N142-099 TITLE: Tactical Airplane Noise Reduction via Advanced Automated Computational Airframe Aft-End Integration Technologies

TECHNOLOGY AREAS: Air Platform

ACQUISITION PROGRAM: JSF-Prop

OBJECTIVE: Demonstrate and validate noise reduction capability associated with automated shaping of tactical airplane/engine nozzle interface region to increase near-field mixing.

DESCRIPTION: Noise generated by military exhaust systems presents a community noise problem and becomes a target identifier during strike operations. Exhaust-system acoustic calculations typically assume constant ambient velocity conditions and thus do not capture potential impacts on the nozzle exit-plane flow field due to the local airframe geometry. Furthermore, the bulk of engine acoustics testing is performed with uninstalled engines, either with or without external airflow. Airframe aerodynamic design typically incorporates a low-to-moderate fidelity exhaust plume for thrust/drag computations, with emphasis on cruise conditions where drag/range is the dominant concern for key performance parameters KPPs. The engine/airframe design/testing process does not take advantage of mixing benefits achievable with airframe/nozzle/plume acoustics concurrent design. Although pre-production ground/flight testing does capture the resultant system acoustics level, such testing occurs when the design is extremely difficult to modify.

Recent high-fidelity computational fluid dynamics (CFD) calculations of current state-of-the-art tactical aircraft/nozzle systems at operational conditions and power settings show a substantial increase in plume mixing in the nozzle near-field due to certain airframe features that locally increase exit-plane shear effects. This suggests that consideration of airframe/exhaust geometry modifications for next generation tactical aircraft may be able to magnify such shear mixing to reduce acoustic levels at noise-critical operational conditions and power settings.

The development and demonstration of a computational technology and methodology tool for the concurrent automated shaping of aft airframe and nozzle geometries to reduce tactical aircraft jet noise more than 3dB without any performance penalties (e.g., drag, thrust) is desired. The proposed technologies should inherently capture airplane performance, operability and acoustics effects into an automated optimization framework with high-fidelity CFD and acoustics tools. Generic airframe and generic engine parameters are adequate for this stage of development, as a successful product should easily be configurable to a current naval platform in future efforts.

PHASE I: Demonstrate feasibility that the developed concept can produce a new design for a legacy tactical aircraft/nozzle configuration that results in reduced noise levels (>3dBs) for two points in the mission envelope without adversely impacting critical aerodynamic performance parameters at other key points. Develop a scale-model test plan for validation of the design space.

PHASE II: Conduct the test plan developed in Phase I and compare data to predictions. From this comparison, identify two airframe/exhaust design modifications that meet or exceed current critical performance parameters (noise reduction >3dBs with no change in aircraft performance). Apply this geometry optimization methodology to a selected non-axisymmetric vehicle/exhaust concept to generalize those features and dimensions that can be exploited for noise reduction.

Include data/prediction comparisons to validate the levels of noise reduction resulting from the design process; and parametric plots showing the key geometric features and dimensions for which high levels of noise control can be achieved, for both axisymmetric and non-axisymmetric representative configurations.

PHASE III: Transition to Navy aircraft applications for improved exhaust and aft airframe integration for reduced noise environmental impact. Applications considered should include growth versions of legacy F18 and F35 systems as well as future tactical concept vehicles. In addition, the developed concepts may transition to commercial airliner designs as they have direct application to wing, nacelle, struts and landing gear integration with the gas turbine engine powerplants of those transports for reduced noise environmental impact.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Developed technologies will also be directly applicable to commercial air transports noise reduction.

REFERENCES:
1. Martens, S. and Spyropoulos, J. T., June 14-18, 2010, Practical Jet Noise Reduction for Tactical Aircraft, GT2010-23699, 2010 ASME/IGTI Turbo Expo, Glasgow, U.K.

2. Nichols, J.W, Lele, S.K., Ham, F.E., Martens, S. and Spyropoulos, J.T., 2013, Crackle Noise in Heated Supersonic Jets, Journal of Engineering for Gas Turbines and Power, Vol. 135, pp. 051202-1.

KEYWORDS: Tactical Aircraft Acoustics; Noise Reduction Technologies, Aircraft Aft-End integration, Aircraft Optimization, Nozzle Integration, Large Eddy Simulation (LES)

** TOPIC AUTHOR (TPOC) **

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