Measurements of subsonic elliptical jets and their sound

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© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper reports acoustic and velocity-field measurements on subsonic elliptical jets of 1:2 aspect ratio and Dh = 50 mm nozzle hydraulic diameter. The experiments were performed in the 0.4 to 0.9 Mach number (Mj) range, and all tests were conducted in an anechoic facility. Acoustic power spectral density (PSD) results were obtained with an antenna containing 18 azimuthally distributed microphones at a radius R/Dh = 14.3, and for polar angles in the 20 deg ≤_θ≤ 95 deg range. We show that the acoustic field of the 1:2 aspect ratio elliptical nozzle is very similar to the (axisymmetric) round nozzle acoustic field measurements, even for θ = 90 deg, i.e. the position closest to the nozzle exit. The spectra of both nozzles, round and elliptical, have approximately the same signature, i.e. broadband, and noise intensity levels. Stereo particle image velocimetry (stereo PIV) measurements enabled the assessment of the three velocity components for a series of cross-flow planes up to the streamwise distance x/Dh = 15 (750 mm). Such measurements were conducted only for Mj = 0.4 and 0.7. The results show that at least up to x/Dh = 3, the jet flow field keeps a proper elliptical profile, including a well-defined shear-layer. Far downstream, e.g. x/Dh = 8, it is observed a merging of the shear-layer with the jet core flow and, regarding mean flow and root-mean-square (rms) metrics, the developed flow field becomes approximately round.