Acoustic forcing to simulate the plunging motion of an airfoil

An alternative to performing dynamic plunging measurements on an airfoil is presented, which is suitable for high reduced frequencies. Instead of physically displacing the airfoil, the flow is modulated by loudspeakers. The loudspeakers are tuned to the first transversal eigenfrequency of the wind tunnel, which results in a 2D acoustic field. The paper first describes the experimental investigation of the acoustic field without a main flow. Then results of acoustic field measurements are compared to a commercially available boundary-element method. The results of local pressure measurements on the airfoil are compared to predictions of a numerical solution of the Euler equations for in inviscid compressible flow. This solution includes the acoustic field. A strong point of the method is that the excitation amplitude can be varied easily.