N102-133 TITLE: Aeroacoustics of High-Speed Jet Impingement

TECHNOLOGY AREAS: Air Platform

ACQUISITION PROGRAM: Joint Strike Fighter

OBJECTIVE: Develop an innovative predictive modeling and simulation tool for the complex phenomena associated with the flow-acoustic resonances arising from jet impingement primarily from short and vertical-take-off (STOVL) tactical aircraft.

DESCRIPTION: In short- and vertical-take off configurations of STOVL tactical aircraft the propulsive nozzles are rotated toward the ground to generate the necessary lift. When that happens, the high-speed hot jet from the engine exhaust, as well as cooler jets from the roll-post nozzles on the wings (and possibly from the lift-fan as in the JSF F-35), impinge on the ground plane. These jets are then deflected by the ground and this process creates complex aerodynamic and aeroacoustic interactions (of the jets with themselves as well as with the ground). These interactions depend primarily on the airframe and nozzle geometries as well as the engine operating conditions. Flow-acoustic resonances arise causing significant unsteady structural loading on the airframe surfaces. In addition, the detrimental effect of noise on maintenance and support launch personnel is a health issue. It is also a safety issue because STOVL operations noise significantly reduces the ability of the pilot and support personnel to communicate effectively jeopardizing safety. A similar, but less complex situation, occurs in the Navy-unique application of carrier take offs in front of the Jet Blast Deflector (JBD). Predictive simulations of these complex coupled impinging jet flow phenomena are only possible by a systematic development of large eddy simulation (LES) capabilities or other high-order multi-scale numerical simulation techniques. By having a complete understanding of the flow-generated noise and its effect on personnel, air vehicle performance, and structural integrity, improvements to the design and carrier logistics can be realized. Innovative modeling and simulation tools are sought that can capture these phenomena and provide key solutions to STOVL tactical aircraft engineers.

PHASE I: Determine the feasibility of accurately modeling the aeroacoustics of high-speed jet impingement, taking into account all of the aerodynamics and physical boundaries necessary to capture said phenomena. Show preliminary approach to impacting the design and carrier deck logistics.

PHASE II: Develop prototype model and simulation (M&S) software reproducing scale model results. The M&S tool should provide accurate comparison to key metrics measured from test.

PHASE III: Integrate software into the design practice and mission logistics of VSTOL aircraft operation on carriers.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: JBDs are used in commercial airports to reduce the ground-level sound and propagation of jet noise. The structural fatigue and noise associated with this practice would benefit from a better understanding of the aeroacoustics.

REFERENCES:
1. Krothapalli, A., Rajkuperan, E., Alvi, F. & Lourenco, L., "Flow field noise characteristics of a supersonic impinging jet," J. Fluid Mechanics, 315, 1999, 155-181.

2. Henderson, B., Bridges, J. & Wernet, M., "An experimental study of the oscillatory flow structure of tone-producing supersonic impinging jets," J. Fluid Mechanics, 542, 2005, 115-137.

3. Henderson, B., "The connection between sound production and jet structure of the supersonic impinging jet," J. Acoustical Society America, 111, 2002, 735-747.
4. Alvi, F.S., Ladd, J. A. & Bower, W.W., "Experimental and computational investigation of supersonic impinging jets," J. AIAA, 40, 2002, 599-609.

KEYWORDS: Jet Impingement; Large Eddy Simulation; Jet Blast Deflector; Jet Noise; Aeroacoustics; Exhaust Plume

** TOPIC AUTHOR (TPOC) **

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