Aerodynamic noise from a poroelastic edge with implications for the silent flight of owls

The interaction of a turbulent eddy with a semi-infinite poroelastic edge is examined with respect to the effects of both elasticity and porosity on the efficiency of aerodynamic noise generation. The scattering problem is solved using the Wiener-Hopf technique to identify the scaling dependence of the resulting aerodynamic noise on plate and flow properties, including the dependence on a characteristic flow velocity U. Special attention is paid to the limiting cases of porous-rigid and impermeable-elastic plate conditions. Asymptotic analysis of these special cases reveals parametric limits where the far-field acoustic power scales like U-6 for a porous edge, and a new finite range of U-7 behaviour is found for an elastic edge, to be compared with the well-known U-5 dependence for a rigid impermeable edge. Further numerical results attempt to address how trailing-edge noise may be mitigated by porosity and flexibility and seek to deepen the understanding of how owls hunt in acoustic stealth.