LES-based evaluation of a micro-jet noise reduction concept in static and flight conditions

The Large-Eddy Simulation (LES) numerical system for jet noise computation established since 2002 is used to explore the relatively new noise-reduction concept (injection of high-pressure micro-jets in the vicinity of the main jet nozzle exit). Simulations performed not only demonstrate a capability of the system to capture the essential features of the flow, turbulence, and the far-field noise alteration caused by the micro-jets, but also to reveal the subtle flow features responsible for the effect of injection on noise. Results obtained are in line with the conclusions of experimental studies regarding efficiency of the micro-jets injection in static conditions and, in particular, suggest that this results in a noise reduction comparable with that from chevrons in the lowfrequency range and in a less pronounced high-frequency penalty. However this advantage of the micro-jets noise-reduction concept is mitigated by results of simulations in flight conditions, for which no experimental data are available. This conclusion makes a practical use of the concept for noise reduction of the aviation engine exhaust jets rather unlikely.