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The onset of instability in unsteady boundary-layer separation

Cassel, KW; Smith, FT; Walker, JDA; (1996) The onset of instability in unsteady boundary-layer separation. J FLUID MECH , 315 223 - 256. 10.1017/S0022112096002406. Green open access

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Abstract

The process of unsteady two-dimensional boundary-layer separation at high Reynolds number is considered. Solutions of the unsteady non-interactive boundary-layer equations are known to develop a generic separation singularity in regions where the pressure gradient is prescribed and adverse. As the boundary layer starts to separate from the surface, however, the external pressure distribution is altered through viscous-inviscid interaction just prior to the formation of the separation singularity; hitherto this has been referred to as the first interactive stage. A numerical solution of this stage is obtained here in Lagrangian coordinates. The solution is shown to exhibit a high-frequency inviscid instability resulting in an immediate finite-time breakdown of this stage. The presence of the instability is confirmed through a linear stability analysis. The implications for the theoretical description of unsteady boundary-layer separation are discussed, and it is suggested that the onset of interaction may occur much sooner than previously thought.

Type:Article
Title:The onset of instability in unsteady boundary-layer separation
Open access status:An open access version is available from UCL Discovery
DOI:10.1017/S0022112096002406
Publisher version:http://dx.doi.org/10.1017/S0022112096002406
Language:English
Additional information:© 1996 Cambridge University Press
Keywords:SINGULARITY FORMATION, RECTILINEAR VORTEX, HAIRPIN VORTICES, BREAK-UP, FLOW, CYLINDER, SHEET
UCL classification:UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Mathematics

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