A perturbation equation system will be extended for the simulation of the reduction of airframe noise through the application of flow-permeable materials at high Reynolds numbers. The system is based on volume averaging and uses additional terms to model the small scale structure of the material. The fundamental mechanisms of noise reduction at flow permeable edges in tangentialflow will be explored and rank-ordered. The simulation method will be validated by means of impedance tube experiments, DNS data and new experimental acoustic data of the trailing edge noise of an airfoil.