7. Conclusions
In this paper, a methodology is presented which couples the The WEM with the Myers flow impedance boundary condition in order to examine acoustic propagation through a lined duct with flow. The Myers boundary condition has been implemented for the first time in the WEM by explicitly evaluating the derivatives of the base plane-wave functions and augmenting the local stiffness values accordingly. The computed reduction in SPL across the NASA GIT configuration agrees well with the measured data in terms of both SPL and phase across the liner. Deviations in this agreement have been accounted for. The method has been used to educe impedance values, which are consistent with those determined using alternative, often more demanding, approaches. Analysis of the reflection coefficient shows that the Myers boundary condition fails to fully model the wave behaviour across the liner at low frequencies. Aside from this, the discretisation scheme itself has been shown to be considerably more efficient than a comparable FEM discretisation. The WEM with the Myers boundary condition offers a highly efficient numerical methodology for computing acoustic propagation in lined ducts with a grazing flow