Title page for ETD etd-02022012-152048


Type of Document Master's Thesis
Author Forest, Jonathan Bradley
Author's Email Address jforest@vt.edu
URN etd-02022012-152048
Title The Wall Pressure Spectrum of High Reynolds Number Rough-Wall Turbulent Boundary Layers
Degree Master of Science
Department Aerospace and Ocean Engineering
Advisory Committee
Advisor Name Title
Devenport, William J. Committee Chair
Anderson, Jason Committee Member
Lowe, Kevin Todd Committee Member
Schetz, Joseph A. Committee Member
Keywords
  • high Reynolds number
  • rough wall
  • turbulent boundary layer
  • surface pressure
Date of Defense 2012-01-19
Availability unrestricted
Abstract
The presence of roughness on a surface subject to high Reynolds number flows promotes the formation of a turbulent boundary layer and the generation of a fluctuating pressure field imposed on the surface. While numerous studies have investigated the wall pressure fluctuations over zero-pressure gradient smooth walls, few studies have examined the effects of surface roughness on the wall pressure field. Additionally, due to the difficulties in obtaining high Reynolds number flows over fully rough surfaces in laboratory settings, an even fewer number of studies have investigated this phenomenon under flow conditions predicted to be fully free of transitional effects that would ensure similarity laws could be observed. This study presents the efforts to scale and describe the wall pressure spectrum of a rough wall, high Reynolds number turbulent boundary layer free of transitional effects. Measurements were taken in the Virginia Tech Stability Wind Tunnel for both smooth and rough walls. A deterministic roughness fetch composed of 3-mm hemispheres arranged in a 16.5-mm square array was used for the rough surface. Smooth and rough wall flows were examined achieving Reynolds numbers up to Reθ = 68700 and Reθ = 80200 respectively, with the rough wall flows reaching roughness based Reynolds numbers up to kg+ = 507 with a simultaneous blockage ratio of δ/kg = 76. A new roughness based inner variable scaling is proposed that provides a much more complete collapse of the rough wall pressure spectra than previous scales had provided over a large range of Reynolds numbers and roughness configurations. This scaling implies the presence of two separate time scales associated with the near wall turbulence structure generation. A clearly defined overlap region was observed for the rough wall surface pressure spectra displaying a frequency dependence of ω-1.33, believed to be a function of the surface roughness configuration and its associated transport of turbulent energy. The rough wall pressure spectra were shown to decay more rapidly, but based on the same function as what defined the smooth wall decay.
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