Properties of bulk reacting absorbers subject to flow and temperature boundary layers S. Boij, R. Glav KTH - Royal Institute of Technology, MWL and Centre for ECO2 Vehicle Design A. Färm Scania CV AB, Södertälje, Background Automotive applications Noise encapsulations 50 ≤ f ≤ 5000 Hz Grazing flow Mach no. < 0.2 2 Background Complex sound and flow field R,α Sound Flow Sound Heat Flow Vibrations Noise encapsulation Low Mach numbers Bulk reacting liners Strong temperature gradients Surfaces close to source Problem Generic case – plane wave incidence Bulk reaction Local reaction Absorber modelling – bulk reaction Equivalent fluid model •  Transfer Matrix Method, TMM 𝑇 Rigid backing, v =0 0 Boundary layer modelling Discretizing the boundary layer with TMM M z δ d d M i x Boundary layer modelling Discretization with gradients •  Extension of original TMM M(z) z δ d d z n x