PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows

Nezu, Iehisa; Sanjou, Michio

doi:10.1016/j.jher.2011.05.004

Cited by 62 publications

(26 citation statements)

References 30 publications

(56 reference statements)

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“…Since D x has the dimension [L 2 ⋅ T − 3 ], we can propose the relation

D_{x} \propto u_{*} g

. From the Reynolds stress intensity close to the wall boundary for turbulent open channel flows [ Nezu and Nakagawa , ; Nezu and Sanjou , ], u ∗ is derived and can be used as a scale for turbulence intensity near the bed [ Nezu and Rodi , ]. Following the above consideration and recalling the Townsend similarity on rough wall boundary layers [ Flack et al .…”

Section: Discussionmentioning

confidence: 99%

“…As a result of this, we have D x / u Ã . Since D x has the dimension [L 2 Á T À 3 ], we can propose the relation D x / u Ã g. From the Reynolds stress intensity close to the wall boundary for turbulent open channel flows [Nezu and Nakagawa, 1993;Nezu and Sanjou, 2011], u * is derived and can be used as a scale for turbulence intensity near the bed [Nezu and Rodi, 1986]. Following the above consideration and recalling the Townsend similarity on rough wall boundary layers [Flack et al 2005], the new parameter D x in our model can be interpreted as a measure of the turbulence intensity near the bed surface and may possibly be derived independently.…”

Section: Further Analysis Of the Parametersmentioning

confidence: 99%

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A mechanistic-stochastic formulation of bed load particle motions: From individual particle forces to the Fokker-Planck equation under low transport rates

Fan

Zhong

Wang

et al. 2014

J. Geophys. Res. Earth Surf.

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Bed load transport is a highly complex process. The probability density function (PDF) of particle velocities results from the local particle momentum variability in response to fluid drag and interactions with the bed. Starting from the forces exerted on a single particle under low transport rates (i.e., rolling and sliding regimes), we derive here the nonlinear stochastic Langevin equation (LE) to describe the dynamics of a single particle, accounting for both the deterministic and the stochastic components of such forces. Then, the Fokker-Planck equation (FPE), which describes the evolution of the PDF of the ensemble particle velocities, is derived from the LE. We show that the theoretical PDFs of both streamwise and cross-stream velocities obtained by solving the FPE under equilibrium conditions have exponential form (PDFs of both positive and negative velocities decay exponentially), consistent with the experimental data by Roseberry et al. (2012). Moreover, we theoretically show how the exponential-like PDF of an ensemble of particle velocities results from the forces exerted on a single particle. We also show that the simulated particle motions using the proposed Langevin model exhibit an emergent nonlinear relationship between hop distances and travel times (power law with exponent 5/3), in agreement with the experimental data, providing a statistical description of the particles' random motion in the context of a stochastic transport process. Finally, our study emphasizes that the motion of individual particles, described by the LE, and the behavior of the ensemble, described by the FPE, are connected within a statistical mechanics framework.

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“…Since D x has the dimension [L 2 ⋅ T − 3 ], we can propose the relation

D_{x} \propto u_{*} g

Section: Discussionmentioning

confidence: 99%

Section: Further Analysis Of the Parametersmentioning

confidence: 99%

A mechanistic-stochastic formulation of bed load particle motions: From individual particle forces to the Fokker-Planck equation under low transport rates

Fan

Zhong

Wang

et al. 2014

J. Geophys. Res. Earth Surf.

View full text Add to dashboard Cite

show abstract

“…The potential to characterize the turbulent structure of rivers at high spatial and temporal resolution, even if only at the surface, provides an opportunity to generate data that can be used to evaluate predictions of turbulent structure of river flow generated by numerical models. The advantage of LSPIV is that it can produce velocity information at a spatial resolution similar to that of numerical models, an endeavor that is difficult to accomplish using acoustic instruments [ Di Cicca et al ., ; Nezu and Sanjou , ]. LSPIV is especially well‐suited for turbulence analysis because of the near‐instantaneous nature of the collected data [ Hauet et al ., ; Nezu and Sanjou , ].…”

