Impedance boundary condition in frequency domain DG code for modelling liner effects in complicated intake ducts.

An impedance problem is fundamental to computing acoustic wave propagation. Here, the focus is on applying an impedance boundary condition derived from first principles for modelling a realistic acoustic liner. Simulations are performed in frequency domain where the Acoustic Perturbation Equations (APE) are solved with Discontinuous Galerkin (DG) method. In order to achieve a physical boundary layer - surface interaction, the APE propagation equations are solved on top of a wall-resolved RANS flow that is obtained from a precursor CFD simulation. Key findings include the analysis of a flux balance across the impedance boundary. Also, the method is applied to solve a challenging Unmanned Combat Aerial Vehicle (UCAV) problem with acoustic modes propagating in a complicated intake duct where it is hardly possible to establish an analytical solution. DLR F-24 MULDICON UCAV (MULti-DIsciplinary CONfig) test platform is used for demonstrating a low noise modification by inclusion of impedance boundary of a realistic size which is conveniently integrated into the duct for the ease of liner manufacture and service