Airfoil noise is a dominant component in the acoustic signature of a wide variety of aerodynamic systems. In line with current interest in reducing aircraft noise, the present work studies means by which airfoil aerodynamic sound may be monitored. The principal approach adopted is motivated by biomimetic observations of the quiet flight of owls. Subsequently, we investigate the effects of airfoil porosity, elasticity and non-homogeneity on the acoustic far field of a two-dimensional airfoil set at low Mach and high Reynolds number flow. Applying the Powell-Howe acoustic analogy, the system near-field description is obtained using thin-airfoil methodology, and then substituted as a source term in the vortex sound equation. The leading order airfoil dipole-type signature is evaluated, and conditions for sound reduction and amplification are found. The limit case of a thin airfoil having vanishing bending rigidity is examined in detail, to rationalize the impact of material flexural stiffness on the system near and far fields.
In a secondary effort, the broad-band aerodynamic noise of a NACA0012 airfoil is investigated using high-fidelity Large Eddy Simulations (LES). The obtained noise sources are projected to the far field using the Ffowcs Williams-Hawkings acoustic analogy. Both near- and far-field results are validated, followed by preliminary investigation of the effects of trailing-edge temperature variations on the system acoustic radiation.