Journal ArticleDOI
Criteria for the selection of stochastic models of particle trajectories in turbulent flows
TLDR
In this paper, the relationships between the various criteria are examined for a very general class of models and it is shown that most of the criteria are equivalent and also how a model can be designed to satisfy these criteria exactly and to be consistent with inertial-subrange theory.Abstract:
Many different random-walk models of dispersion in inhomogeneous or unsteady turbulence have been proposed and several criteria have emerged to distinguish good models from bad. In this paper the relationships between the various criteria are examined for a very general class of models and it is shown that most of the criteria are equivalent. It is also shown how a model can be designed to satisfy these criteria exactly and to be consistent with inertial-subrange theory. Some examples of models that obey the criteria are described. As an illustration some calculations of dispersion in free-convective conditions are presented.read more
Citations
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Book ChapterDOI
Numerical modelling of the turbulent dispersion of heavy particles: inertia and gravity effects on turbulent diffusivity
Journal ArticleDOI
Footprint characteristics of scalar concentration in the convective boundary layer
Guo Xiaofeng,Cai Xuhui +1 more
TL;DR: In this article, a backward Lagrangian stochastic (LS) dispersion model and a large eddy simulation (LES) model are used in the investigation of footprint characteristics for passive scalar concentration in the convective boundary layer (CBL).
Numerical Modeling Of Collision And Agglomeration Of Adhesive Particles In Turbulent Flows
Abstract: Particle motion, clustering and agglomeration play an important role in natural phenomena and industrial processes. In classical computational fluid dynamics (CFD), there are three major methods which can be used to predict the flow field and consequently the behavior of particles in flow-fields: 1) direct numerical simulation (DNS) which is very expensive and time consuming, 2) large eddy simulation (LES) which resolves the large scale but not the small scale fluctuations, and 3) ReynoldsAveraged Navier-Stokes (RANS) which can only predict the mean flow. In order to make LES and RANS usable for studying the behavior of small suspended particles, we need to introduce small scale fluctuations to these models, since these small scales have a huge impact on the particle behavior. The first part of this dissertation both extends and critically examines a new method for the generation of small scale fluctuations for use with RANS simulations. This method, called the stochastic vortex structure (SVS) method, uses a series of randomly positioned and oriented vortex tubes to induce the small-scale fluctuating flow. We first use SVS in isotropic homogenous turbulence and validate the predicted flow characteristics and collision and agglomeration of particles from the SVS model with full DNS computations. The calculation speed for the induced velocity from the vortex structures is improved by about two orders of magnitude using a combination of the fast multiple method and a local Taylor series expansion. Next we turn to the problem of extension of the SVS method to more general turbulent flows. We propose an inverse method by which the initial vortex orientation can be specified to generate a specific anisotropic Reynolds stress field. The proposed method is validated for turbulence measures and colliding particle transport in comparison to DNS for turbulent jet flow. The second part of the dissertation uses DNS to examine in more detail two issues raised during developing the SVS model. The first issue concerns the effect of two-way coupling on the agglomeration of adhesive particles. The SVS model as developed to date does not account for the effect of particles on the flow-field (one-way coupling). We focused on examination of the local flow around agglomerates and the effect of agglomeration on modulation of the turbulence. The second issue examines the microphysics of turbulent agglomeration by examining breakup and collision of agglomerates in a shear flow. DNS results are reported both for one agglomerate in shear and for collision of two agglomerates, with a focus on the physics and role of the particleinduced flow field on the particle dynamics.
Computational tools for the simulation of atmospheric pollution events
TL;DR: Aguirre et al. as discussed by the authors presented the Centro de Investigaciones Cientificas y Transferencia de Tecnologia a la Produccion.
Journal ArticleDOI
On the upward flux of sea‐spray spume droplets in high‐wind conditions
TL;DR: In this article, the vertical transport of spume droplets in the high-wind atmospheric boundary layer (ABL) is studied and simulated based on observational data and the characteristics of high wind ABL above the ocean.
References
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Journal ArticleDOI
An Introduction to Probability Theory and Its Applications.
Journal ArticleDOI
Turbulence Structure in the Convective Boundary Layer
TL;DR: In this paper, a boundary layer experiment conducted over a flat site in northwestern Minnesota is discussed, where wind and temperature fluctuations near the ground were measured with AFCRL's fast-response instrumentation on a 32 m tower with MRU probes attached at five different heights to the tethering cable of a 1300 m2 kite balloon.
Book
Theory and Applications of Stochastic Differential Equations
Zeev Schuss,Robert O'Malley +1 more
TL;DR: Presents theory, sources, and applications of stochastic differential equations of Ito's type; those containing white noise; and the role of partial differential equations in this context.