The impact of intermittency on bed load sediment transport

Benavides, Santiago J.; Deal, Eric; Rushlow, Matthew; Venditti, Jeremy G.; Zhang, Qiong; Kamrin, Ken; Perron, J. Taylor

doi:10.31223/x5pw3q

Cited by 4 publications

(10 citation statements)

References 63 publications

(97 reference statements)

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“…The full description of the burst event offers us a better knowledge of turbulence intermittency, but how these indicators may be employed is still something that needs to be investigated further. For instance, Benavides et al (2021) defined waiting time in an indoor experiment study and used it to propose a new method for determining sediment initiation thresholds. The applicability of the indoor experimental results in nature environments remains to be verified in the future using more field data.…”

Section: Discussionmentioning

confidence: 99%

Turbulence Structure and Burst Events Observed in a Tidally Induced Bottom Boundary Layer

Voulgaris

Wang

2022

JGR Oceans

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As a three-dimensional vortex motion with high complexity, disorganization and randomness, turbulence is extremely unstable, unpredictable, and dissipative. With the development of fast responding observation techniques, researchers have carried out extensive research on various aspects of turbulence within the near-bottom boundary layer, including turbulent energy balance (Rippeth et al., 2001;Trowbridge et al., 1999) and intermittence characteristics (Wallace et al., 1972;Willmarth & Lu, 1972). The balance of turbulent kinetic energy (TKE) production and dissipation processes within the bottom boundary layer is controlled by horizontal TKE advection, buoyancy flux, vertical divergence, stratification, and other factors. Experimental verification of this balance has been the subject of numerous investigations (

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Section: Discussionmentioning

confidence: 99%

Turbulence Structure and Burst Events Observed in a Tidally Induced Bottom Boundary Layer

Voulgaris

Wang

2022

JGR Oceans

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“…Then it is quantified as a “rotation stress” whose profile is examined in different transport stages and further correlated to the transport relation. Our work here is benchmarked by flume experiments (Benavides et al., 2021; Deal et al., 2021) in which grain‐scale motions were tracked. (b) What is (not) responsible for the variability in the observed sediment transport relation?…”

Section: Bedload Transport Of Spherical Grainsmentioning

confidence: 99%

“…In the following discussion of the particle‐scale simulations, we first introduce the DEM‐LBM numerical method. Second, we present simulations matching the conditions of flume experiments (Benavides et al., 2021; Deal et al., 2021) to provide a relevant many‐particle test of the methodology. Third, we present wide wall‐free (WWF) simulations in order to study the factors that can potentially cause the variability seen in experimental transport data on gentle slopes.…”

Section: Discrete Simulationsmentioning

confidence: 99%

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Fluid‐Driven Transport of Round Sediment Particles: From Discrete Simulations to Continuum Modeling

et al. 2022

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Bedload sediment transport is ubiquitous in shaping natural and engineered landscapes, but the variability in the relation between sediment flux and driving factors is not well understood. At a given Shields number, the observed dimensionless transport rate can vary over a range in controlled systems and up to several orders of magnitude in natural streams. Here, we (a) experimentally validate a resolved fluid‐grain numerical scheme (Lattice Boltzmann Method‐Discrete Element Method or DEM‐LBM), and use it to (b) explore the parameter space controlling sediment transport in simple systems. Wide wall‐free simulations show the dimensionless transport rate is not influenced by the slope, fluid depth, mean particle size, particle surface friction, or grain‐grain damping for gentle slopes (0.01–0.03) at a medium to high fixed Shields number. (c) Examination of small‐scale fluid‐grain interactions shows fluid torque is non‐negligible for the entrainment and sediment transport near the threshold. And (d) the simulations guide the formulation of continuum models for the transport process. We present an upscaled two‐phase continuum model for grains in a turbulent fluid and validate it against bedload transport DEM‐LBM simulations. To model the creeping granular flow under the bed surface, we use an extension of the Nonlocal Granular Fluidity model, which was previously shown to account for flow cooperativity from grain‐size‐effects in dry media. The model accurately predicts the exponentially decaying velocity profile deeper into the bed.

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“…Although this is regarded as standard practice (e.g. Katul et al 1994;Chowdhuri et al 2020a;Benavides et al 2022), estimating the accuracy of the power-law exponent is not a trivial task and involves a lot of complicated steps (Clauset, Shalizi & Newman 2009). Nevertheless, to tackle this issue, we adopted a simple procedure.…”

Section: Persistence Pdfs Of Velocity Fluctuationsmentioning

confidence: 99%

A scale-wise analysis of intermittent momentum transport in dense canopy flows

2022

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We investigate the intermittent dynamics of momentum transport and its underlying time scales in the near-wall region of the neutrally stratified atmospheric boundary layer in the presence of a vegetation canopy. This is achieved through an empirical analysis of the persistence time scales (periods between successive zero-crossings) of momentum flux events, and their connection to the ejection–sweep cycle. Using high-frequency measurements from the GoAmazon campaign, spanning multiple heights within and above a dense canopy, the analysis suggests that, when the persistence time scales ( $t_p$ ) of momentum flux events from four different quadrants are separately normalized by $\varGamma _{w}$ (integral time scale of the vertical velocity), their distributions $P(t_p/\varGamma _{w})$ remain height-invariant. This result points to a persistent memory imposed by canopy-induced coherent structures, and to their role as an efficient momentum-transporting mechanism between the canopy airspace and the region immediately above. Moreover, $P(t_p/\varGamma _{w})$ exhibits a power-law scaling at times $t_{p}<\varGamma _{w}$ , with an exponential tail appearing for $t_{p} \geq \varGamma _{w}$ . By separating the flux events based on $t_p$ , we discover that around 80 % of the momentum is transported through the long-lived events ( $t_{p} \geq \varGamma _{w}$ ) at heights immediately above the canopy, while the short-lived ones ( $t_{p} < \varGamma _{w}$ ) only contribute marginally ( $\approx 20\,\%$ ). To explain the role of instantaneous flux amplitudes in momentum transport, we compare the measurements with newly developed surrogate data and establish that the range of time scales involved with amplitude variations in the fluxes tends to increase as one transitions from within to above the canopy.

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The impact of intermittency on bed load sediment transport

Cited by 4 publications

References 63 publications

Turbulence Structure and Burst Events Observed in a Tidally Induced Bottom Boundary Layer

Turbulence Structure and Burst Events Observed in a Tidally Induced Bottom Boundary Layer

Fluid‐Driven Transport of Round Sediment Particles: From Discrete Simulations to Continuum Modeling

A scale-wise analysis of intermittent momentum transport in dense canopy flows

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