Experiments in Fluids

, Volume 48, Issue 3, pp 431–440 | Cite as

Evolution of isolated streamwise vortices in the late stages of boundary layer transition

Research Article

Abstract

Experiments were conducted with two, smooth hills, lying well within the boundary layer over a flat plate mounted in a wind tunnel. One hill was shallow, with peak height 1.5 mm and width 50 mm; the other, steep, 3 mm high and 30 mm wide. Since the hills occupied one-half of the tunnel span, streamwise vorticity formed near the hills’ edge. At a freestream speed of 3.5 m/s, streaks formed with inflectional wall-normal and spanwise velocity profiles but without effecting transition. Transition, observed at 7.5 m/s, took different routes with the two hills. With the steep hill, streamwise velocity signals exhibited the passage of a wave packet which intensified before breakdown to turbulence. With the shallow hill there was a broad range of frequencies present immediately downstream of the hill. These fluctuations grew continuously and transition occurred within a shorter distance. Since the size of the streamwise vorticity generated at the hill edge is of the order of the hill height, the shallow hill generates vorticity closer to the wall and supports an earlier transition, whereas the steep hill creates a thicker vortex and associated streaks which exhibit oscillations due to their own instability as an additional precursor stage before transition.

References

  1. Acarlar MS, Smith CR (1987) A study of hairpin vortices in a laminar boundary layer. Part 1. Hairpin vortices generated by a hemisphere protuberance. J Fluid Mech 175:1–41CrossRefGoogle Scholar
  2. Asai M, Minagawa M, Nishioka M (2002) The instability and breakdown of a near-wall low-speed streak. J Fluid Mech 182:255–290Google Scholar
  3. Bakchinov AA, Grek GR, Klingmann BGB, Kozlov VV (1995) Transition experiments in a boundary layer with embedded streamwise vortices. Phys Fluids 7(820):820–832CrossRefGoogle Scholar
  4. Banerjee AS, Mandal AC, Dey J (2006) Particle image velocimetry studies of an incipient spot in the Blasius boundary layer. Exp Fluids 40(6):928–940CrossRefGoogle Scholar
  5. Boiko AV (2002) Receptivity of a flat plate boundary layer to a free stream axial vortex. Eur J Mech B/Fluids 21:325–340MATHCrossRefGoogle Scholar
  6. Durbin P, Wu XH (2007) Transition beneath vortical disturbances. Ann Rev Fluid Mech 39:107–128CrossRefMathSciNetGoogle Scholar
  7. Fransson JHM, Brandt L, Talamelli A, Cossu C (2004) Experimental and theoretical investigation of the nonmodal growth of steady streaks in a flat plate boundary layer. Phys Fluids 16(10):3627–3638CrossRefGoogle Scholar
  8. Hamilton JM, Abernathy FH (1994) Streamwise vortices and transition to turbulence. J Fluid Mech 264:185–212CrossRefGoogle Scholar
  9. Kachanov YS (1994) Physical mechanisms of laminar-boundary-layer transition. Ann Rev Fluid Mech 26:411–482MathSciNetGoogle Scholar
  10. Kendall JM (1985) Experimental study of disturbances produced in a pre-transitional laminar boundary layer by weak free-stream disurbances. AIAA Paper pp 85–1695Google Scholar
  11. Klebanoff PS, Tidstrom KD, Sargent LM (1962) The three dimensional nature of boundary-layer instability. J Fluid Mech 12(1):1–34MATHCrossRefGoogle Scholar
  12. Klebanoff PS, Cleveland WG, Tidstrom ISD (1992) On the evolution of a turbulent boundary layer induced by a three-dimensional roughness element. J Fluid Mech 237:101–187CrossRefGoogle Scholar
  13. Lourenco LM, Krothapalli A (2000) TRUE resolution PIV: a mesh-free second order accurate algorithm. In: Proceedings of the International Conference in applications of lasers to fluid mechanicsGoogle Scholar
  14. Luchini P (2000) Reynolds-number-independent instability of the boundary layer over a flat surface: optimal perturbations. J Fluid Mech 404:289–309MATHCrossRefMathSciNetGoogle Scholar
  15. Matsubara M, Alfredsson PH (2001) Disturbance growth in boundary layers subjected to free-stream turbulence. J Fluid Mech 430:149–168MATHCrossRefGoogle Scholar
  16. Narasimha R, Prasad SN (1994) Leading edge shape for flat plate boundary layer studies. Exp Fluids 17(5):358–360CrossRefGoogle Scholar
  17. Saric WS, Reed HL, Kerschen EJ (2002) Transition beneath vortical disturbances. Ann Rev Fluid Mech 34:291–319CrossRefMathSciNetGoogle Scholar
  18. Swearingen JD, Blackwelder RF (1987) The growth and breakdown of streamwise vortices in the presence of a wall. J Fluid Mech 182:255–290CrossRefGoogle Scholar
  19. Vasudevan KP, Dey J, Prabhu A (2001) Spot propagation characteristics in laterally strained boundary layers. Exp Fluids 30(5):488–491CrossRefGoogle Scholar
  20. Westin KJA, Boiko AV, Klingmann BGB, Kozlov VV, Alfredsson PH (1994) Experiments in a boundary layer subjected to free stream turbulence. Part 1. Boundary layer structure and receptivity. J Fluid Mech 281:193–218CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  1. 1.Department of Aerospace EngineeringIndian Institute of ScienceBangaloreIndia

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