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http://hdl.handle.net/2289/5290
Title: | Mean-field dynamo action in renovating shearing flows |
Authors: | Kolekar, Sanved Subramanian, Kandaswamy Sridhar, S. |
Issue Date: | Aug-2012 |
Publisher: | American Physical Society |
Citation: | Physical Review E, 2012, Vol.86, 026303 |
Abstract: | We study mean-field dynamo action in renovating flows with finite and nonzero correlation time (τ) in the presence of shear. Previous results obtained when shear was absent are generalized to the case with shear. The question of whether the mean magnetic field can grow in the presence of shear and nonhelical turbulence, as seen in numerical simulations, is examined. We show in a general manner that, if the motions are strictly nonhelical, then such mean-field dynamo action is not possible. This result is not limited to low (fluid or magnetic) Reynolds numbers nor does it use any closure approximation; it only assumes that the flow renovates itself after each time interval τ. Specifying to a particular form of the renovating flow with helicity, we recover the standard dispersion relation of the α2Ω dynamo, in the small τ or large wavelength limit. Thus mean fields grow even in the presence of rapidly growing fluctuations, surprisingly, in a manner predicted by the standard quasilinear closure, even though such a closure is not strictly justified. Our work also suggests the possibility of obtaining mean-field dynamo growth in the presence of helicity fluctuations, although having a coherent helicity will be more efficient. |
Description: | Open Access |
URI: | http://hdl.handle.net/2289/5290 |
ISSN: | 1539-3755 1550-2376 (Online) |
Alternative Location: | http://adsabs.harvard.edu/abs/2012PhRvE..86b6303K http://arxiv.org/abs/1204.2714 http://dx.doi.org/10.1103/PhysRevE.86.026303 |
Copyright: | 2012 The American Physical Society |
Appears in Collections: | Research Papers (A&A) |
Files in This Item:
File | Description | Size | Format | |
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2012_PRE_86_026303.pdf | Open Access | 209.67 kB | Adobe PDF | View/Open |
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