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Experiments in Fluids

, Volume 25, Issue 5–6, pp 491–502 | Cite as

Laminarisation and re-transition of a turbulent boundary layer subjected to favourable pressure gradient

  • M. P. Escudier
  • A. Abdel-Hameed
  • M. W. Johnson
  • C. J. Sutcliffe

Abstract

 Experimental results are reported for the response of an initially turbulent boundary layer (Reθ≈1700) to a favourable pressure gradient with a peak value of K≡(−υ/ρU3 E ) dp/dx equal to 4.4×10-6. In the near-wall region of the boundary layer (y/δ<0.1) the turbulence intensity u′ scales roughly with the free-stream velocity U E until close to the location where K is a maximum whereas in the outer region u′ remains essentially frozen. Once the pressure gradient is relaxed, the turbulence level increases throughout the boundary layer until K falls to zero when the near wall u′ levels show a significant decrease. The intermittency γ is the clearest indicator of a fundamental change in the turbulence structure: once K exceeds 3×10-6, the value of γ in the immediate vicinity of the wall γ s falls rapidly from unity, reaches zero at the location where K again falls below 3×10-6 and then rises back to unity. Although γ is practically zero throughout the boundary layer in the vicinity of γ s =0, the turbulence level remains high. The explanation for what appears to be a contradiction is that the turbulent frequencies are too low to induce turbulent mixing. The mean velocity profile changes shape abruptly where K exceeds 3×10-6. Values for the skin friction coefficient, based upon hot-film measurements, peak at the same location as K and fall to a minimum close to the location where K drops back to zero.

Keywords

Boundary Layer Friction Coefficient Velocity Profile Skin Friction Turbulence Intensity 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 1998

Authors and Affiliations

  • M. P. Escudier
    • 1
  • A. Abdel-Hameed
    • 1
  • M. W. Johnson
    • 1
  • C. J. Sutcliffe
    • 1
  1. 1.Department of Engineering: Mechanical Engineering University of Liverpool Liverpool L69 3 BX, U.K.GB

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