Phased Array Processing for AAM Noise Flight Tests

In noise testing Advanced Aircraft Mobility vehicles, sound spheres represent directivity patterns. The current standard measurement approach is to fly or hover the vehicle over an array of microphones and project the microphone spectra onto the sphere. The quality of the results is limited by the finite number of microphones, uncontrolled acoustic propagation effects related to weather, and background noise.The proposed innovation models the complex acoustic source and radiation as a linear algebra problem and the latest techniques from signal processing are applied to produce much higher-quality results than the current state of the art. The results substantially improve the spatial fidelity of the radiation model. The influences of weather and aircraft source motion are tamed. A knob within the linear algebra offers the ability to neatly reject background noise, potentially permitting tests in suburban areas instead of remote desert locations.The work plan extends the software to get the most out of the method in simulations and plans a flight test for Phase II. The flight test will leverage a wireless microphone system developed by a subcontractor to this project under an earlier NASA SBIR.The subtopic for this proposed innovation is ldquo;A1.02: Quiet Performance - Airframe Noise (SBIR).rdquo; The specific bullet point is ldquo;Noise Analysis and Characterizationrdquo;:quot;Innovative source identification techniques for airframe (e.g., landing gear and high-lift systems) noise sources, including turbulence details related to flow-induced noise typical of separated flow regions, vortices, shear layers, etc. However, noise sources attributed solely to the engines are excluded from this call.quot;The term ldquo;airframe noiserdquo; does not exclude AAM noise work this year because the noise is not confined to engines and the NASA researchers who are working intensely with measurements of this type are mostly at LaRC, the lead Center for the call.