Phased Array Measurements of Scaled Propellers through a Wind Tunnel Shear Layer

As part of the second phase of the Vertical Lift Propeller Noise Test (VLPNT), several propeller/proprotor geometries were measured in the NASA Langley 14- by 22-Foot Subsonic Tunnel (14x22) in its semi-open jet, acoustically treated configuration. Blade geometries were chosen to be representative of those used in the emerging Future Vertical Lift (FVL) and Urban Air Mobility (UAM) industries. Performance and acoustic measurements were taken of the propellers at high incidence angles, simulated descent conditions, and for dynamic pitching maneuvers intended to emulate portions of a tilting rotor’s transition envelope. A 54-microphone phased array was deployed to isolate targeted acoustic sources while rejecting background noise. A time-domain beamforming algorithm, the ROtating Source Identifier (ROSI), was used to track and acoustically image the rotating blades. Advantages and limitations of the ROSI method are discussed. shear layer correction methods are applied to the data. Additionally, advanced beamforming algorithms are explored to improve resolution and enhance source localization.