Experiments on installed jet noise

Abstract

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper reports experimental aeroacoustic results on subsonic installed jet obtained in an anechoic facility under isothermal condition for 0.4 ≤ Mj ≤ 0.9 Mach number range in order to extend the knowledge of jet/plate acoustics. A flat plate is employed to mimic a flap (or wing) and the acoustic measurements were performed with an azimuthal microphones array sweeping the 20 deg ≤ θ ≤ 95 deg polar range, and the microphones positioned at a radius of R/D = 14.3. The studied parametric space includes 0.5 ≤ r/D ≤ 1.5 radial distance between the flat plate trailing-edge and the jet axis, L/D = 2 and 3 streamwise distances between the flat plate trailing-edge and nozzle lip and 0 deg ≤ α ≤ 45 deg flat plate incidence angles. Overall, three different spectral signatures were identified for the installed jet noise: broadband, weak (linear) tones and strong (non-linear) tones. The regime of strong amplitude level harmonic (non-linear) peaks was detected in the noise spectra for the 0.5 ≤ r/D ≤ 0.6 radial position for Mj ≥ 0.7. Weak amplitude level tones were identified in the 0.5 ≤ r/D ≤ 0.9 for Mj ≥ 0.6 and only broadband noise was observed for r/D > 0.9. For radial positions r/D < 0.9 and Mj < 0.6, as well as for r/D ≥ 1 and all studied Mach numbers, the installation noise is essentially of broadband nature. A transition regime, in which it is not possible to verify if the weak peaks are present or not, was also identified for some plate configurations (r/D > 0.6) and Mach numbers (Mj ≤ 0.6). The stronger peaks were measured for the r/D = 0.5, L/D = 3 and α = 45 deg configuration, with spectral levels up to 145 dB/St at the polar angle θ = 90 deg.