Center for Aerospace Acoustics

Christopher Fuller, Ph.D.

The Center for Aerospace Acoustics at the National Institute of Aerospace was founded to explore acoustics and vibration for aerospace applications. The Center was developed to support work being conducted at both NASA Langley Research Center and the commercial aviation sector. Programs within the Center will advance research in acoustic meta materials, wind turbine noise, and the medical application of acoustics. Current research thrusts are conducted in the areas of active noise control, advanced composite materials for noise reduction, and beam forming techniques.

Current Research Activities

Improved Acoustic Beam Forming Techniques for Wind Tunnel Applications:

Aircraft exterior noise is a critical impediment in the development of new aircraft systems, such as in supersonic commercial aircraft and in vehicles with a hybrid wing body. Beam forming has emerged as the measurement technique of choice when measuring aircraft noise using scaled models in wind tunnels, which is essential to validating and calibrating noise design software packages, such as ANOPP. The technique uses arrays of microphones, and has proven very successful, with much of the work being conducted by the AAB at NASA Langley Research Center. While the technique is effective, researchers in the Center for Aerospace Acoustics are working to improve its accuracy, resolution, and bandwith.

For this project, NIA students and researchers are working with Dr. Tom Brooks of NASA Langley, to test improved beam forming techniques. To improve the technique, work is being carried out to develop requisite theory and software to remove the effects of reflections from tunnel walls and background flow noise from signals on microphones. The removal of the aforementioned spurious signals will measurably improve results of beam form testing.

Future work will focus on validating these techniques by conducting planned tests in the Jet Noise Facility, as well as the 14 ft X 22 ft wind tunnel at NASA Langley. The anticipated major outcome of this project will be the ability to make beam forming techniques generally applicable to all wind tunnels, with the need for passive noise treatments such as lining the walls with acoustic tiles.

Related work is being conducted with Dr. Tom Brooks, developing new theory and approaches to reduce the influence of coherence on effects on accuracy. Forthcoming work will investigate and develop new approaches to take account of coherent sources; software will be developed and test in laboratory and wind tunnel environments.

Development of Acoustic Metamaterials:

The last 20 years has seen little-to-no substantial work in the development of innovative new acoustic materials, which would have increased sound absorption, be of lighter weight, and posses a thinner profile, than today’s standard. In order to effectively reduce aircraft frame noise, new materials will have to be developed.

The Center for Aerospace Acoustics at NIA is uniquely poised to lead investigations into the potential applications, and characteristics, of different acoustic metamaterials. These new materials will incorporate nano-embedded resonant elements to alter the wave propagation of the microwaves in order to increase absorption of diffract waves. Since microwaves and acoustic waves obey the same wave equation, there is potential to develop acoustic versions of metamaterials. Research thrusts into the application of nano materials are already underway in other research Centers at NIA, creating a collaborative environment, with a strong foundation in the development and application of nano materials.

Future work will investigate potential arangements of acoustic metamaterials using existing numerical models of poro-elastic materials with embedded masses, in addition to the dynamics of the MSD’s. Acoustic metamaterials will be constructed and tested in the reverberation chamber and Liner Technology Facility of the SAB at NASA Langley.

Energy Harvesting/Vibration Control Materials for Autonomous Space Explorers and Habitats:

Power consumption and weight of autonomous space explorers, such as rovers, are critical issues, which strongly influence the length of a mission, the robustness of the explorer, and the maneuverability of the system. In general, space systems carrying solar panels and other appendages, which tend to vibrate due to the motion of the vehicle. To control this vibration at acceptable levels so as not to break, and to perform at acceptable design levels, the supporting structure needs to be of added stiffness, thus adding weight to the vehicle design. Recent work at Virginia Tech has investigated the potential of a multi-functional material, which has the potential to damp out vibration by harvesting the vibrational energy into electrical power. This material is a development of the HG material, in which the static masses are replaced with small inertial linear electromagnetic generators of the same weight. Linear electromagnetic generators, which consist of a small, moveable, magnet enclosed in a small tube. The weight of this device is around 6 gm, and iti s about 2.5 cm in length. Preliminary testing at Virginia Tech indicates that the device, when excited by a vibration input of the order of 3g’s, can generate storable electrical energy that could be used to power a small sensor or electronic system.

Prediction and Control of Underwater Sound of Offshore Wind Turbine Farms:

Harnessing the power of the wind, in offshore environments, is a focus area for future growth in the Virginia State Government, and local industry, such as Northrop Grumman. A primary area of concern regarding the deployment of offshore wind turbines is the effect of wind turbine noise on marine life.

The Center for Aerospace Acoustics is equipped to spearhead investigations into the effects of underwater sound generated by offshore wind turbine farms on marine life. Funding is being sought from entities such as GE Wind Energy and the U.S. Department of Energy.

The proposed effort is a collaboration between Professor Fuller (NIA) and Professor Stewart Glegg (Florida Atlantic University), an international expert in wind turbine noise, and Dr. Kevin Shepherd (NASA LaRC). Dr. Shepherd is also an internationally recognized expert in wind turbine noise.

PVDF Wire Sensing on Intracranial Pressure:

PVDF wire is used to measure intracranial pressure in humans. The technology has potential to detect critical rises in ICP in astronauts in a non-invasive manner. Work is being conducted in collaboration with Eastern Virginia Medical School and represented a new thrust into medical applications of acoustics. A white paper has been submitted to NASA.

Active Control of Portable Generator Set Radiated Noise:

The aim of this project is to develop and apply an active noise control system for a U.S. Army portable generator set. It involves the measurement of the generator set noise, optimal design of the ANC system, construction of the ANC system, and the testing of the system’s performance. The system will provide around 5dBA in reduction of overall globally radiated sound.

PVDF Wire Sensor for External Measurement of Piping Interior Pressure:

Researchers in the Center for Aerospace Acoustics have adapted a PVDF wire sensor to externally measure the dynamic internal pressure of piping systems. This project involves analytical modeling and testing of the sensor on the actual piping system. The project was recently selected for a Phase II STTR program. It is supported by the ONR/NAVSEA.

Damping/Energy Harvesting of Vibrations Using a Distributed Vibration Absorber:

This project seeks to understand the dynamics of distributed vibration absorbers and how they simultaneously control vibration, harvest energy, and add electrical damping. The absorbers have been successfully modeled and tested on laboratory panel structures. This work is support by Newport News Shipbuilding.