Impacts of macro-turbulent flow on sediment transport potential during ice-covered and open-channel conditions

2020 ◽  
Author(s):  
Eliisa Lotsari ◽  
Maria Kämäri ◽  
Petteri Alho ◽  
Elina Kasvi
Keyword(s):  
Sediment Transport ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Open Channel ◽  
Low Flow ◽  
The Arctic ◽  
Flow Structures ◽  
Channel Conditions ◽  
Total Sediment ◽  
Transport Potential

<p>Macro-turbulent flows during ice-covered and open-channel conditions, and their impacts on the total sediment transport, have not been studied widely in northern rivers. Previous studies have detected these processes, for example, only at the inlet area of one meander bend, or only during low discharge conditions. Thus, for understanding their impacts on the total sediment transport, it is needed to detect these macro-turbulent flow structures from a variety of cold region rivers, from multiple years, and also from a variety of different flow magnitude conditions. The pulses of high flow velocities related to these macro-turbulent structures may be important for determining the seasonal total sediment amount transported to the arctic ocean.</p><p> </p><p>The aim is 1) to detect the macro-turbulent flow in a meandering river at ice-covered low flow condition, and compare it to both high and low magnitude open-channel flow conditions. 2) Within a meander bend, the macro-turbulent flow will be compared between its inlet, apex and outlet sections. 3) The shear forces will be analyzed to detect the effects of macro-turbulent flow on potential sediment transport and channel development. The analyses are based on 5–10 minutes long moving boat Acoustic Doppler Current Profiler (ADCP) measurements from a meandering sub-arctic river. The measurements have been done in February and May during 2016–2019, and in September during 2016-2018. The preliminary results of this study are presented. The hypothesis is that the sediment transport potential of a sub-arctic river could be higher during all seasons than previously expected due to the pulses of high velocities related to macro-turbulent flow structures.</p>

scholarly journals Macro-Turbulent Flow and Its Impacts on Sediment Transport Potential of a Subarctic River during Ice-Covered and Open-Channel Conditions

Water ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1874
Author(s):  
Eliisa Lotsari ◽  
Michael Dietze ◽  
Maria Kämäri ◽  
Petteri Alho ◽  
Elina Kasvi
Keyword(s):  
Sediment Transport ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Velocity Fluctuation ◽  
Open Channel ◽  
Flow Characteristics ◽  
Bedload Transport ◽  
Low Flow ◽  
Critical Threshold ◽  
Flow Conditions

Macro-turbulent flows (i.e., coherent flow structures reaching through the whole water column), have not been studied widely in northern seasonally frozen rivers during both open-channel and ice-covered flow conditions. Thus, we aim: (1) to detect and compare the macro-turbulent flow, both at open-channel and ice-covered flow conditions; (2) to explore spatial variation of macro-turbulent flow characteristics within a meander bend; and (3) to detect the effects of near-bed layer velocity fluctuation on bedload transport during differing overall flow conditions. The analyses are based on 5–10 min-long acoustic Doppler current profiler (ADCP) measurements from a subarctic river. The ice-covered low flow, and open-channel higher and lower flow conditions were measured over the period of 2016 to 2020. This study found that macro-turbulent flow existed at all measurement locations under both open-channel and ice-covered flow conditions. Macro-turbulent flow was most consistent and obvious in the streamwise velocity component, and in particular at the inlet and outlet of the investigated meander bend. During all seasons, the near-bed velocities consistently exceeded the sufficient amount for sediment transport. At inlet and outlet areas, the greatest near-bed velocity fluctuation across the critical threshold for sediment transport coincided with the measurement times having frequent macro-turbulent flow.

