An experimental investigation of trailing-edge noise reduction due to elasticity

The proximity of the source and an edge can make the acoustic scattering by wings a significant source of aerodynamic sound. Theoretical results have shown that elastic edges lead to reductions of acoustic scattering; however, experimental confirmation of theoretical trends is difficult, since surface vibrations modify both the source structure and the scattering properties. A simplified, controlled setting for measurements of acoustic scattering, allowing the evaluation of fluid-structure interactions, would thus be desirable to study how elastic edges modify the radiated sound. We present an experimental procedure to isolate the scattered field using a loudspeaker in the vicinity of at plates. The methodology is applied to three different plates, made of steel, aluminum and carbon fiber, as a demonstration. The responses of these elastic plates are studied for a sound source of dipole type near the trailing edge. The method is based on the experimental determination of frequency response functions between source and radiated sound for experiments with and without the plate; subtraction of results, accounting for amplitude and phase, isolates the scattered field. Experimental results treated with the developed procedure were compared with predictions made by numerical simulations performed with a Boundary Element Method (BEM), coupling the acoustic problem with the plate vibration. The comparison between experimental and numerical results revealed that a two-dimensional model can predict satisfactorily the reductions in scattered field by elastic plates observed in the experiment. The present methods can be used to support the choice between different materials for edges focusing on their respective acoustic benefit.