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Effects of Weak Free Stream Nonuniformity on Boundary Layer Transition (Keynote Paper)

[+] Author Affiliations
Jonathan H. Watmuff

Royal Melbourne Institute of Technology, Melbourne, VIC, Australia

Paper No. FEDSM2003-45685, pp. 1883-1892; 10 pages
  • ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference
  • Volume 1: Fora, Parts A, B, C, and D
  • Honolulu, Hawaii, USA, July 6–10, 2003
  • Conference Sponsors: Fluids Engineering Division
  • ISBN: 0-7918-3696-7 | eISBN: 0-7918-3673-8
  • Copyright © 2003 by ASME


Experiments are described in which well-defined FSN (Free Stream Nonuniformity) distributions are introduced by placing fine wires upstream of the leading edge of a flat plate. Large amplitude spanwise thickness variations are present in the downstream boundary layer resulting from the interaction of the laminar wakes with the leading edge. Regions of elevated background unsteadiness appear on either side of the peak layer thickness, which share many of the characteristics of Klebanoff modes, observed at elevated Free Stream Turbulence (FST) levels. However, for the low background disturbance level of the free stream, the layer remains laminar to the end of the test section (Rx ≈ l.4×106 ) and there is no evidence of bursting or other phenomena associated with breakdown to turbulence. A vibrating ribbon apparatus is used to demonstrate that the deformation of the mean flow is responsible for substantial phase and amplitude distortion of Tollmien-Schlichting (TS) waves. Pseudo-flow visualization of hot-wire data shows that the breakdown of the distorted waves is more complex and occurs at a lower Reynolds number than the breakdown of the K-type secondary instability observed when the FSN is not present.

Copyright © 2003 by ASME
Topics: Boundary layers



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