Sediment transport to the Arctic Ocean and adjoining cold oceans*

2006 ◽  
Vol 37 (4-5) ◽  
pp. 413-432 ◽  
Author(s):  
Bent Hasholt ◽  
Nelly Bobrovitskaya ◽  
Jim Bogen ◽  
James McNamara ◽  
Sebastian H. Mernild ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Arctic Ocean ◽  
Monitoring Network ◽  
High Arctic ◽  
Sediment Flux ◽  
The Arctic ◽  
Sediment Loads ◽  
The Arctic Ocean ◽  
Available Information ◽  
Total Sediment

This paper reviews and synthesises available information on sediment transport to the Arctic Ocean and adjoining seas with open contact to the Atlantic and Pacific Oceans. Special emphasis is placed on calculation and estimation of the sediment flux from the mostly ungauged high Arctic areas on the American continent, in Greenland, and on islands in the Arctic Ocean, and from Russia. In the absence of reliable information on bedload fluxes for most rivers, attention is directed primarily to suspended sediment loads. By combining available monitoring data and estimates for ungauged areas, the total sediment transport to the Arctic Ocean is estimated to be 324–884 × 106 t yr−1. Of this total, a maximum of about 56% can be considered as monitored, while the rest is based on different types of estimate. It is clearly demonstrated that the monitoring network in the high Arctic is inadequate and that there is a lack of knowledge concerning the proportion of the load that actually reaches the sea, as well as bedload.

Analysis of turbulent flow structures in the straight rectangular open channel with floating vegetated islands

2020 ◽  
Vol 27 (21) ◽  
pp. 26856-26867
Author(s):  
Xuecheng Fu ◽  
Feifei Wang ◽  
Mengyang Liu ◽  
Wenxin Huai
Keyword(s):  
Turbulent Flow ◽  
Open Channel ◽  
Flow Structures

Particle motions near the bottom in turbulent flow in an open channel

1978 ◽  
Vol 86 (1) ◽  
pp. 109-127 ◽  
Author(s):  
B. Mutlu Sumer ◽  
Beyhan Oguz
Keyword(s):  
Turbulent Flow ◽  
Boundary Layers ◽  
Turbulent Flows ◽  
Particle Motion ◽  
Open Channel ◽  
Heavy Particle ◽  
Turbulent Boundary Layers ◽  
Particle Suspension ◽  
Photographic Technique ◽  
Bursting Process

A photographic technique has been used to make observations of the motion of heavy suspended particles in an open channel with a smooth bottom. The observations showed that the path of an individual heavy particle consists of an alternation between upward and downward paths traced by the particle as it travels close to the bottom. The path records appear to reveal most of the flow patterns near the wall shown up by earlier visualization observations; the measured kinematical quantities concerning the particle motion are in accord with those of earlier observations (e.g. Nychas, Hershey & Brodkey 1973). Making use of the present observations and following Offen & Kline's (1975) model of the bursting process in turbulent boundary layers, an attempt was made to explain the mechanism of particle suspension close to the wall in turbulent flows.

Impacts of frozen season and its possible future changes on the hydro- and morphodynamics of northern rivers

2020 ◽  
Author(s):  
Eliisa Lotsari
Keyword(s):  
Sediment Transport ◽  
Open Channel ◽  
Polar Region ◽  
Ice Cover ◽  
River Channel ◽  
The Arctic ◽  
River Ice ◽  
Freeze Thaw ◽  
The Future ◽  
Northern Rivers

