Micro scale exchange processes between surface and subsurface water

Vollmer, Stefan; Ramos, Francisco de los Santos; Daebel, Helge; Kühn, Gregor

doi:10.1016/s0022-1694(02)00190-7

Cited by 64 publications

(68 citation statements)

References 7 publications

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“…[4][5][6][7][8][9][10][11][12] In contrast, due to technical difficulties and heavy computational costs, the number of experiments and numerical simulations explicitly designed for investigating the transition layer between a turbulent boundary layer and a porous medium region is much more limited. [13][14][15]3 Ruff and Gelhar 13 performed velocity measurements in pipe flows where the porous medium was composed of foam. Velocities were measured by means of hot-wire anemometry.…”

Section: B Turbulence Properties Of the Transition Layermentioning

confidence: 99%

“…Another experimental attempt to gain insight into the turbulence characteristics of the subsurface flow was presented by Vollmer et al, 15 where pressure fluctuations were measured at different levels within a gravel bed of an open channel flow, in order to investigate the effects of coherent structures on the exchange of solutes between the surface and subsurface flows. The rms of pressure fluctuations were found to decrease exponentially inside the bed where the high frequency components of the pressure signal vanished more rapidly than low frequency components.…”

Section: B Turbulence Properties Of the Transition Layermentioning

confidence: 99%

“…It is clear that the properties of turbulence within the transition layer have been poorly investigated. In particular, experimental studies on this topic are scarce ͑only the studies from Ruff and Gelhar 13 and Vollmer et al 15 provided some insight͒. More needs to be done to provide data for future model validations and also to gain more insight into the transport mechanisms responsible for the coupling between the surface and the subsurface flow.…”

Section: B Turbulence Properties Of the Transition Layermentioning

confidence: 99%

“…Such concept was first introduced in Ref. 15 where pressure fluctuations were measured within a gravel bed underneath an open channel flow. The rms of the pressure fluctuations were observed to quickly decrease within the bed and it was found that the bed dissipated high frequency fluctuations faster than the low frequency components; the signal of which was instead persistent even at the lowest bed levels.…”

Section: -9mentioning

confidence: 99%

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Turbulence structure of open channel flows over permeable and impermeable beds: A comparative study

Manes

Pokrajac²,

McEwan³

et al. 2009

Physics of Fluids

126

146

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The behavior of turbulent open channel flows over permeable surfaces is not well understood. In particular, it is not clear how the surface and the subsurface flow within the permeable bed interact and influence each other. In order to clarify this issue we carried out two sets of experiments, one involving velocity measurements in open channel flows over an impermeable bed composed of a single layer of spheres, and another one where velocities were measured over and within a permeable bed made of five such layers. Comparison of surface flow velocity statistics between the two sets of experiments confirmed that bed permeability can significantly affect flow resistance. It was also confirmed that even in the hydraulically rough regime, the friction factors for the permeable bed increase with increasing Reynolds number. Such an increase in flow resistance implies a different distribution of normal form-induced stress between the permeable and impermeable bed cases. Subsurface flow measurements performed within the permeable bed revealed that there is an intense transport of turbulent kinetic energy ͑TKE͒ occurring from the surface to the subsurface flow. We provide evidence that the transport of TKE toward the lower bed levels is driven mainly by pressure fluctuations, whereas TKE transport due to turbulent velocity fluctuations is limited to a thinner layer placed in the upper part of the bed. It was also confirmed that the turbulence imposed by the surface flow gradually dissipates while penetrating within the porous medium. Dissipation occurs faster for the small scales than for the large ones, which instead are persistent, although weak, even at the lowest bed levels.

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Section: B Turbulence Properties Of the Transition Layermentioning

confidence: 99%

Section: B Turbulence Properties Of the Transition Layermentioning

confidence: 99%

Section: B Turbulence Properties Of the Transition Layermentioning

confidence: 99%

Section: -9mentioning

confidence: 99%

See 2 more Smart Citations

Turbulence structure of open channel flows over permeable and impermeable beds: A comparative study

