Acoustic Characterisation of Subsonic and Supersonic Elliptical Jets

This work focuses on the experimental characterisation of the acoustic field of an aspect-ratio-two elliptical jet, with comparison to the baseline axisymmetric jet. Measurements are taken at various azimuthal and polar observer angles across both the subsonic and supersonic regimes and are supplemented by particle-image-velocimetry measurements to link the hydrodynamic field to the acoustics. The subsonic elliptical jet almost exactly matches the acoustic field of the axisymmetric jet, while the supersonic elliptical jet displays signs of non-axisymmetric azimuthal directivity in both the screech tone and broadband spectrum. The hydrodynamics suggest that structures involved in driving the screech tone affects its azimuthal directivity across all measured polar angles considered, whereas axis-switching may be associated with the reversed azimuthal directivity of the broadband spectrum downstream of the jet exit.