Experimental Investigation of Unsteady Aerodynamics and Aeroacoustics of a Thin Airfoil

Abstract

An experimental investigation of the unsteady problem for a thin, symmetric airfoil exposed to periodic gusting was performed in a free-jet anechoic wind-tunnel fadlity. The gusting events were created upstream such that there was a small longitudinal, i.e., spanwise, wave number and the gust could be approximated as two dimensional. Measurements of the unsteady velocity field, the unsteady pressure at the airfoil surface, and the acoustic field were made for two values of axial and normal reduced frequency. The unsteady pressure distribution along the airfoil was computed using the Sears method and unsteady velocity data. In addition, the pressure distribution was computed using acoustic data as input to a numerical inversion technique. The results of each technique were compared with the experimentally obtained unsteady pressure distribution. The inversion technique showed good agreement with the Sears method. However, comparison with experimental results illustrated that the theoretical estimates, although exhibiting trends similar to the experimental data, consistently underestimated the experimental unsteady pressure distribution at the lower reduced frequency, indicating the presence of viscous effects. Better agreement between experimental and theoretical results was obtained at the higher reduced frequency where viscous effects were less prominent.