Passive boundary layer control of oblique distrubances by finite-amplitude streaks
2014 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 749, 1-36 p.Article in journal (Refereed) Published
Recent experimental results on the attenuation of two-dimensional Tollmien-Schlichting wave (TSW) disturbances by means of passive miniature vortex generators (MVGs) have shed new light on the possibility of delaying transition to turbulence and hence accomplishing skin-friction drag reduction. A recurrent concern has been whether this passive flow control strategy would work for other types of disturbances than plane TSWs in an experimental configuration where the incoming disturbance is allowed to fully interact with the MVG array. In the present experimental investigation we show that not only TSW disturbances are attenuated, but also three-dimensional single oblique wave (SOW) and pair of oblique waves (POW) disturbances are quenched in the presence of MVGs, and that transition delay can be obtained successfully. For the SOW disturbance an unusual interaction between the wave and the MVGs occurs, leading to a split of the wave with one part travelling with a 'mirrored' phase angle with respect to the spanwise direction on one side of the MVG centreline. This gives rise to 3-vortices on the centreline, which force a low-speed streak on the centreline, strong enough to overcome the high-speed streak generated by the MVGs themselves. Both these streaky boundary layers seem to act stabilizing on unsteady perturbations. The challenge in a passive control method making use of a non-modal type of disturbances to attenuate modal disturbances lies in generating stable streamwise streaks which do not themselves break down to turbulence.
Place, publisher, year, edition, pages
2014. Vol. 749, 1-36 p.
boundary layer control, boundary layer stability, transition to turbulence
Fluid Mechanics and Acoustics
IdentifiersURN: urn:nbn:se:kth:diva-121270DOI: 10.1017/jfm.2014.211ISI: 000337922700001ScopusID: 2-s2.0-84901017405OAI: oai:DiVA.org:kth-121270DiVA: diva2:617622
FunderEU, European Research Council
QC 20140806. Updated from manuscript to article in journal.2013-04-242013-04-242016-02-08Bibliographically approved