RESUMEN
As a turbulent flow advects a swarm of Lagrangian markers, the mutual separation between particles grows, and the shape of the swarm gets distorted. By following three points in an experimental turbulent two-dimensional flow with a k(-5/3) spectrum, we investigate the geometry of triangles, in a statistical sense. Two well-characterized shape distributions are identified. At long times when the average size of the triangles
RESUMEN
We report an experimental study of the dispersion of a passive tracer in the two-dimensional inverse energy cascade, which shows that a nonintermittent velocity field can sustain a strongly intermittent concentration field. The experiment suggests the exponents of the intermittent concentration field saturate at large orders towards xi(infinity) approximately 1.2. These observations are in excellent agreement with a recent numerical work [A. Celani, A. Lanotte, A. Mazzino, and M. Vergassola, Phys. Rev. Lett. 84, 2385 (2000)] and theoretical expectations [E. Balkovsky and V. Lebedev, Phys. Rev. E 58, 5776 (1998); V. Yakhot, ibid. 55, 329 (1997)].
RESUMEN
We report the first detailed experimental observation of the Batchelor regime [G. K. Batchelor, J. Fluid. Mech. 5, 113 (1959)], in which a passive scalar is dispersed by a large scale strain, at high Peclet numbers. The observation is performed in a controlled two-dimensional flow, forced at large scale, in conditions where a direct enstrophy cascade develops [J. Paret, M.-C. Jullien, and P. Tabeling, Phys. Rev. Lett. 83, 3418 (1999)]. The expected k(-1) spectrum is observed, along with exponential tails for the distributions of the concentration and concentration increments and logarithmlike behavior for the structure functions. These observations, confirmed by using simulated particles, provide a support to the theory.
RESUMEN
In the framework of chaotic scattering we analyze passive tracer transport in finite systems. In particular, we study models with open streamlines and a finite number of recirculation zones. In the nontrivial case with a small number of recirculation zones a description by means of asymptotic quantities (such as the eddy diffusivity) is not appropriate. The nonasymptotic properties of dispersion are characterized by means of the exit time statistics, which shows strong sensitivity on initial conditions. This yields a probability distribution function with long tails, making impossible a characterization in terms of a unique typical exit time. (c) 1999 American Institute of Physics.