Manes

Pokrajac²,

McEwan³

et al. 2009

Physics of Fluids

126

146

View full text Add to dashboard Cite

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“…[1][2][3][4][5][6][7][8][9] In contrast, due to experimental difficulties and highly demanding computational costs, laboratory investigations and numerical simulations of the turbulent flow inside permeable beds are very limited. [10][11][12][13] This stimulated the authors to carry out a series of experiments designed to investigate turbulence properties at the interface between turbulent open channel flows and a porous bed. The internal geometry of the porous bed was chosen to allow velocity measurements within its voids and to maintain acceptable similarity with gravel beds of natural streams.…”

mentioning

confidence: 99%

Peculiar mean velocity profiles within a porous bed of an open channel

2007

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We present the velocity profile measured within a porous bed below rough turbulent open channel flow. Mean streamwise velocity has a minimum in the top pore, just below the bed surface, and then increases towards a constant value in the deeper pores. We argue that the velocity minimum in the top pore is due to enhanced turbulence generated within the external flow. This produces a flow regime similar to rough turbulent pipe flow, with very efficient momentum extraction. In the deeper pores turbulence intensities are damped so that momentum extraction is less efficient, allowing higher mean velocities to develop. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2780193͔For fluid flowing over and inside a rough permeable bed, the flow domain can be divided into a "free-stream" region above the bed and a subsurface region within it. Many studies have been carried out for the case of laminar subsurface flows. [1][2][3][4][5][6][7][8][9] In contrast, due to experimental difficulties and highly demanding computational costs, laboratory investigations and numerical simulations of the turbulent flow inside permeable beds are very limited. [10][11][12][13] This stimulated the authors to carry out a series of experiments designed to investigate turbulence properties at the interface between turbulent open channel flows and a porous bed. The internal geometry of the porous bed was chosen to allow velocity measurements within its voids and to maintain acceptable similarity with gravel beds of natural streams. For these purposes, the porous bed comprised uniform size spheres packed in cubic arrangement with each successive layer of spheres placed directly on top of the preceding one.This Brief Communication focuses on mean streamwise velocity profiles measured within the bed. The profiles show a peculiar velocity minimum just one bead diameter below the bed surface. This was consistently found in all the experiments by two independent measurement techniques. This result is counterintuitive since one would expect mean velocities to decrease uniformly within the bed due to the weakening of the shearing effect induced by the free-stream flow. In the following text we provide an explanation for this unexpected result.Experiments were conducted using an 11-m-long and 0.4-m-wide tilting hydraulic flume with a rectangular cross section. The permeable bed used in this study consisted of five layers of 12-mm-diam glass spheres packed in a cubic pattern. All experiments were carried out under uniform turbulent flow conditions. The main hydraulic parameters for the experiments are shown in Table I. Velocities were measured using an ultrasonic velocity profiler ͑UVP͒ and particle image velocimetry ͑PIV͒.Subsurface velocities were measured by means of a 4-MHz Met-Flow UVP probe ͑Met-Flow SA 2000͒, which was inserted in a hole drilled in the bed and oriented along the flow, as shown in Fig. 1. In these experiments, the probe measured instantaneous velocities at 128 points within a length of about 95 mm. Each measurement point corresp...

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A Model for Mass Transport Across the Sediment‐Water Interface

Voermans

Ghisalberti

Ivey

2018

Water Resources Research

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Molecular diffusion, dispersion, and turbulent diffusion can all contribute to the transport of mass across the sediment‐water interface (SWI). Flow observations across the SWI are critical in the description of these transport processes but are currently very limited as the sediment bed is inaccessible in most experimental approaches. We overcome this constraint by combining refractive‐index matching (RIM) with particle‐tracking velocimetry (PTV). Using measurements of the flow dynamics across the SWI, we propose a mechanistic model that describes the interfacial mass transport over a wide and relevant parameter space. We show there are three transport regimes where molecular, dispersive, or turbulent transport dominates the mass flux of a passive tracer across the SWI. Transitions between these regimes are defined by the permeability Reynolds number ReK=Ku∗/ν, where K is the sediment permeability, u∗ is the shear velocity, and ν is the fluid viscosity. In the molecular regime ( ReK≤O(0.01)), mass transport is described by the molecular diffusion coefficient (D). In both the dispersive ( O(0.01)

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Micro scale exchange processes between surface and subsurface water

Cited by 64 publications

References 7 publications

Turbulence structure of open channel flows over permeable and impermeable beds: A comparative study

Turbulence structure of open channel flows over permeable and impermeable beds: A comparative study

Peculiar mean velocity profiles within a porous bed of an open channel

A Model for Mass Transport Across the Sediment‐Water Interface

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