Aeroacoustic modal analysis of underexpanded pipe jets with and without an upstream cavity

The investigation of the aeroacoustics of an underexpanded pipe-cavity jet is carried out experimentally. Two different aspect ratios of the cavity are tested for a wide range of nozzle pressure ratios. Both internal and externally radiated pipe-cavity acoustics are studied. Linear and higher-order spectral analyses are implemented on the unsteady cavity pressure to comprehend the nature of the cavity acoustics and nonlinear interactions of different acoustic modes of the pipe-cavity system. Results show that an increase in depth leads to an enhancement in the nonlinear interactions. Furthermore, the power spectral and overall sound pressure level analyses of pipe and pipe-cavity jet noise radiation are carried out. High-speed schlieren imaging techniques are used to understand jet dynamics. Highly unsteady motion of the jet initial shear layer is observed due to an upstream disturbance of the cavity. In addition, proper orthogonal and dynamic mode decomposition methods are used to extract the spatial and dynamic modes of the jet structure. These methods are used to segregate the cavity associated jet dynamics and screech dynamics.

Automated summary

Experimental investigation of the aeroacoustics of an underexpanded pipe-cavity jet was conducted with different aspect ratios of the cavity and a wide range of nozzle pressure ratios. The study focused on both internal and externally radiated pipe-cavity acoustics, showing that increased cavity depth leads to enhanced nonlinear interactions. High-speed schlieren imaging and decomposition methods were used to understand jet dynamics and segregate different dynamics in the system.