Sound generated by an elastic wing actuated at its leading edge

We study the motion and sound of a thin elastic plate actuated at its leading edge by small-Amplitude periodic pitching and heaving, and subject to uniform low-Mach flow. When the frequency of actuation coincides with an eigenfrequency Ωres of the unforced plate, a resonance motion is excited and the plate oscillates at the corresponding eigenmode. The dynamical description is used to formulate the acoustic problem, where the sources of sound include the plate velocity and fluid vorticity. Acoustic radiation of a dipole type is calculated and discussed in the limit where the plate is acoustically compact. It is found that plate elasticity has opposite effects on sound radiation, depending on the forcing frequency: at frequencies close to Ωres, the near-resonance motion results in the generation of high sound levels; however, at frequencies far from Ωres, plate elasticity reduces the amplitude of plate deflection (compared to that of a rigid plate), leading to noise reduction. The results identify the trailing edge noise as the main source of sound, dominating the sound generated by direct plate motion. The analysis is suggested as a preliminary tool for examining the acoustic signature of flapping flight, common in insects and flapping micro-Air-vehicles.