Continuous-Scan Phased Array Measurement Methods for Turbofan Engine Acoustic Testing

To allow aviation growth to continue in the face of increasingly stringent noise pollution standards, new aircraft engines must be designed with noise performance as a principal constraint. Technologies to realize future propulsion noise reduction will require detailed experimental characterization and diagnosis of the acoustic mechanisms and sources within an engine system or component. ATA Engineering, Inc. (ATA) proposes an SBIR project to further develop and validate methods for obtaining phased array acoustic data from complex distributed noise sources using continuously moving, or continuous-scan (CS) microphones in conjunction with state-of-the-art phase-referencing techniques. The benefits of the CS method include (1) effectively infinite spatial resolution, as the sound field cross-spectrum may be described between any two locations along the scan trajectory, (2) preservation of phase data for improved source and propagation modeling, including beamforming (BF) and acoustical holography (AH), (3) significant reduction of test data acquisition time (potentially two to ten times faster) per operational point, and consequently either (4) reduced test operational cost, or (5) the opportunity to screen more design concepts within a given budget. The Phase II effort will use subscale aeroacoustic testing to validate the novel continuous-scan beamforming (CSBF) measurement techniques with the aim of eventual implementation in NASA acoustic wind tunnel and free-jet testing facilities. ATA will also formalize a CS software toolkit for data processing and visualization and design a full-scale array concept for a candidate NASA wind tunnel facility.