Scaling laws of passive tracer dispersion in the turbulent surface layer

Abstract

Experimental results for passive tracer dispersion in the turbulent surface layer under stable conditions are presented. In this case, the dispersion of tracer particles is determined by the interplay of three mechanisms: relative dispersion (celebrated Richardson's mechanism), shear dispersion (particle separation due to variation of the mean velocity field) and specific surface-layer dispersion (induced by the gradient of the energy dissipation rate in the turbulent surface layer). The latter mechanism results in the rather slow (ballistic) law for the mean squared particle separation. Based on a simplified Langevin equation for particle separation we found that the ballistic regime always dominates at large times. This conclusion is supported by our extensive atmospheric observations. Exit-time statistics are derived from the experimental data set and show a reasonable match with the simple dimensional asymptotes for different mechanisms of tracer dispersion, as well as predictions of the multifractal model and experimental data from other sources.

Evaluation and Tuning of Model Trajectories and Spreading Rates in the Baltic Sea Using Surface Drifter Observations

“…Therefore, the separation rate is governed by a ballistic law rather than Richardson's law in this situation. As none of these laws dominated, certain specific mechanisms, such as shear dispersion (particle separation due to spatial variations in the velocity field) or specific surface-layer dispersion (induced by the gradient of the energy dissipation rate in the turbulent surface layer, Skvortsov et al 2010) may govern the initial particle separation rate. Modelling of separations on small scales (Orre et al 2006) has revealed spreading rates slightly lower than expected, possibly due to the lateral boundaries affecting the drifters.…”

Tracer Dispersion in the Turbulent Convective Layer

“…The wall-bounded turbulent flow under the effect of changing stratification provides flexible settings to study the relative contribution of the buoyant and kinetic energy fluxes on scalar transport since this contribution can be easily controlled by varying the distance to the underlying surface (and passing the threshold of the Monin-Obukhov length) [2,7,9]. The results presented here are an extension of our previous study [11] conducted for the case of the neutrally stratified turbulent surface layer.…”

“…Due to the buoyancy effect and the associated anisotropy, convective turbulence produces much more complex phenomenology than the classical Kolmogorov model of isotropic turbulence and this imposes new challenges for its analytical treatment [1][2][3]. In spite of this complexity there has been remarkable progress in understanding this phenomena based on the application of modern methods of theoretical physics (see [4][5][6] for comprehensive reviews). Examples include the derivation of Kolmogorov and Bolgiano spectra in thermal convection, scaling of statistical moments of concentration, multi-fractal structure of tracer statistics and some others (see [2,[7][8][9][10] and references therein).…”

“…Various mechanisms of turbulent dispersion can be * alex.skvortsov@dsto.defence.gov.au characterized by the mean inter-particle distance [4][5][6]12]:…”

Scaling laws of peripheral mixing of passive scalar in a wall-shear layer

“…Starting with the seminal and pioneering work of Taylor [1], who calculated the diffusivity of a passive scalar in a turbulent flow, the subject of turbulent mixing has been always at the focus of research on turbulence and has undergone significant theoretical progress in recent years (see the comprehensive review by Falkovich et al [2] and references therein, as well as Refs. [3][4][5][6][7][8]). …”