Study of the acoustic oscillations by flows over cavities. Part 2. Sound reduction

Abstract : We present experimental results obtained with a deep cavity, like an Helmholtz resonator, excited by an airflow. The resonance under the action of the vortices generated in the shear layer is well described and quantified. The mounting of actuators, based on a few piezo-electric elements, allows to generate a series of two-dimensional vortices forced at a frequency which is different than the natural resonance frequency. The sound level in the cavity is strongly decreased and the broadband noise of the turbulence only remains.