Non-local dispersion and the reassessment of Richardson's t3-scaling law
arXiv:2307.01746 · doi:10.1017/jfm.2021.989
Abstract
The Richardson scaling law states that the mean square separation of a fluid particle pair grows according to t3 within the inertial range and at intermediate times. The theories predicting this scaling regime assume that the pair separation is within the inertial range and that the dispersion is local, meaning that only eddies at the scale of the separation contribute. These assumptions ignore the structural organization of the turbulent flow into large-scale shear layers, where the intense small-scale motions are bounded by the large-scale energetic motions. Therefore, the large scales contribute to the velocity difference across the small-scale structures. It is shown that, indeed, the pair dispersion inside these layers is highly non-local and approaches Taylor dispersion in a way that is fundamentally different from the Richardson scaling law. Also, the layer's contribution to the overall mean square separation remains significant as the Reynolds number increases. This calls into question the validity of the theoretical assumptions. Moreover, a literature survey reveals that, so far, t3 scaling is not observed for initial separations within the inertial range. We propose that the intermediate pair dispersion regime is a transition region that connects the initial Batchelor- with the final Taylor-dispersion regime. Such a simple interpretation is shown to be consistent with observations, and is able to explain why t3 scaling is found only for one specific initial separation outside the inertial range. Moreover, the model incorporates the observed non-local contribution to the dispersion, because it requires only small-time-scale properties and large-scale properties.
References in corpus (13)
- Particles and fields in fluid turbulence
- Fluid Particle Accelerations in Fully Developed Turbulence
- Experimental study of inertial particles clustering and settling in homogeneous turbulence
- Timescales of Turbulent Relative Dispersion
- Extreme events in the dispersions of two neighboring particles under the influence of fluid turbulence
- Geometry and violent events in turbulent pair dispersion
- Effects of Reynolds Number and Stokes Number on Particle-pair Relative Velocity in Isotropic Turbulence: A Systematic Experimental Study
- Turbulent pair dispersion as a continuous-time random walk
- Experimental Study of the Bottleneck in Fully Developed Turbulence
- Relative dispersion of particle pairs in turbulent channel flow
- Generalization of Turbulent Pair Dispersion to Large Initial Separations
- Dust Coagulation Regulated by Turbulent Clustering in Protoplanetary Disks
- How tracer particles sample the complexity of turbulence