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Surface tension-induced global instability of planar jets and wakes

Published online by Cambridge University Press:  31 October 2012

Outi Tammisola ,
Fredrik Lundell  and
L. Daniel Söderberg
Outi Tammisola
Affiliation:
Linné FLOW Center, KTH Mechanics, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
Fredrik Lundell
Affiliation:
Linné FLOW Center, KTH Mechanics, Royal Institute of Technology, SE-100 44 Stockholm, Sweden Wallenberg Wood Science Center, KTH Mechanics, SE-100 44 Stockholm, Sweden
L. Daniel Söderberg
Affiliation:
Wallenberg Wood Science Center, KTH Mechanics, SE-100 44 Stockholm, Sweden Innventia AB, Box 5604, SE-114 86, Stockholm, Sweden
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Abstract

The effect of surface tension on global stability of co-flow jets and wakes at a moderate Reynolds number is studied. The linear temporal two-dimensional global modes are computed without approximations. All but one of the flow cases under study are globally stable without surface tension. It is found that surface tension can cause the flow to be globally unstable if the inlet shear (or, equivalently, the inlet velocity ratio) is strong enough. For even stronger surface tension, the flow is restabilized. As long as there is no change of the most unstable mode, increasing surface tension decreases the oscillation frequency. Short waves appear in the high-shear region close to the nozzle, and their wavelength increases with increasing surface tension. The critical shear (the weakest inlet shear at which a global instability is found) gives rise to antisymmetric disturbances for the wakes and symmetric disturbances for the jets. However, at stronger shear, the opposite symmetry can be the most unstable one, in particular for wakes at high surface tension. The results show strong effects of surface tension that should be possible to reproduce experimentally as well as numerically.

JFM classification

Instability: Absolute/convective instability Interfacial Flows (free surface): Interfacial Flows (free surface) Wakes/Jets: Wakes/Jets
Type
Papers
Information
Journal of Fluid Mechanics , Volume 713 , 25 December 2012 , pp. 632 - 658
Copyright
©2012 Cambridge University Press

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