Aeroacoustic characteristics of subsonic flow from axisymmetric pipe-cavities

A detailed experimental study on the acoustic characteristics of an axisymmetric pipe-cavity jet is conducted for different ratios of cavity depth to length, over a range of subsonic Mach numbers. Power spectral analysis and Scalogram are implemented to unravel the physics of the pipe-cavity resonance. Proper Orthogonal Decomposition analysis is used to understand the flow dynamics of the pipe-cavity jet. The results show that the pipe-cavity resonates close to the first tangential mode for a wide range of Mach numbers. However, an increase in the depth and Mach number leads to the onset of combined resonance modes. Experimentally obtained resonance frequencies are validated against numerical simulations and theoretical predictions. Scalogram results show the existence of nonlinear interactions and mode shifting of resonance modes. A parametric space plot demarcates the domains of operation of various oscillation modes, over the relevant parametric range. The results reveal that the upstream cavity significantly affects the downstream jet flow dynamics, and its far-field noise radiation. Deeper cavities have a stronger influence on the far-field acoustics compared to shallow cavities.