Broadband shock-associated noise modelling for high-area-ratio under-expanded jets

Broadband shock-associated noise (BBSAN) is an important component of supersonic jet noise for jets at off-design conditions when the pressure at the nozzle exit is different from the ambient. Two high-area-ratio under-expanded supersonic jets at nozzle pressure ratios (NPRs) 3.4 and 4.2 are considered. The jets correspond to conditions of the experiment in the Laboratory for Turbulence Research in Aerospace and Combustion (LTRAC) in the Supersonic Jet Facility of Monash University. Flow solutions are obtained by the large eddy simulation (LES) and Reynolds averaged Navier-Stokes (RANS) methods. The solutions are validated against the particle image velocimetry (PIV) data. For noise spectra predictions, the LES solution is combined with the time-domain Ffowcs Williams-Hawkings method. To probe the accuracy of the reduced-order method based on acoustic analogy, the RANS solutions are substituted in the Morris and Miller BBSAN method, where different options for modelling of the acoustic correlation scales are investigated. The noise spectra predictions are compared with the experimental data from the non-anechoic LTRAC facility and the NASA empirical sJet model. Apart from the low frequencies influenced by the jet mixing noise, the RANS-based acoustic predictions align with those from LES for most frequencies in the range of Strouhal numbers (St) 0.4 < St < 2 within 1-2 dB.