University of Surrey

Test tubes in the lab Research in the ATI Dance Research

Discrete linear local eigenmodes in a separating laminar boundary layer

Marxen, O, Lang, M and Rist, U (2012) Discrete linear local eigenmodes in a separating laminar boundary layer Journal of Fluid Mechanics, 711. pp. 1-26.

Full text not available from this repository.

Abstract

The evolution of two- and three-dimensional small-amplitude disturbances in the laminar part of a laminar separation bubble is investigated in detail. We apply a combination of local linear stability theory, results from different experimental measurement campaigns and direct numerical simulations to identify two different discrete eigenmodes in the laminar part of the bubble. A stable eigenmode, the outer mode, governs unsteady oscillations in the upstream part of the bubble. However, this perturbation is quickly overtaken by an unstable eigenmode, the inner mode, which eventually leads to transition of the detached shear layer. Such a behaviour is observed due to an acceleration region with a favourable pressure gradient preceding the adverse-pressure-gradient region. The flow is stable in the acceleration region, in which the outer mode is only moderately damped, while the inner mode is strongly damped. At the onset of instability for the unstable eigenmode upstream of separation, both viscous Tollmien-Schlichting and inviscid Kelvin-Helmholtz instability mechanisms contribute to amplification, while deeper inside the bubble only the inviscid mechanism is active. If the explicit forcing is moved to a region downstream of the favourable pressure gradient, only the unstable eigenmode appears. The same behaviour is found for two-dimensional and weakly oblique waves. © 2012 Cambridge University Press.

Item Type: Article
Authors :
NameEmailORCID
Marxen, Oo.marxen@surrey.ac.ukUNSPECIFIED
Lang, MUNSPECIFIEDUNSPECIFIED
Rist, UUNSPECIFIEDUNSPECIFIED
Date : 1 November 2012
Identification Number : 10.1017/jfm.2012.263
Depositing User : Symplectic Elements
Date Deposited : 17 May 2017 13:28
Last Modified : 17 May 2017 15:11
URI: http://epubs.surrey.ac.uk/id/eprint/839324

Actions (login required)

View Item View Item

Downloads

Downloads per month over past year


Information about this web site

© The University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom.
+44 (0)1483 300800