scholarly journals Towards a universal criteria for turbulence suppression in dilute turbidity currents with non-cohesive sediments

2012 ◽  
Vol 39 (14) ◽  
pp. n/a-n/a ◽  
Author(s):  
Mariano I. Cantero ◽  
Mrugesh Shringarpure ◽  
S. Balachandar
Keyword(s):  
Turbidity Currents ◽  
Cohesive Sediments ◽  
Turbulence Suppression

Dynamics of complete turbulence suppression in turbidity currents driven by monodisperse suspensions of sediment

2012 ◽  
Vol 712 ◽  
pp. 384-417 ◽  
Author(s):  
Mrugesh Shringarpure ◽  
Mariano I. Cantero ◽  
S. Balachandar
Keyword(s):  
Reynolds Stress ◽  
Suspended Sediments ◽  
Stable Stratification ◽  
Turbidity Currents ◽  
Vortical Structures ◽  
Threshold Size ◽  
Turbulence Suppression ◽  
Sediment Size ◽  
Ability To Regenerate ◽  
Monodisperse Suspensions

AbstractTurbidity currents derive their motion from the excess density imposed by suspended sediments. The settling tendency of sediments is countered by flow turbulence, which expends energy to keep them in suspension. This interaction leads to downward increasing concentration of suspended sediments (stable stratification) in the flow. Thus in a turbidity current sediments play the dual role of sustaining turbulence by driving the flow and damping turbulence due to stable stratification. By means of direct numerical simulations, it has been shown previously that stratification above a threshold can substantially reduce turbulence and possibly extinguish it. This study expands the simplified model by Cantero et al. (J. Geophys. Res., vol. 114, 2009a, C03008), and puts forth a proposition that explains the mechanism of complete turbulence suppression due to suspended sediments. In our simulations it is observed that suspensions of larger sediments lead to stronger stratification and, above a threshold size, induce an abrupt transition in the flow to complete turbulence suppression. It has been widely accepted that hairpin and quasi-streamwise vortices are key to sustaining turbulence in wall-bounded flows, and that only vortices of sufficiently strong intensity can spawn the next generation of vortices. This auto-generation mechanism keeps the flow populated with hairpin and quasi-streamwise vortical structures and thus sustains turbulence. From statistical analysis of Reynolds stress events and visualization of flow structures, it is observed that settling sediments damp the Reynolds stress events (Q2 events), which means a reduction in both the strength and spatial distribution of vortical structures. Beyond the threshold sediment size, the existing vortical structures in the flow are damped to an extent where they lose their ability to regenerate the subsequent generation of turbulent vortical structures, which ultimately leads to complete turbulence suppression.

Design options for self-cleansing storm sewers

1996 ◽  
Vol 33 (9) ◽  
pp. 215-220 ◽  
Author(s):  
Chandramouli Nalluri ◽  
Aminuddin Ab. Ghani
Keyword(s):  
Cohesive Sediments ◽  
Stress Criterion ◽  
Sediment Bed ◽  
Sediment Size ◽  
Codes Of Practice ◽  
Design Charts ◽  
Design Options ◽  
Minimum Velocity ◽  
Limited Depth ◽  
Storm Sewers

A list of available codes of practice for self-cleansing sewers is presented and a review of appraisals of minimum velocity criterion is summarised. Comparisons of newly developed “minimum velocity” criteria and “minimum shear stress” criterion are presented. Some design charts are also given. These charts are applicable to non-cohesive sediments (typically storm sewers). It appears that sediment size and concentration need to be taken into account, and that a limited depth of sediment bed is recommended for large pipes (diameters > 1000 mm) to maximise their transport capacity.

BED INSTABILITY GENERATED BY TURBIDITY CURRENTS

2018 ◽  
Vol 74 (4) ◽  
pp. I_1105-I_1110
Author(s):  
Sytharith PEN ◽  
Norihiro IZUMI ◽  
Sakura HAGISAWA
Keyword(s):  
Turbidity Currents

Pickup rate of non-cohesive sediments in low-velocity flows

2021 ◽  
pp. 1-11
Author(s):  
Dake Chen ◽  
Bruce Melville ◽  
Jinhai Zheng ◽  
Yigang Wang ◽  
Chi Zhang ◽  
...  
Keyword(s):  
Cohesive Sediments ◽  
Low Velocity

scholarly journals A Computationally Efficient Shallow Water Model for Mixed Cohesive and Non-Cohesive Sediment Transport in the Yangtze Estuary

Water ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1435
Author(s):  
Peng Hu ◽  
Junyu Tao ◽  
Aofei Ji ◽  
Wei Li ◽  
Zhiguo He
Keyword(s):  
Sediment Transport ◽  
Yangtze Estuary ◽  
Water Model ◽  
Cohesive Sediments ◽  
Shallow Water Model ◽  
Computationally Efficient ◽  
Time Step ◽  
The Yangtze Estuary ◽  
Erosion Coefficient ◽  
Cohesive Sediment Transport

In this paper, a computationally efficient shallow water model is developed for sediment transport in the Yangtze estuary by considering mixed cohesive and non-cohesive sediment transport. It is firstly shown that the model is capable of reproducing tidal-hydrodynamics in the estuarine region. Secondly, it is demonstrated that the observed temporal variation of suspended sediment concentration (SSC) for mixed cohesive and non-cohesive sediments can be well-captured by the model with calibrated parameters (i.e., critical shear stresses for erosion/deposition, erosion coefficient). Numerical comparative studies indicate that: (1) consideration of multiple sediment fraction (both cohesive and non-cohesive sediments) is important for accurate modeling of SSC in the Yangtze Estuary; (2) the critical shear stress and the erosion coefficient is shown to be site-dependent, for which intensive calibration may be required; and (3) the Deepwater Navigation Channel (DNC) project may lead to enhanced current velocity and thus reduced sediment deposition in the North Passage of the Yangtze Estuary. Finally, the implementation of the hybrid local time step/global maximum time step (LTS/GMaTS) (using LTS to update the hydro-sediment module but using GMaTS to update the morphodynamic module) can lead to a reduction of as high as 90% in the computational cost for the Yangtze Estuary. This advantage, along with its well-demonstrated quantitative accuracy, indicates that the present model should find wide applications in estuarine regions.

Deposition and erosion behaviour of cohesive sediments in the upper River Taw observatory, southwest UK: Implications for management and modelling

2021 ◽  
Vol 598 ◽  
pp. 126145
Author(s):  
M. Stone ◽  
B.G. Krishnappan ◽  
S. Granger ◽  
H.R. Upadhayay ◽  
Y. Zhang ◽  
...  
Keyword(s):  
Cohesive Sediments ◽  
Erosion Behaviour
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