Towards converged statistics in three-dimensional canopy-dominated flows

Chagot, Loïc; Moulin, F.; Eiff, Olivier

doi:10.1007/s00348-019-2857-4

Cited by 8 publications

(5 citation statements)

References 37 publications

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“…the region above the roughness crest where the dispersive shear stress still plays a role, is dependant on the geometry of the roughness. Very regular and dense canopies, for which the flow cannot reattach to the bottom between two successive roughness elements, induce a very weak dispersive shear stress outside the canopy (Chagot, Moulin & Eiff 2020). In the case of irregular canopies (Mignot, Hurther & Barthélemy 2009) or regular canopies for which the distance between the elements enables a reattachment of the flow to the bottom (Pokrajac et al 2007), the dispersive shear stress can be significant also outside the canopy.…”

Section: Double-averaged Flow Statisticsmentioning

confidence: 99%

Interaction between a rough bed and an adjacent smooth bed in open-channel flow

Dupuis,

Moulin,

Eiff

2023

J. Fluid Mech.

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Experiments are conducted in an open-channel flow where half of the section is smooth and the other half consists of an array of cubes, which are either submerged or emergent. A shear layer featuring large-scale Kelvin–Helmholtz structures develops between the two subsections. The flows are first analysed in the framework of the double-averaging method (averaging of the flow both in time and space). Double averaging could be performed thanks to an experimental set-up (three-dimensional, two-component telecentric scanning particle image velocimetry) that allows to measure the velocity field in a large volume, including the interstices between the cubes. A momentum balance performed on the smooth subsection indicates that the loss of momentum towards the rough subsection has the same order of magnitude than the momentum loss through bed friction. This lateral momentum flux occurs nearly exclusively through turbulent shear stress, whereas secondary currents plays a minor role and dispersive shear stress is negligible. A pattern recognition technique is then applied to investigate statistically the large-scale Kelvin–Helmholtz structures that develop in the shear layer. The structures appear to be coherent over the water depth and to be strongly inclined in the vertical, the top part being ahead. The educed coherent structure is responsible by itself for the shape of the velocity profile across the shear layer and for a large part of the turbulence (up to 60 % for the turbulent shear stress). Finally, a coupling is identified between the passage of the Kelvin–Helmholtz structures and the instantaneous wake flow around the cubes at the interface.

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Section: Double-averaged Flow Statisticsmentioning

confidence: 99%

Interaction between a rough bed and an adjacent smooth bed in open-channel flow

Dupuis,

Moulin,

Eiff

2023

J. Fluid Mech.

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“…This scenario is ubiquitous in nature (flows in rivers, over canopies or adjacent to biological surfaces such as feathers, for instance). Recent contributions demonstrated that all these flows exhibit a similar behaviour (Ghisalberti 2009;Keylock et al 2019;Bottaro 2019;Chagot et al 2020). However, there is no consensus for modelling such flows and this starts by notifying the existence of at least two school of thoughts for their theoretical examination: the homogenisation theory (Bottaro 2019) and the double averaging methodology (Nikora et al 2007).…”

Section: Introductionmentioning

confidence: 96%

Scanning PIV of turbulent flows over and through rough porous beds using refractive index matching

Rousseau

Ancey

2020

Exp Fluids

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This paper presents image velocimetry measurements on turbulent flows adjacent to a permeable bed made of randomly packed glass particles. For measuring flow velocities inside the bed, the refractive index of the glass particles was matched with that of the fluid. By continuously scanning in the transverse direction, we measured the streamwise and vertical velocity components within a three-dimensional domain (3D2C-PIV), including first-and second-order turbulent statistics. We established how the scanning travel speed is associated with the laser sheet thickness and the space-time velocity fluctuations for collecting reliable measurements. The methodology was applied to free-surface flows over a sloping bed under low relative submergence and supercritical conditions. Space-and time-averaged profiles were obtained in a representative elementary volume as defined by the double-averaging procedure (Nikora et al. in J Hydraulic Eng.127(2):123-133, 2001). A turbulent boundary layer over the rough bed was observed when experiments were run at intermediate Reynolds numbers Re = O(1000) . Apart from measuring subsurface velocities, this method shed light on the part played by the rough bed in the overall flow dynamics: the roughness layer was a buffer region within which porosity varied sharply and turbulent stress was rapidly dampened.

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“…To give just some examples, [1] proposes formula to determine the flow resistance, [2] used laboratory experiments to investigate the influence of composite roughness on flow resistance, [3] investigate the wide range of context made of the Bristh rivers. More recent works exist on such a topic with emergeant applications ranging from fish passes [4] to urban floods [5][6][7][8]. The present paper deals with this context.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, 1.4 million residents are exposed to the risk of marine submersion. Thus knowing how the flow behaves withing the housing settlement in relation to the submergence rate can be or practical consequence for safety services [8] have focused on high submergences, [9] on smaller ones. However experimental studies remain scarce.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the Hydraulics in Flooded Housing Estate

Doumic

Larrarte

Rtimi³

et al. 2022

Advances in Hydroinformatics

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Climate change is currently taking place at the scale of our planet, leading to aviolent response from the environment, particularly with regard to the water cycle. One of the risk is already floods. As an example, in France, the average annual costof damages caused by floods (and insured under the Natural Disaster plan) amountsto 520 million euros. In metropolitan France, nearly 17 million people, about aquarter of the national population, are exposed to the risk of flooding by overflowaccording to the preliminary flood risk assessment carried out by the State in 2011.And with climate evolution, floods will become more frequent and more intense. Onechallenge during floods is to be able to access to people refugee over buildings.In order to investigate the hydraulic context generated by the grouped obstaclesrepresentative of a submerged housing estate, both an experimental and numericalstudy is being conducted.We experimentally study the flow in the presence of rows of macro-roughnessesrepresentative of a slightly emerged and of a submerged housing estate, and this forsituations representing both current and more intense floods. Measurements of the velocity field will provide information on currents distribution that might affect an evacuation process. In parallel a numerical study is also conducted with the opensource code Saturne. The nuemerical results are compared to experimental results and this preliminary stupy opens the way to a systematic investigation.

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Towards converged statistics in three-dimensional canopy-dominated flows

Cited by 8 publications

References 37 publications

Interaction between a rough bed and an adjacent smooth bed in open-channel flow

Interaction between a rough bed and an adjacent smooth bed in open-channel flow

Scanning PIV of turbulent flows over and through rough porous beds using refractive index matching

Investigation of the Hydraulics in Flooded Housing Estate

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