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Experimental investigation of streaky structures in a relaminarizing boundary layer
KTH, Superseded Departments, Mechanics.ORCID iD: 0000-0002-1146-3241
2002 (English)In: Journal of turbulence, ISSN 1468-5248, Vol. 3Article in journal (Refereed) Published
Abstract [en]

An experimental investigation of a boundary layer subjected to a relaminarization process is performed. The initially turbulent boundary layer develops on a plate mounted inside a two-dimensional convergent channel, and the results show that the mean velocity profiles of the boundary layer develop towards the self-similar laminar solution. Two-point correlation measurements, performed by means of two miniaturized single-wire hot-wire probes with variable relative spanwise separation, show the presence of elongated longitudinal structures. The absolute spanwise separation of these streaks decreases in the downstream direction. However, if the size is normalized with the displacement thickness of the boundary layer, the relative streak spacing shows a significant increase. Also, when scaled with the viscous length scale l* the streak spacing (defined as average distance between low- and high-speed streaks) increases from about 60l* in the turbulent boundary layer to 150-180l* in the relaminarizing region. To process only the laminar part of the velocity signals a filtering procedure based on a threshold value of the second derivative of the time signals has been applied showing a slight increase in the detected spanwise scales. Finally, measurements were carried out at an enhanced level of free stream turbulence. Although small differences can be observed, the results are qualitatively similar to the ones obtained at a low level of free stream turbulence.

Place, publisher, year, edition, pages
2002. Vol. 3
Keyword [en]
favorable pressure-gradient, reynolds-number
URN: urn:nbn:se:kth:diva-21417ISI: 000174623800001OAI: diva2:340115
QC 20100525Available from: 2010-08-10 Created: 2010-08-10Bibliographically approved

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