Two-dimensional turbulence and dispersion in a freely decaying system
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Two-dimensional turbulence and dispersion in a freely decaying system. / Hansen, A. E.; Tabeling, P.
I: Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, Bind 58, Nr. 6, 1998, s. 7261-7271.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
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T1 - Two-dimensional turbulence and dispersion in a freely decaying system
AU - Hansen, A. E.
AU - Tabeling, P.
PY - 1998
Y1 - 1998
N2 - We report experimental results obtained on freely decaying two-dimensional turbulence. The flow is produced in a thin stratified layer of electrolyte, using an electromagnetic forcing. The velocity and vorticity fields are measured using a particle image velocimetry technique. The study of the temporal evolution of the system confirms in detail the scaling theory of Carnevale et al. [Phys. Rev. Lett. 66, 2735 (1991)]; the experimental value we find for the exponent characterizing the decay of the vortex density is [Formula Presented] We further measure the collision time [Formula Presented] the mean free path [Formula Presented] and the mean square displacement [Formula Presented] of the vortices. We find the following laws: [Formula Presented] and [Formula Presented] The statistics of passive particles (albeit virtual) in the system is also studied. They move hyperdiffusively, with an exponent similar to that obtained for the vortex motion. The dispersion of the particles is controlled by Lévy flights, produced by the jets formed by the dipoles. The distribution of flight times [Formula Presented] is [Formula Presented] Further analysis of the data indicates that the vortices undergo collisions whose geometrical aspects are analogous to those of an ordinary gas, and their motion is essentially Brownian diffusion in an expanding geometry. We finally underline the close relationship between the decay of turbulence and the dispersion phenomena.
AB - We report experimental results obtained on freely decaying two-dimensional turbulence. The flow is produced in a thin stratified layer of electrolyte, using an electromagnetic forcing. The velocity and vorticity fields are measured using a particle image velocimetry technique. The study of the temporal evolution of the system confirms in detail the scaling theory of Carnevale et al. [Phys. Rev. Lett. 66, 2735 (1991)]; the experimental value we find for the exponent characterizing the decay of the vortex density is [Formula Presented] We further measure the collision time [Formula Presented] the mean free path [Formula Presented] and the mean square displacement [Formula Presented] of the vortices. We find the following laws: [Formula Presented] and [Formula Presented] The statistics of passive particles (albeit virtual) in the system is also studied. They move hyperdiffusively, with an exponent similar to that obtained for the vortex motion. The dispersion of the particles is controlled by Lévy flights, produced by the jets formed by the dipoles. The distribution of flight times [Formula Presented] is [Formula Presented] Further analysis of the data indicates that the vortices undergo collisions whose geometrical aspects are analogous to those of an ordinary gas, and their motion is essentially Brownian diffusion in an expanding geometry. We finally underline the close relationship between the decay of turbulence and the dispersion phenomena.
UR - http://www.scopus.com/inward/record.url?scp=0001219484&partnerID=8YFLogxK
U2 - 10.1103/PhysRevE.58.7261
DO - 10.1103/PhysRevE.58.7261
M3 - Journal article
AN - SCOPUS:0001219484
VL - 58
SP - 7261
EP - 7271
JO - Physical Review E
JF - Physical Review E
SN - 2470-0045
IS - 6
ER -
ID: 332620745