Title: Short-wave instability growth in closely spaced vortex pairs

Authors: Nicholas Boustead, Kris Ryan, Gregory J. Sheard

Addresses: Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, VIC 3800, Australia. ' Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, VIC 3800, Australia. ' Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, VIC 3800, Australia

Abstract: The growth of short-wave elliptical instabilities in a Lamb-Oseen vortex pair subject to non-uniform strain fields at close vortex spacing is considered using direct numerical simulation at a Reynolds number Re = 20000. A linear stability analysis demonstrates that with reduced vortex spacing the growth rate of all axial wave-numbers is enhanced relative to that of the fastest-growing mode. A coupling of vortices is observed at close vortex spacing, which may lead to improved non-linear instability growth, and the development of fluid cross-over regions. These fluid cross-over regions are shown to be products of a linear growth regime.

Keywords: elliptic instability; growth rate; Lamb-Oseen vortex pair; linear stability analysis; fluid cross-over; aircraft wakes; short-wave instability; strain; numerical simulation; vortex spacing.

DOI: 10.1504/PCFD.2010.035360

Progress in Computational Fluid Dynamics, An International Journal, 2010 Vol.10 No.5/6, pp.276 - 283

Published online: 26 Sep 2010 *

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