A hybrid wing body transport aircraft model was tested in NASA Langley's 14 by 22Foot Subsonic Tunnel to evaluate proposed "low noise" technology. The experiment was set up to evaluate the community noise impact of the hybrid wing body design, as well as study the noise components of propulsion-airframe noise and shielding. A high fidelity 5.8-percent scale model, including landing gear, cruise and drooped wing leading edges, trailing edge elevons, vertical tail options, and engine noise simulators, was built to test both aerodynamic and acoustic configurations. The aerodynamic test data were used to establish appropriate flight conditions for the acoustic test.To accomplish the acoustic portion of this test, two major upgrades were required of NASA Langley's 14 by 22 Foot Subsonic Tunnel; first, a fuel delivery system to provide realistic gas temperatures to the jet engine simulators; and second, a traversing microphone array and side towers to measure full spectral and directivity noise characteristics.The results of this test provide benchmark hybrid wing body aircraft and noise shielding data to assist in achieving NASA's 2020 noise emission goals. I.
NASA's current predictive capabilities using the ray tracing program (RTP) are validated using helicopter noise data taken at Eglin Air Force Base in 2007. By including refractive propagation effects due to wind and temperature, the ray tracing code is able to explain large variations in the data observed during the flight test.
NASA is investigating acoustic propagation capabilities to accommodate a point to point propagation prediction scheme defining a ray between a specific source–observer pair in an inhomogeneous stratified atmosphere with wind. A 4D space-time ray method based on the null geodesic equations yields two main benefits over classical 3D Euclidian reduced ray equations: (1) it poses a valid two point boundary value problem for the rays connecting two locations; and (2) the solution method is valid throughout the whole domain including at ray turning points without the need for piecewise definitions. The resulting two point boundary value problem and the constant horizontal slowness vectors, which are a result of the stratified medium assumption, allow the desired (t, x, y, z) ray trace. The presentation highlights the equations and inputs required to solve the 4D ray trace. The solution to this two point boundary value problem will create the groundwork for efficient future NASA propagation codes.
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