TECHNOLOGY AREAS: Air Platform, Weapons

OBJECTIVE: Define new approaches to the design and performance analysis of nozzle components that attenuate the exhaust jet noise of the powerplants of modern tactical aircraft. Analysis may be done by current state-of-the-art computational fluid dynamics (CFD) modeling and simulation methodologies.

DESCRIPTION: The noise from the turbulent, hot, supersonic jets at take-offs and landings as well as high-Mach cruise at altitude dominates noise emanating from other powerplant components (e.g., fan, combustor) and has significant safety implications for launch personnel as well as environmental impacts of noise pollution around military installation. Noise generation mechanisms of supersonic jets are quite complex and different than those of subsonic jets typically encountered in the exhausts of high-bypass ratio transport aircraft powerplants. Both subsonic and supersonic jets contain small and large-scale turbulence structures. While small-scale turbulence structures are the dominant mechanism of subsonic jets, the large-scale turbulence structures are dominant in supersonic jets. Intense Eddy Mach wave radiation from regions along the jet shear layer is produced by the large-scale turbulence structures convected supersonically relative to the ambient medium. Additionally, oblique shock cell quasi-periodic structures, the result of imperfectly expanded supersonic jets, are noise radiation sources and contribute to discrete tone screech and broadband frequency noise.

New innovative approaches are sought to aid in the design and engineering of nozzle components that attenuate the exhaust jet noise of the low-bypass ratio powerplants of modern tactical aircraft. New, quieter nozzles should be optimized for performance at take-offs and landings as well as at high-Mach cruise at altitude. Furthermore, efficient integration of the nozzles with airframe is also critical since forward flight modifies exhaust jet noise and the optimization of the quiet nozzle designs needs to be achieved both at the component and system level.

Critical to this effort is the improved prediction and understanding of the turbulent mixing of hot supersonic jets under pressure-matched and pressure-mismatched conditions -- which is central to improving aeroacoustic predictions of these propulsive jet flows. This breaks down to the developement of Large Eddy Simulations of hot supersonic jets issuing from propulsive nozzles, improved modeling of shock-containing jet plumes, and physics-based noise predictions for these flows which include both jet mixing noise and the shock-associated noise..

PHASE I: Demonstrate the feasibility of proposed methodologies for nozzle performance analysis on mutually-agreed government-furnished test case(s). Of primary interest is the accuracy of the methodologies compared to full scale experimental data. Of secondary interest is the practicality of simulations in terms of turn-around times and computer resources required for the simulations. Applicability of these methodologies in the design process for nozzles for tactical aircraft will also need to be demonstrated.

PHASE II: Develop design procedures employing Phase I methodologies. Further improve selected methodologies so that they can be employed/validated in ongoing DoD programs. Demonstrate accurate performance analysis of proposed nozzle concepts with quick turn-around times.

PHASE III: Transition the technology to ongoing DoD programs. Demonstrate that the transition of this innovation leads to significant cost savings in the design of nozzle components for tactical aircraft by major powerplant DoD contractors.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Innovative modeling and simulation tools for aero acoustics are necessary in the design of advanced quiet nozzles for High-Speed Civil Transports (HSCT) and Supersonic Business Jets (SBJ). The successful development of technologies in this program will address jet noise, a major hurdle in the development of these next generation commercial aircraft, and will offer solutions to the newly emerging large by-pass area ratio gas turbine engines being deployed on the latest civil transport designs. Jet noise reduction will offer increase flexibility in domestic flight paths and airport locations by reducing the noise footprint typically produced by high speed aircraft.

REFERENCES:
1. AGARD Conference Proceedings 512, "Combat Aircraft Noise," AGARD CP-512, April 1992. (and references therein)

2. Tam, Christopher K.W., "Supersonic Jet Noise," Ann. Rev. Fluid Mech., Vol. 27, 1995, pp. 17-43.

3. Colonius, T. and Lele, S. Kl, "Computational Aeroacoustics: Progress on Nonlinear Problems of Sound Generation," Elsevier Progress in Scientific Sciences, Vol. 40, 2004, pp. 345-416.

4. Reba, R., Narayanan, S., Cololius, T., and Dunlop, M. J., "A Study of the Role of Organized Structures in Jet Noise Generation," AIAA Paper 2003-3314.

KEYWORDS: Nozzles; Supersonic Jet; Exhaust Jet Noise; Propulsion/Airframe Integration; Tactical Air Vehicle; Computational Fluid Dynamics; Large Eddy Simulation