Eur. Phys. J. B 20, 427-440 (2001)
https://doi.org/10.1007/s100510170261

Passive tracer dynamics in 4 point-vortex flow

¹ Dipartimento di Energetica "S. Stecco", Università degli Studi di Firenze, INFN and INFM, Via di Santa Marta 3, 50139 Firenze, Italy
² Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, NY 10012, USA
³ Lefschetz Center for Dynamical Systems, Division of Applied Mathematics, Brown University, Providence, RI 02912, USA
⁴ Department of Physics, New York University, 2-4 Washington Place, New York, NY 10003, USA

Corresponding author: ^a leoncini@cims.nyu.edu

Received: 28 September 2000
Revised: 9 February 2001
Published online: 15 April 2001

Abstract

The advection of passive tracers in a system of 4 identical point vortices is studied when the motion of the vortices is chaotic. The phenomenon of vortex-pairing has been observed and statistics of the pairing time is computed. The distribution exhibits a power-law tail with exponent implying finite average pairing time. This exponents is in agreement with its computed analytical estimate of . Tracer motion is studied for a chosen initial condition of the vortex system. Accessible phase space is investigated. The size of the cores around the vortices is well approximated by the minimum inter-vortex distance and stickiness to these cores is observed. We investigate the origin of stickiness which we link to the phenomenon of vortex pairing and jumps of tracers between cores. Motion within the core is considered and fluctuations are shown to scale with tracer-vortex distance as . No outward or inward diffusion of tracers are observed. This investigation allows the separation of the accessible phase space in four distinct regions, each with its own specific properties: the region within the cores, the reunion of the periphery of all cores, the region where vortex motion is restricted and finally the far-field region. We speculate that the stickiness to the cores induced by vortex-pairings influences the long-time behavior of tracers and their anomalous diffusion.