On the mechanism of trailing vortex wandering

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Title: On the mechanism of trailing vortex wandering
Author(s): Edstrand, AM
Davis, TB
Schmid, PJ
Taira, K
Cattafesta, LN
Item Type: Journal Article
Abstract: The mechanism of trailing vortex wandering has long been debated and is often attributed to either wind-tunnel effects or an instability. Using particle image velocimetry data obtained in the wake of a NACA0012 airfoil, we remove the effect of wandering from the measured velocity field and, through a triple decomposition, recover the coherent wandering motion. Based on this wandering motion, the most energetic structures are computed using the proper orthogonal decomposition (POD) and exhibit a helical mode with an azimuthal wavenumber of |m|=1 whose kinetic energy grows monotonically in the downstream direction. To investigate the nature of the vortex wandering, we perform a spatial stability analysis of a matched Batchelor vortex. The primary stability mode is found to be marginally stable and nearly identical in both size and structure to the leading POD mode. The strikingly similar structure, coupled with the measured energy growth, supports the proposition that the vortex wandering is the result of an instability. We conclude that the cause of the wandering is the non-zero radial velocity of the |m|=1 mode on the vortex centreline, which acts to transversely displace the trailing vortex, as observed in experiments. However, the marginal nature of the stability mode prevents a definitive conclusion regarding the specific type of instability.
Publication Date: 19-Jul-2016
Date of Acceptance: 24-Jun-2016
URI: http://hdl.handle.net/10044/1/39077
DOI: http://dx.doi.org/10.1017/jfm.2016.440
ISSN: 0022-1120
Publisher: Cambridge University Press
Journal / Book Title: Journal of Fluid Mechanics
Volume: 801
Copyright Statement: © 2016 Cambridge University Press. This paper has been accepted for publication and will appear in a revised form, subsequent to peer-review and/or editorial input by Cambridge University Press.
Keywords: Fluids & Plasmas
01 Mathematical Sciences
09 Engineering
Publication Status: Published
Article Number: R1
Appears in Collections:Mathematics
Applied Mathematics and Mathematical Physics
Faculty of Natural Sciences



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