Section: Introductionmentioning

confidence: 99%

Resolving two‐dimensional flow structure in rivers using large‐scale particle image velocimetry: An example from a stream confluence

Lewis

Rhoads

2015

Water Resources Research

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Large-scale particle image velocimetry (LSPIV) has emerged as a valuable tool for measuring surface velocity in a variety of fluvial systems. LSPIV has typically been used in the field to obtain velocity or discharge measurements in relatively simple one-dimensional flow. Detailed two-dimensional or threedimensional characterization of flow structure has been relegated to laboratory settings because of the difficulty in controlling PIV limiting factors such as poor particle seeding, the need for camera rectification, and challenging field conditions. In this study we implement a low-cost LSPIV setup using a high-resolution action camera mounted above a stream confluence and water seeded with recycled landscape mulch. Time-averaged 2-D velocities derived from LSPIV are compared with those measured with an acoustic Doppler velocimeter (ADV) in the camera's field of view. We also assess the capabilities of this setup to resolve turbulent and time-averaged flow structures at a stream confluence. Our results reveal that even in challenging field conditions a basic LSPIV setup can yield accurate data on velocity and resolve in detail the temporal evolution of flow structures on the surface of rivers. The resulting dataset contains velocity information at high spatial and temporal resolution, a significant advance in understanding flow processes at stream confluences. Our LSPIV analysis provides support for previous numerical modeling studies that have distinguished between Kelvin-Helmholtz and wake modes of turbulent behavior within the mixing interface at confluences. This study shows that LSPIV can provide unprecedented levels of resolution of surface velocity patterns on rivers. Detailed velocity data derived from LSPIV can be used to evaluate numerical predictions of flow structure in complex fluvial environments.

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“…This system relies upon the measurement of the Doppler frequency shift of light scattered from an illuminating laser beam by particles entrained within the flow. It has also been widely used for open channel laboratory turbulence measurements (Ali et al 2013;Buchhave et al 1979;Nakagawa and Nezu 1987;Nezu and Rodi 1986;Nezu and Sanjou 2011;Tachie et al 2000;Tominaga and Nezu 1991), but it is infrequently used under field conditions because of its size. Deterioration of optical transmissions due to turbidity and higher cost also make its use lesser (Agrawal and Aubrey 1992;Agrawal and Belting 1988).…”

Section: Laser Doppler Velocimeter (Ldv)mentioning

confidence: 99%

Turbulence study in the vicinity of piano key weir: relevance, instrumentation, parameters and methods

Tiwari

Sharma

2015

Appl Water Sci

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This research paper focuses on the need of turbulence, instruments reliable to capture turbulence, different turbulence parameters and some advance methodology which can decompose various turbulence structures at different levels near hydraulic structures. Small-scale turbulence research has valid prospects in open channel flow. The relevance of the study is amplified as we introduce any hydraulic structure in the channel which disturbs the natural flow and creates discontinuity. To recover this discontinuity, the piano key weir (PKW) might be used with sloped keys. Constraints of empirical results in the vicinity of PKW necessitate extensive laboratory experiments with fair and reliable instrumentation techniques. Acoustic Doppler velocimeter was established to be best suited within range of some limitations using principal component analysis. Wavelet analysis is proposed to decompose the underlying turbulence structure in a better way.

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PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows

Cited by 62 publications

References 30 publications

A mechanistic-stochastic formulation of bed load particle motions: From individual particle forces to the Fokker-Planck equation under low transport rates

A mechanistic-stochastic formulation of bed load particle motions: From individual particle forces to the Fokker-Planck equation under low transport rates

Resolving two‐dimensional flow structure in rivers using large‐scale particle image velocimetry: An example from a stream confluence

Turbulence study in the vicinity of piano key weir: relevance, instrumentation, parameters and methods

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