scholarly journals Visualization of Large-scale Coherent Structure in an Turbulent Open Channel Flow

1991 ◽  
Vol 11 (Supplement2) ◽  
pp. 209-212
Author(s):  
Takanori SAGA ◽  
Hirofumi OHNARI ◽  
Katsutoshi WATANABE ◽  
Takashi SAITOU
Keyword(s):  
Channel Flow ◽  
Coherent Structure ◽  
Large Scale ◽  
Open Channel ◽  
Open Channel Flow

scholarly journals Drag forces on a bed particle in open-channel flow: effects of pressure spatial fluctuations and very-large-scale motions

2019 ◽  
Vol 863 ◽  
pp. 494-512 ◽  
Author(s):  
S. M. Cameron ◽  
V. I. Nikora ◽  
I. Marusic
Keyword(s):  
Channel Flow ◽  
Drag Force ◽  
High Frequency ◽  
Large Scale ◽  
Open Channel ◽  
Low Frequency ◽  
Open Channel Flow ◽  
Stereoscopic Particle Image Velocimetry ◽  
Force Fluctuations ◽  
Drag Forces

The fluctuating drag forces acting on spherical roughness elements comprising the bed of an open-channel flow have been recorded along with synchronous measurements of the surrounding velocity field using stereoscopic particle image velocimetry. The protrusion of the target particle, equipped with a force sensor, was systematically varied between zero and one-half diameter relative to the hexagonally packed adjacent spheres. Premultiplied spectra of drag force fluctuations were found to have bimodal shapes with a low-frequency (${\approx}0.5~\text{Hz}$) peak corresponding to the presence of very-large-scale motions (VLSMs) in the turbulent flow. The high-frequency ($\gtrapprox 4~\text{Hz}$) region of the drag force spectra cannot be explained by velocity time series extracted from points around the particle, but instead appears to be dominated by the action of pressure gradients in the overlying flow field. For small particle protrusions, this high-frequency region contributes a majority of the drag force variance, while the relative importance of the low-frequency drag force fluctuations increases with increasing protrusion. The amplitude of high-frequency drag force fluctuations is modulated by the VLSMs irrespective of particle protrusion. These results provide some insight into the mechanics of bed particle stability and indicate that the optimum conditions for particle entrainment may occur when a low-pressure region embedded in the high-velocity portion of a VLSM overlays a particle.

scholarly journals Towards harmonisation of image velocimetry techniques for river surface velocity observations

2020 ◽  
Vol 12 (3) ◽  
pp. 1545-1559 ◽  
Author(s):  
Matthew T. Perks ◽  
Silvano Fortunato Dal Sasso ◽  
Alexandre Hauet ◽  
Elizabeth Jamieson ◽  
Jérôme Le Coz ◽  
...  
Keyword(s):  
North America ◽  
Channel Flow ◽  
Large Scale ◽  
Open Channel ◽  
Reference Data ◽  
Accuracy Assessment ◽  
Open Channel Flow ◽  
Surface Velocity ◽  
Popular Approach ◽  
Image Velocimetry

Abstract. Since the turn of the 21st century, image-based velocimetry techniques have become an increasingly popular approach for determining open-channel flow in a range of hydrological settings across Europe and beyond. Simultaneously, a range of large-scale image velocimetry algorithms have been developed that are equipped with differing image pre-processing and analytical capabilities. Yet in operational hydrometry, these techniques are utilised by few competent authorities. Therefore, imagery collected for image velocimetry analysis (along with reference data) is required both to enable inter-comparisons between these differing approaches and to test their overall efficacy. Through benchmarking exercises, it will be possible to assess which approaches are best suited for a range of fluvial settings, and to focus future software developments. Here we collate and describe datasets acquired from seven countries across Europe and North America, consisting of videos that have been subjected to a range of pre-processing and image velocimetry analyses (Perks et al., 2020, https://doi.org/10.4121/uuid:014d56f7-06dd-49ad-a48c-2282ab10428e). Reference data are available for 12 of the 13 case studies presented, enabling these data to be used for reference and accuracy assessment.

Discussion of “Large-Scale Roughness in Open-Channel Flow”

1965 ◽  
Vol 91 (5) ◽  
pp. 242-262
Author(s):  
A. G. Mirajgaoker ◽  
Abhai K. Jain ◽  
John A. Roberson ◽  
E. M. O’Loughlin ◽  
K. K. Rao ◽  
...  
Keyword(s):  
Channel Flow ◽  
Large Scale ◽  
Open Channel ◽  
Open Channel Flow ◽  
Scale Roughness
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