On Tollmien-Schlichting-like waves in streaky boundary layers
2004 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 23, no 6, 815-833 p.Article in journal (Refereed) Published
The linear stability of the boundary layer developing on a flat plate in the presence of finite-amplitude, steady and spanwise periodic streamwise streaks is investigated. The streak amplitudes considered here are below the threshold for onset of the inviscid inflectional instability of sinuous perturbations. It is found that, as the amplitude of the streaks is increased, the most unstable viscous waves evolve from two-dimensional Tollmien-Schlichting waves into three-dimensional varicose fundamental modes which compare well with early experimental findings. The analysis of the growth rates of these modes confirms the stabilising effect of the streaks on the viscous instability and that this stabilising effect increases with the streak amplitude. Varicose subharmonic modes are also found to be unstable but they have growth rates which typically are an order of magnitude lower than those of fundamental modes. The perturbation kinetic energy production associated with the spanwise shear of the streaky flow is found to play an essential role in the observed stabilisation. The possible relevance of the streak stabilising role for applications in boundary layer transition delay is discussed.
Place, publisher, year, edition, pages
2004. Vol. 23, no 6, 815-833 p.
secondary instability, streamwise vortices, hydrodynamic stability, bypass transition, channel flows, energy growth, turbulence, disturbances, breakdown, plate
IdentifiersURN: urn:nbn:se:kth:diva-23876DOI: 10.1016/j.euromechflu.2004.05.001ISI: 000225066300002ScopusID: 2-s2.0-5144225991OAI: oai:DiVA.org:kth-23876DiVA: diva2:342575
QC 20100525 QC 201109152010-08-102010-08-102011-09-15Bibliographically approved