Experimental investigation of a cylindrical cavity in a low Mach number flow

The aeroacoustics of a cylindrical cavity with aspect ratio (Depth/Diameter) 1.357 is investigated through experimental measurements conducted in a low speed recirculating wind tunnel. The aim of the study is to characterize the velocity field outside of the cavity and to determine the major acoustic modes influencing both the velocity and the wall pressure statistics. Aerodynamic and wall pressure measurements are carried out at different Reynolds numbers using a hot wire anemometer and wall mounted microphones. The reattachment region of the shear layer and the presence of the vortices in the wake region are identified. Pressure and velocity Fourier spectra evidenced the presence of three resonance modes at frequencies well predicted by classical theoretical formulations developed in literature for rectangular cavities. Results obtained through a Finite Element (FE) simulation are in agreement with the measured lock-on frequencies. The effect of the flow structures upon the wall pressure statistics is evaluated by wall pressure measurements conducted in several positions over the cavity. By a separation of the wall pressure spectra into specific frequency bands, the nature (acoustic or hydrodynamic) of the dominant modes is identified. An overall description of the flow physics inside the cavity is proposed.