• Dr. W. Nathan Alexander
  • Virginia Polytechnic Institute and State University
  • Holden Auditorium (Room 112)
  • 4:00 p.m.
  • Faculty Host: Dr. Michael Philen

The correlated response of rotor blades to ingested turbulence has been shown to generate broadband noise around the blade passage frequency and its harmonics. This noise is produced by the time-delay correlation of the unsteady lift response of each blade which in turn exerts an unsteady force on the surrounding acoustic medium. At zero-thrust conditions, convected turbulent structures pass through the disk plane with little distortion and noise can be predicted with reasonable accuracy knowing the inflow turbulence correlation function. When thrusting, the approach flow turbulence distorts as it is accelerated and, at high thrust, is stretched into long, thin filaments. In this case, the broadband response narrows and can even appear tonal. Accurate representation of the turbulence distortion is vital to predicting the broadband rotor noise, but this is not trivial, especially for complex flows which are inhomogeneous and anisotropic. This presentation details an experimental study in which a 457 mm diameter rotor was immersed in a thick turbulent boundary layer developed on the wall of the Virginia Tech Stability Wind Tunnel. Effects of turbulence distortion were observed through analysis of the noise and unsteady upwash. The influence of rotor yaw was also investigated.


Dr. W. Nathan Alexander received his PhD from Virginia Tech in 2011. He is currently a Research Assistant Professor at Virginia Tech studying aero/hydroacoustic noise sources and is a member of the Center for Renewable Energy and Aerodynamic Testing. His past research has focused on the noise produced by rotating machinery, airfoils, and rough surfaces as well as aeroacoustic measurement techniques.