Noise from a Rotor Ingesting a Planar Turbulent Boundary Layer

Abstract

This study concerns rotor noise generated by the ingestion of anisotropic, inhomogenous turbulence produced by a planar turbulent boundary layer. Far field noise was recorded at multiple receiving angles and blade wake profiles were measured for advance ratios ranging J=0.48 to 1.44. A novel method to infer the turbulence characteristics from the measured far field noise is presented. The time-frequency distribution of the recorded noise is used to estimate the streamwise scale of the turbulence while the time-averaged spectra are used to estimate the lateral scale. Results show that the estimated streamwise scale doubles over the measured range of advance ratios and the lateral scale remains approximately constant. This suggests a complex distortion of the turbulence due to the sheared flow and presence of the wall, a topic addressed in a companion paper (Glegg et al., 2013).