Experiments in Fluids

, Volume 25, Issue 5, pp 491–502

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

DOI: 10.1007/s003480050255

Cite this article as:
Escudier, M., Abdel-Hameed, A., Johnson, M. et al. Experiments in Fluids (1998) 25: 491. doi:10.1007/s003480050255

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/ρU3E) 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 UE 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 γs 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 γs=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.

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