N102-128 TITLE: Predictions of the Acoustic Nearfield on a Carrier Deck

TECHNOLOGY AREAS: Air Platform, Information Systems, Sensors

ACQUISITION PROGRAM: Joint Strike Fighter Program

OBJECTIVE: Develop a practical approach to defining the noise radiating properties of a supersonic jet so that it may be used as an equivalent source in commercial Boundary Element Analysis (BEA); Finite Element Analysis (FEA); or Statistical Energy Analysis (SEA) noise prediction models.

DESCRIPTION: Modern propulsive supersonic jets produce a high amplitude noise field with complicated characteristics. The apparent noise source as measured and mapped using acoustic holography methods occurs from 1 to 100 nozzle diameters behind the engine due to a variety of turbulent behaviors of the hot jet. This complicated aeroacoustic problem is not easily modeled using classical analytical approaches. The key difficulty addressed in this work is characterizing the source. Turbulent, hot supersonic jets have been shown to radiate noise with "beaming" in certain directions. This is different than a "simple source" which typically radiates with spherical spreading. In a supersonic jet, turbulent eddies with some favored dimensions are translating at high speed along the jet boundary, in the shear layer, and produce frequency and direction dependent noise. It is desired to develop procedures to characterize or approximate this noise source in a way that would allow use of commercially available noise modeling methods (such as BEA, SEA or similar).

The candidate approach should be capable of working from government provided reference measurements of the sound "nearfield" close in around a supersonic jet, and produce a source, or forcing definition compatible with a commercial noise modeling code. The noise code, using the provided source definition must then predict the frequency and angle dependent noise field out to all practical distances. Methodologies should demonstrate the ability to account for superposition of the jet noise fields from multiple jets during simulated high activity carrier launch and retrieval operations, as well as the noise reflecting characteristics of the aircraft, jet blast deflectors and other carrier deck features. The developed approach will be evaluated by applying the method to a sample of measured nearfield jet noise data and give a reasonably accurate blind prediction of the noise as measured anywhere in the region.

Of primary interest is the accuracy of the methodologies compared to measurements to predict noise at particular crew locations in the noise field. Of secondary interest is the practicality of simulations in terms of turn-around time, complexity of needed data and computer resources required for the simulations.

PHASE I: Develop, demonstrate and prove feasibility of a procedure to process measured nearfield noise data from a supersonic jet in order to create source inputs to commercially available nose modeling methods that will be capable of predicting both near and far field noise.

PHASE II: Extend the method developed under Phase I to include the effects of typical features of an aircraft carrier deck, such as a Jet Blast Deflector (JBD) and superposition of multiple jet streams. Develop a prototype procedure/methodology and demonstrate the accuracy and practicality of the prototype.

PHASE III: Finalize into a practical procedure and transition methodology to US Navy and potential commercial customers.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Extension of one or more commercially available noise prediction tool to model supersonic flow as a source may allow such tools to be applied in a variety of other situations. Supersonic business jets are being contemplated by some manufacturers. Further, such methods may allow community noise predictions due to aircraft operations that would be generally useful.

REFERENCES:
1. Ikelheimer, B. J. (2005). Advanced simulation noise model for modern fighter Aircraft. Proceedings of Noise-Con 05, Minneapolis, MN

2. Gee, K. L. (2005). Prediction of nonlinear jet noise propagation (Doctoral thesis). The Pennsylvania State University.

3. Simonich, J.C., Schlinker, R.H., (2008) Measurement of Source-Wave Packets in High Speed Jets and Connection to Far Field, AIAA 2008-2891.

4. Reba, R., et al, (2005). Modeling Jet Noise from Organized Structures Using Near Field Hydrodynamic Pressure, AIAA 2005-3093.

KEYWORDS: aeroacoustics; jet noise modeling; noise prediction; supersonic jet noise; boundary element analysis; statistical energy analysis

** TOPIC AUTHOR (TPOC) **

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