Title page for ETD etd-08102012-103032


Type of Document Master's Thesis
Author Morton, Michael Andrew
URN etd-08102012-103032
Title Rotor Inflow Noise Caused by a Boundary Layer: Inflow Measurements and Noise Predictions
Degree Master of Science
Department Aerospace and Ocean Engineering
Advisory Committee
Advisor Name Title
Devenport, William J. Committee Chair
Glegg, Stewart A. L. Committee Member
Lowe, Kevin Todd Committee Member
Keywords
  • turbulence ingestion
  • velocity correlation
  • haystacking
  • Turbulent boundary layer
  • rotor noise
Date of Defense 2012-08-02
Availability unrestricted
Abstract
A rotor immersed in a thick turbulent boundary layer produces unsteady loading on the blades which generates unwanted noise and vibration. Two point velocity fluctuations were measured in detail to determine the full four-dimensional correlation function of a boundary layer generated over a smooth wall in the Virginia Tech Stability Wind Tunnel. The correlation function reveals anisotropy in the flow dominated by a large scale correlation structure elongated in the streamwise direction and inclined relative to the wall. This correlation function was then evaluated in the blade frame of reference of an idealized 10 bladed rotor partially immersed in the flow. Blade to blade upwash coherence shows significant asymmetry which is a direct result of the anisotropy of the flow. Using a newly developed theory, the correlation function was used to predict the far-field radiated noise from the rotor at various operating and flow conditions. Predictions show the sound field is dominated by the effects of “haystacking” which is further increased with the inclusion of the presence of the wall. Directivity predictions suggest the far-field sound field acts like a monopole/dipole combination.
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