On the connection between near-field and far-field solutions of high-speed jet noise

Recent computational aero-acoustics development for high speed jet noise has focused on advanced LES methods. Validation efforts have largely been directed at comparisons in the acoustic far-field. While these results have shown encouraging levels of agreement, they bypass direct comparison on the basis of jet source characteristics. Thus, the current study aims to compare LES on the basis of multi-point statistics of jet near-field hydrodynamic pressure. A key advantage of the study is the provision for an intermediate check on the "beginning to end" simulation methodology by way of the near field measurements. High-fidelity simulations using improved low dissipation and low dispersion high-order numerical (CFD) schemes were carried out for flows from a round nozzle, with the inclusion of the nozzle in the model. Experimental measurements for the subsonic jet near-field noise assessments were obtained from a prior study led by Bridges at NASA using an array design by Suzuki and Colonius¹⁹ with jet flows corresponding to test cases reported by Tanna¹. Supersonic shock free near field jet noise measurements were acquired at UTRC using a novel rotating phased array system reported here for the first time. The simulated near-field results were generated directly from the RANS/LES calculations, whereas the far-field results follow from the Ffowcs Williams-Hawkings (FW-H) projection of the near-field results. Our results have shown a consistent over-prediction of the jet spreading rate. Despite this, salient qualitative features of the near-field source characteristics are captured in the simulations. Detailed analysis and resolution of the sources of discrepancy are currently in progress.