Change search
ReferencesLink to record
Permanent link

Direct link
Surface tension induced global destabilization of plane jets and wakes
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The effect of surface tension on global stability of confined co-flow jets andwakes at a moderate Reynolds number is studied. The flow cases under studyare globally stable without surface tension. It is found that surface tensioncan cause the flow to be unstable if the inlet shear is strong enough. For evenstronger surface tension, the flow is re-stabilized. As long as there is no changeof the most unstable mode, increasing surface tension seems to decrease the oscillationfrequency and increase the wavelength of the mode. The critical shear(minimum shear at which an instability is found) is found to occur for antisymmetricdisturbances for the wakes and symmetric disturbances for the jets.However, at stronger shear, the opposite symmetry might be the most unstableone, in particular for wakes at high surface tension. The results show strongeffects of surface tension that should be possible to reproduce experimentallyas well as numerically.

URN: urn:nbn:se:kth:diva-34146OAI: diva2:419300
Available from: 2011-05-26 Created: 2011-05-26 Last updated: 2011-05-30Bibliographically approved
In thesis
1. Numerical stability studies of one-phase and immiscible two-phase jets and wakes
Open this publication in new window or tab >>Numerical stability studies of one-phase and immiscible two-phase jets and wakes
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The initial linear instability growth of two-dimensional plane wakes and jetsis investigated, by temporal two-dimensional global modes, and local spatialstability analysis. Comparisons are also made to experiments, direct numericalsimulations, and methods designed for weakly-non-parallel flows. The studiesproceed through three different flow setups with increasing complexity.The first flow analysed is a convectively unstable liquid sheet surroundedby a stagnant or co-flowing gas. The experimentally measured growth rates arefound to be in excellent agreement with spatial stability calculations, if the airboundary layer is taken into account, and not otherwise. The stabilizing effectof moderate air co-flow is quantified in the numerical study, and the governingparameters found to be the speed difference between water and air, and theshear from air at the water surface (inversely proportional to the air boundarylayer thickness).The second flow case is a one-phase confined wake, i.e. a wake in a channel.The effect of confinement (wall distance) on the global stability of wakes isanalysed by linear global modes, and compared to the results from DNS andweakly-non-parallel theory. At Re = 100, confinement is globally stabilizing,mostly due to a faster development towards a parabolic profile for confinedflows. The stabilizing effect of confinement almost disappears at Re ≈ 400.However, when the structural sensitivity of the wakes is analysed by an adjointbasedapproach, fundamental differences are seen in the global wavemakers ofconfined and unconfined wakes at Re ≈ 400.The third and most complex flow case is immiscible two-fluid wakes andjets. A parallel multi-domain spectral code is developed, where the kinematicand dynamic conditions on the interface are imposed as coupling conditions. Itis shown that intermediate values of surface tension can destabilize stable wakesand jets. In addition, surface tension has a considerable influence on the globaloscillation frequency and spatial shape of the global mode for unstable wakes.The character of the mode is gradually changed from a wake instability to aglobal shear layer instability. Both symmetric and antisymmetric modes areencountered for both wakes and jets, depending on the strength of the surfacetension (value of the Weber number) and the flow case.iii

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. ix, 93 p.
Trita-MEK, ISSN 0348-467X ; 11:07
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-34149 (URN)978-91-7501-051-9 (ISBN)
Public defence
2011-06-13, F3, Lindstedsvägen 206, KTH, Stockholm, 10:15 (English)
Swedish e‐Science Research Center
QC 20110530Available from: 2011-05-30 Created: 2011-05-26 Last updated: 2012-05-24Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Tammisola, OutiLundell, Fredrik
By organisation
MechanicsLinné Flow Center, FLOWWallenberg Wood Science Center

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 44 hits
ReferencesLink to record
Permanent link

Direct link