The Role of Impulse on the Initiation of Particle Movement Under Turbulent Flow Conditions

Diplas, Panayiotis; Dancey, Clinton L.; Çelik, Ahmet Ozan; Valyrakis, Manousos; Greer, Krista; Akar, Tanju

doi:10.1126/science.1158954

Cited by 296 publications

(291 citation statements)

References 20 publications

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“…This makes it of even greater utility and urgency to identify relevant criteria, which can be used and associated to riverbank stability. Further analysis using recently suggested event-based criteria for sediment transport, which appropriately accounts for the scales of coherent turbulent flow structures [53,54] and relevant modelling tools [24,25,55], would be also relevant to pursue in future studies. Such efforts should focus on investigating the potential of such criteria to better characterize the erosive capacity of flow turbulence on riverbanks, and find practical applications on vegetation flow hydrodynamics, engineering ecohydraulics and fluvial geomorphology.…”

Section: Implications For Riverbank Stabilitymentioning

confidence: 99%

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Valyrakis

Williams

2017

Water

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Riverbank vegetation is of high importance both for preserving the form (morphology) and function (ecology) of natural river systems. Revegetation of riverbanks is commonly used as a means of stream rehabilitation and management of bank instability and erosion. In this experimental study, the effect of different riverbank vegetation densities on flow hydrodynamics across the channel, including the riparian zone, are reported and discussed. The configuration of vegetation elements follows either linear or staggered arrangements as vegetation density is progressively increased, within a representative range of vegetation densities found in nature. Hydrodynamic measurements including mean streamwise velocity and turbulent intensity flow profiles are recorded via acoustic Doppler velocimetry (ADV)-both at the main channel and within the riverbank. These results show that for the main channel and the toe of riverbank, turbulence intensity for the low densities (λ ≈ 0 to 0.12 m −1 ) can increase up to 40% compared the case of high densities (λ = 0.94 to 1.9 m −1 ). Further analysis of these data allowed the estimation of bed-shear stresses, demonstrating 86% and 71% increase at the main channel and near the toe region, for increasing densities (λ = 0 to 1.9 m −1 ). Quantifying these hydrodynamic effects is important for assessing the contribution of physically representative ranges of riparian vegetation densities on hydrogeomorphologic feedback.

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Section: Implications For Riverbank Stabilitymentioning

confidence: 99%

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Valyrakis

Williams

2017

Water

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“…Note that some alternative studies have suggested that the governing variable to determine the critical condition for entrainment of a particle by a turbulent flow is an impulse rather than a force [20]. Here, where a laminar flow condition is present, the classical force approach can be reasonably kept nevertheless.…”

Section: Analysis a Onset Of Granular Erosionmentioning

confidence: 99%

Erosion onset of a cohesionless granular medium by an immersed impinging round jet

Brunier-Coulin¹,

Cuéllar²,

Philippe³

2017

Phys. Rev. Fluids

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To cite this version: AbstractAmong different devices developed quite recently to quantify the resistance to erosion of a natural soil within the broader context of dyke safety, the most commonly used is probably the Jet Erosion Test (JET) in which a scouring crater is induced by impingement of an immersed water jet. A comprehensive experimental investigation on the jet erosion in the specific situation of a cohesionless granular material is presented here. The tests were performed combining special optical techniques allowing for an accurate measurement of the scouring onset and evolution inside an artificially translucent granular sample. The impinging jet hydrodynamics are also analyzed empirically validating the use of a self-similar theoretical framework for the laminar round jet. The critical conditions at the onset of erosion appear to be best described by a dimensionless Shields number based on the inertial drag force created by the fluid flow on the eroded particles rather than on the pressure gradients around them. To conclude, a tentative empirical model for the maximal flow velocity initiating erosion at the bottom of the scoured crater is put forward and discussed in the light of some preliminary results.

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“…A recent study examined this phenomenon further under well controlled laboratory conditions and demonstrated that it is not the magnitude of the applied force alone that serves as the necessary and sufficient condition for particle entrainment but rather the combination of force and duration, or impulse. 25 The implication here is that the turbulence induced momentary peak forces acting on the bed material must last long enough to cause entrainment. Although results reported by Diplas et al 25 represent the behavior of a test particle in a well controlled environment, this conclusion implies that the impulse potential of a turbulent stream is relevant to the inception of bed material motion, rather than simply the magnitude of the instantaneous forces or timespace-averaged bed shear stress.…”

Section: Introductionmentioning

confidence: 99%

“…25 The implication here is that the turbulence induced momentary peak forces acting on the bed material must last long enough to cause entrainment. Although results reported by Diplas et al 25 represent the behavior of a test particle in a well controlled environment, this conclusion implies that the impulse potential of a turbulent stream is relevant to the inception of bed material motion, rather than simply the magnitude of the instantaneous forces or timespace-averaged bed shear stress.…”

Section: Introductionmentioning

confidence: 99%

Impulse and particle dislodgement under turbulent flow conditions

et al. 2010

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In this study, we investigated the role of turbulence fluctuations on the entrainment of a fully exposed grain near threshold flow conditions. Experiments were carried out to measure synchronously the near bed flow velocity and the particle movement for a range of flow conditions and resulting particle entrainment frequencies. We used a simplified bed geometry consisted of spherical particles to reduce the complexities associated with the variations in the bed and flow details in an effort to identify the underlying dominant physical mechanism. An analysis was performed based on common force approximations using near bed flow velocity. Turbulence fluctuations were treated as impulses, which are products of magnitude and duration of applied force. It is demonstrated that besides the magnitude of the instantaneous forces applied on a sediment grain, their duration is important as well in determining whether a particle will be entrained by a turbulent flow event. Frequency of particle entrainment varied remarkably with minute changes in gross flow parameters. Impulse imparted on the sediment grain by turbulent flow was found to be well represented by a log-normal distribution. We obtained a ͑log-normal͒ probability density function ͑pdf͒ dependent on only the coefficient of variation of the impulse ͑impulse intensity͒. Relation of the impulse intensity to the particle Reynolds number, Re ‫ء‬ , was established. The sensitivity of the computed impulse to the critical force level, as well as the influence of the critical impulse level on the dislodgement events, was explored. Particle entrainment probabilities were found using the derived pdf as well as experimental observations and a good agreement between the two is reported. Implications of the presented impulse concept and our experimental findings for sediment mobility at low bed shear stress conditions are also discussed.

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The Role of Impulse on the Initiation of Particle Movement Under Turbulent Flow Conditions

Cited by 296 publications

References 20 publications

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Erosion onset of a cohesionless granular medium by an immersed impinging round jet

Impulse and particle dislodgement under turbulent flow conditions

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