Towards Noise Mitigation in Twin Supersonic Rectangular Jets: Baseline Large-Eddy Simulation and Validation

The intense acoustic emission due to supersonic jets is detrimental to carrier flight deck personnel health, nearby communities, and the aircraft structure itself, and is a problem that is exacerbated in multijet configurations. In conjunction with experimental efforts, high-fidelity large-eddy simulations (LES) of supersonic twin rectangular jets issuing from aspect ratio 2:1 nozzles at a nozzle pressure ratio (NPR) of 3.0 are conducted and validated towards the characterization of the noise-generation mechanisms involved in supersonic jets, particularly those relevant to jet-to-jet coupling. Efforts towards ascertaining the sensitivity of the acoustic predictions to the grid design is described. In addition to the usual necessity of high levels of mesh resolution to resolve the turbulence-containing regions of the flow, strategies particular to the twin jet problem, namely reducing lateral mesh transitions in the early post-nozzle flow, are also discussed. The LES results are compared to experimental acoustic measurements and available flow visualizations. Using the established baseline grid design, preliminary data analysis is conducted to ascertain the twin jet coupling and screech dynamics reproduced by the LES. Time-frequency analysis and spectral proper orthogonal decomposition (SPOD) reveal that the LES twin jet flow exhibits screech intermittency, and educes their anti-symmetric coupling. The present LES setup represents a first step towards establishing a baseline to which upcoming simulation/experimental runs with fluidic injection can be compared, and the mechanisms of resulting phenomena analyzed.