Acoustic Resonance in an Annular Cavity with Axial Transit Flow

The results of a consistent computational and experimental study of acoustic self-oscillations in an annular cavity surrounding a circular pipe with a local narrowing are given. In the experiment, pressure fluctuations were measured on the outer wall of the annular cavity for various volume flow rates; air entered the pipe at the atmospheric pressure. It was found that the flow regime with excitation of acoustic self-oscillations in the cavity is implemented in a certain range of flow rates. The oscillation frequency corresponds to the first natural frequency, and the root-mean-square values of pressure fluctuations reach a level of 2300 Pa. Numerical simulation based on the RANS approach, carried out for the geometry and conditions of experiment, reproduces the observed effect of acoustic excitation of the cavity and gives similar values of the fluctuation amplitude. The oscillation modes developed at various volumetric flow rates are analyzed based on the obtained calculated data.