<p>Global climate change is driving rapid changes in polar region, and significant attention has been given to predicting changes in precipitation and hydrology. However, warming will also alter sediment dynamics and drive morphological change as the melting of river and ground ice will mobilise floodplain and river channel sediments. The transport of this additional sediment can have a number of direct and indirect impacts on societies and ecosystems with yet unpredictable magnitude. There is a significant knowledge gap concerning how material is transported seasonally across such zones, and how the frozen season at present and its possible future changes affect the hydro- and morphodynamics of these northern rivers.</p><p>Therefore, it is needed <strong>1:</strong> To determine the impacts of varying river ice processes on seasonal hydrodynamics, sediment transport, and flood hazards in the high north;<strong> 2:</strong> To define the seasonal interlinkages and combined effects of sub-aerial (e.g., freeze-thaw, mass movements) and fluvial processes (e.g., ice-covered/open-channel flow) on morphodynamics, sediment transport and its origin in these seasonally ice-covered river systems.<strong> 3:</strong> To upscale reach scale seasonally-driven river morphodynamics to the watershed scale and simulate changes into the future, whilst defining the feedbacks between defrosting watersheds and total sediment load transported to the oceans.</p><p>This work is yet to be done, however, preliminary results are presented based on gathered pilot data and studies. Recent results have revealed that river ice can have the most significant role, greater than that of flowing water, in erosion and transport of coarse sediment from a sub-arctic river channel bed and its gently sloping banks. In addition, the findings from sandy meandering river suggest that certain ice cover conditions cause the vertical and lateral flow distribution to be opposite to the open channel situation. Thus, future changed river ice cover characteristics are expected to change these transport mechanisms and velocity distribution. This emphasizes that future predictions of river ice are needed, before predicting the changes in river morphology. However, it has been recently shown that thermal ice growth equation is not expected to work in the polar region in the future, as there is expected to be less snow and a higher number of freeze-thaw days in the future. In addition, adjustments to the ice decay equation and the applied parameter values would be needed for predicting ice decay processes in future. Under fast climatic warming of the arctic and subarctic, the shortening frozen period may also induce an earlier and prolonged season of bank erosion in meandering rivers, which further complicates the predictions of river morphodynamics. Thus, the use of improved hydro- and morphodynamic models and high-accuracy spatial and temporal data for better calibrating these models, are essential for detecting seasonally varying feedback effects of different interacting processes on river hydro-morphodynamics at present and in the future.</p>

Simulation and Modeling of Turbulent Flows

1996 ◽  
Keyword(s):  
Numerical Simulation ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Simulation And Modeling ◽  
Simulation Techniques ◽  
Rational Development ◽  
Group Methods ◽  
Turbulent Closure ◽  
The Subject ◽  
Renormalization Group Methods

This book provides students and researchers in fluid engineering with an up-to-date overview of turbulent flow research in the areas of simulation and modeling. A key element of the book is the systematic, rational development of turbulence closure models and related aspects of modern turbulent flow theory and prediction. Starting with a review of the spectral dynamics of homogenous and inhomogeneous turbulent flows, succeeding chapters deal with numerical simulation techniques, renormalization group methods and turbulent closure modeling. Each chapter is authored by recognized leaders in their respective fields, and each provides a thorough and cohesive treatment of the subject.

scholarly journals Large-eddy simulation of wall-bounded turbulent flow with high-order discrete unified gas-kinetic scheme

2020 ◽  
Vol 2 (1) ◽  
Author(s):  
Rui Zhang ◽  
Chengwen Zhong ◽  
Sha Liu ◽  
Congshan Zhuo
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Parallel Implementation ◽  
Kinetic Scheme ◽  
Cavity Flow ◽  
Equilibrium Distribution Function ◽  
Third Order ◽  
Two Stage ◽  
Large Eddy ◽  
Unified Gas Kinetic Scheme

AbstractIn this paper, we introduce the discrete Maxwellian equilibrium distribution function for incompressible flow and force term into the two-stage third-order Discrete Unified Gas-Kinetic Scheme (DUGKS) for simulating low-speed turbulent flows. The Wall-Adapting Local Eddy-viscosity (WALE) and Vreman sub-grid models for Large-Eddy Simulations (LES) of turbulent flows are coupled within the present framework. Meanwhile, the implicit LES are also presented to verify the effect of LES models. A parallel implementation strategy for the present framework is developed, and three canonical wall-bounded turbulent flow cases are investigated, including the fully developed turbulent channel flow at a friction Reynolds number (Re) about 180, the turbulent plane Couette flow at a friction Re number about 93 and lid-driven cubical cavity flow at a Re number of 12000. The turbulence statistics, including mean velocity, the r.m.s. fluctuations velocity, Reynolds stress, etc. are computed by the present approach. Their predictions match precisely with each other, and they are both in reasonable agreement with the benchmark data of DNS. Especially, the predicted flow physics of three-dimensional lid-driven cavity flow are consistent with the description from abundant literature. The present numerical results verify that the present two-stage third-order DUGKS-based LES method is capable for simulating inhomogeneous wall-bounded turbulent flows and getting reliable results with relatively coarse grids.

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