3D Lagrangian modelling of saltating particles diffusion in turbulent water flow

Bialik, Robert J.; Nikora, Vladimir; Rowiński, Paweł M.

doi:10.2478/s11600-012-0003-2

Cited by 53 publications

(70 citation statements)

References 33 publications

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“…Furthermore, recent studies highlighted that the scaling behavior within a particular scale range as well as the boundaries between the ranges may depend on specific transport conditions or motion modes [5,10,14,18,22]. For instance, the transition from the intermediate scale range to the global range, expressed in terms of tu Ã =d (t is time, u Ã is friction velocity, d is particle diameter) has been found to vary from tens [14,17] to hundreds [3,22]. This discrepancy is likely to be a result of using the same dimensionless argument tu Ã =d for all scale ranges while it may be applicable only at shorter times corresponding to the local and intermediate scale ranges where particle dynamics effects are dominant.…”

Section: Introductionmentioning

confidence: 99%

“…The available data advocate that this distribution is exponential [7,8,11] or follows the power law when the deposited particles are buried by other particles [14,15,20]. The information on the step length and resting time distributions can be incorporated in a deterministic Lagrangian model of saltating grains [3], which in turn can provide a basis for extensive numerical simulations for the identification of the diffusive behavior of particles at different time scales.…”

Section: Introductionmentioning

confidence: 99%

“…The objectives of this study therefore include: (1) identification of appropriate probability distributions for step lengths and resting times and expansion of a Lagrangian model of Bialik et al [3] by combining deterministic particle motion dynamics with these distributions; (2) identification of physically-relevant scaling for the time argument in the diffusion relationships suitable for particular ranges of scales; and (3) analysis of the statistical distributions and second-order statistics of particle trajectories, and quantification of diffusion regimes, extensions of the scaling ranges, and the boundaries between them.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper we analyze the diffusive properties of moving particles by superimposing particle trajectories considering instances of particle 'placement/release' on the bed as reference points (i.e., including some waiting time before first entrainment, Fig. 2a), rather than instances of direct entrainment (as in [3], Fig. 2b) or randomly selected points of particle-bed contact (as in [16,17], Fig.…”

Section: Introductionmentioning

confidence: 99%

“…This approach (i.e., Fig. 2a) permits identification of the 'near-field' diffusive behavior [1,3] instead of the pure ballistic diffusion of already saltating particles. In other words, at small diffusive times the 'near-field scale' associated with a particle trajectory just after its 'release' on the bed is explicitly resolved in our analysis.…”

Section: Introductionmentioning

confidence: 99%

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Diffusion of bedload particles in open-channel flows: distribution of travel times and second-order statistics of particle trajectories

et al. 2015

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The motion of bedload particles is diffusive and occurs within at least three scale ranges: local, intermediate and global, each of which with a distinctly different diffusion regime. However, these regimes, extensions of the scale ranges and boundaries between them remain to be better defined and quantified. These issues are explored using a Lagrangian model of saltating grains over the uniform fixed bed. The model combines deterministic particle motion dynamics with stochastic characteristics such as probability distributions of step lengths and resting times. Specifically, it is proposed that a memoryless exponential distribution is an appropriate model for the distribution of rest periods while the probability that a particle stops after a current jump follows a binomial distribution, which is a distribution with lack of memory as well. These distributions are incorporated in the deterministic Lagrangian model of saltating grains and extensive numerical simulations are conducted for the identification of the diffusive behavior of particles at different time scales. Based on the simulations and physical considerations, the local, intermediate, and global scale ranges are quantified and the transitions from one range to another are studied for a spectrum of motion parameters. The obtained results demonstrate that two different time scales should be considered for parameterization of diffusive behavior within intermediate and global scale ranges and for defining the localintermediate and intermediate-global boundaries. The simulations highlight the importance of the distributions of the step lengths and resting times for the identification of the boundaries (or transition intervals) between the scale ranges.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Diffusion of bedload particles in open-channel flows: distribution of travel times and second-order statistics of particle trajectories

et al. 2015

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Quantification of the bed load effects on turbulent open‐channel flows

Liu

et al. 2016

JGR Earth Surface

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With a computational model combining large eddy simulation and a discrete element model, detailed quantification of the bed load effects on turbulent open‐channel flows is presented. The objective is the revelation of bed load particle impact on the mean flow properties and coherent structures. Two comparative numerical experiments with mobile and immobile beds are conducted. Mean properties (e.g., velocity and Reynolds stress profiles) show good agreement with experimental data. Comparing the mobile and immobile cases, the effective bed position is nearly the same, whereas the equivalent sand roughness is changed. The flow experiences higher bottom shear stress over immobile bed. To quantify impact on turbulent structures, a revised quadrant analysis is performed to calculate four key parameters of ejection and sweep events (duration, maximum shear stress, transported momentum, and period). Results show that the ejection and sweep events have comparable importance in the outer region. However, sweep becomes dominant in the near‐wall region. The motion of particles enhances the sweep dominance by breaking up the ejection structures and decreasing their occurrence ratio. The results also suggest that the ejection events are easier to be influenced by the particle motions because they originate from the near‐wall region. The duration, maximum shear stress, and transported momentum decrease close to the bed. The period remains relatively constant in the outer region but decreases near the bed. Visualization of the coherent structure reveals that the instantaneous particle motion has strong correlation with the bursting cycle events.

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Exploring a semimechanistic episodic Langevin model for bed load transport: Emergence of normal and anomalous advection and diffusion regimes

Fan

Singh

Guala

et al. 2016

Water Resources Research

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Bed load transport is a highly stochastic, multiscale process, where particle advection and diffusion regimes are governed by the dynamics of each sediment grain during its motion and resting states. Having a quantitative understanding of the macroscale behavior emerging from the microscale interactions is important for proper model selection in the absence of individual grain-scale observations. Here we develop a semimechanistic sediment transport model based on individual particle dynamics, which incorporates the episodic movement (steps separated by rests) of sediment particles and study their macroscale behavior. By incorporating different types of probability distribution functions (PDFs) of particle resting times T r , under the assumption of thin-tailed PDF of particle velocities, we study the emergent behavior of particle advection and diffusion regimes across a wide range of spatial and temporal scales. For exponential PDFs of resting times T r , we observe normal advection and diffusion at long time scales. For a power-law PDF of resting times (i.e., f T r ð Þ$T 2m r ), the tail thickness parameter m is observed to affect the advection regimes (both sub and normal advective), and the diffusion regimes (both subdiffusive and superdiffusive). By comparing our semimechanistic model with two random walk models in the literature, we further suggest that in order to reproduce accurately the emerging diffusive regimes, the resting time model has to be coupled with a particle motion model able to produce finite particle velocities during steps, as the episodic model discussed here.

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3D Lagrangian modelling of saltating particles diffusion in turbulent water flow

Cited by 53 publications

References 33 publications

Diffusion of bedload particles in open-channel flows: distribution of travel times and second-order statistics of particle trajectories

Diffusion of bedload particles in open-channel flows: distribution of travel times and second-order statistics of particle trajectories

Quantification of the bed load effects on turbulent open‐channel flows

Exploring a semimechanistic episodic Langevin model for bed load transport: Emergence of normal and anomalous advection and diffusion regimes

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