed up to high shear wave numbers. The characteristics of hydrodynamic waves are also investigated when steady flow is present. The application limits of the previous work are demonstrated as the shear wave number increases. The numerical method is applied to the prediction of the transmission loss of a stack of capillary tubes with and without mean flow considering the effects of radial components and the calculated results agree reasonably well with experimental ones. (C) 1996 Academic Press Limited