The very high noise levels generated by high performance, supersonic military aircraft is a safety concern to those working around the engine exhaust. As the Department of Defense (DoD) operates new aircraft with increasing jet engine thrust, the noise impact gets worse and there continues to be a strong need for military jet noise reduction. This project will rapidly and substantially mature several promising and practical jet noise reduction concepts to develop noise reduction technologies that can achieve noise reduction up to 5dB and are retrofittable to the existing F404 engine with potential of transition to other engines/platforms. The project will include two major components:
- Assess three promising noise reduction concepts using both numerical and scale-model experimental approaches. Explore the optimal noise reduction configuration for each concept on scale-model military engine nozzles.
- Assess the 2-3 most promising noise reduction configurations in full-scale engine tests to confirm their performance and assess their impact on thrust.
The project will mature and refine new jet noise reduction concepts that demonstrated substantial noise reduction in the laboratory. The Naval Research Laboratory (NRL) physics-accurate Large Eddy Simulation (LES) tool JENRE will be used to run numerous high-fidelity fluid flow simulations of full-scale nozzle modifications on DoD high-performance computing (HPC) resources. This approach is not currently utilized by industry in developing designs for practical jet engines. However, this effort will result in far more accurate predictions of jet turbulence, and the resulting jet noise than the Reynolds Averaged Navier Stokes (RANS) or Unsteady RANS (URANS) approaches used by industry as the current state of the art. A joint effort will be conducted to experimentally optimize and refine several new noise reduction concepts with application to a GE F404 nozzle. Finally, the investigators will settle on the top two or three passive noise reduction concepts for further maturation. A set of full scale / production F404 nozzle seals will be modified to implement each concept. Then a series of uninstalled GE F404 engine noise measurements will be performed in order to confirm or deny the predicted noise reduction at full scale. This multi-level approach is expected to rapidly mature up to three new concepts, each of which have been shown to be effective and promising in preliminary laboratory testing.
This effort will result in the rapid maturation from below technology readiness level (TRL) 4 to at least TRL 5 of several promising passive jet noise reduction technologies. The project focuses on those concepts that are potentially applicable to retrofit on legacy DoN supersonic aircraft engines. The joint effort between the modern full-physics LES tools and laboratory-scale tests to screen, optimize and confirm the effectiveness of these approaches in more realistic conditions ensures a high likelihood of success. The final evaluation at full scale, on an engine at realistic operating conditions, will confirm a jump to TRL5+. This rapid maturation timetable has the potential to save substantial DoD resources and allow transition to the fleet far faster than any other approach. The concepts being considered include: A) nozzle seal mounted micro vortex generators, B) TRL 6 proven chevron nozzle seals, modified to vary azimuthally so as to focus noise reduction below and to the sides, while reducing thrust impact, and C) sweeping jet actuators. They are easy to retrofit in an existing engine and have a relatively high likelihood of providing substantial improvement over the current state of the art chevrons solution.