Turbulent Flow through Random Vegetation on a Rough Bed

River vegetation radically modifies the flow field and turbulence characteristics. To analyze the vegetation effects on the flow, most scientific studies are based on laboratory tests or numerical simulations with vegetation stems on smooth beds. Nevertheless, in this manner, the effects of bed sediments are neglected. The aim of this paper is to experimentally investigate the effects of bed sediments in a vegetated channel and, in consideration of that, comparative experiments of velocity measures, performed with an Acoustic Doppler Velocimeter (ADV) profiler, were carried out in a laboratory flume with different uniform bed sediment sizes and the same pattern of randomly arranged emergent rigid vegetation. To better comprehend the time-averaged flow conditions, the time-averaged velocity was explored. Subsequently, the analysis was focused on the energetic characteristics of the flow field with the determination of the Turbulent Kinetic Energy (TKE) and its components, as well as of the energy spectra of the velocity components immediately downstream of a vegetation element. The results show that both the vegetation and bed roughness surface deeply affect the turbulence characteristics. Furthermore, it was revealed that the roughness influence becomes predominant as the grain size becomes larger.

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Determination of the Flow Field in LP Steam Turbines

Volume 1: Turbomachinery ◽

10.1115/86-gt-210 ◽

1986 ◽

Author(s):

J. Wachter ◽

G. Eyb

Keyword(s):

Flow Field ◽

Measuring Equipment ◽

Short Description ◽

Test Stand ◽

Steam Turbines ◽

Flow Conditions ◽

Flow Measurements ◽

Last Stage ◽

The University

Up to now the determination of flow conditions across the entire circumference in LP steam turbines appears to be a difficult undertaking. The difficulties are mainly caused by the condensing medium steam and by the limited access to the stage from outside. The Last Stage Test Stand at the University of Stuttgart is a suitable facility for flow measurements in the LP part of steam turbines. Besides a short description of the test stand itself, the measuring equipment and the newly developed methods for data acquisition and evaluation are presented. Finally the flow field behind the last stage is shown and the results interpreted.

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Bed Roughness Effects on the Turbulence Characteristics of Flows through Emergent Rigid Vegetation

Water ◽

10.3390/w12092401 ◽

2020 ◽

Vol 12 (9) ◽

pp. 2401 ◽

Cited By ~ 3

Author(s):

Nadia Penna ◽

Francesco Coscarella ◽

Antonino D’Ippolito ◽

Roberto Gaudio

Keyword(s):

Shear Stress ◽

Reynolds Shear Stress ◽

Surface Region ◽

Shear Stresses ◽

Stress Distributions ◽

Flow Zone ◽

Roughness Effects ◽

Bed Sediments ◽

Turbulence Characteristics ◽

Bed Roughness

During floods, the riparian vegetation in a watercourse significantly changes the velocity distribution and the turbulence structures of the flow. However, a certain influence on them is always exerted by the bed sediments. The aim of the present work is to study the bed roughness effects on the turbulence characteristics in an open-channel flow with rigid and emergent vegetation. Toward this end, an experimental campaign was conducted and consisted of three runs with different bed roughness conditions. The study is based on the analysis of the velocity, Reynolds shear stress, and viscous stress distributions. The results show that, in the region below the free surface region, the flow is strongly influenced by the vegetation. However, moving toward the bed, the flow is affected by a combined effect of vegetation, firstly, and bed roughness, secondly. This flow zone becomes more extended, as the size of the bed sediments increases. The shear stress distributions confirm the distinction between the two flow regions. In fact, the shear stresses are practically negligible in the upper zone of the water depth influenced by vegetation, whereas, owing to the bed roughness, they reach the maximum value near the bed surface. Finally, the analysis of the turbulent kinetic energy (TKE) revealed high values below the crest level and in the near-bed flow zone in the streamwise direction, whereas a strong lateral variation of TKE from the flume centerline to the cylinder occurred in the intermediate region.

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Immobilized Luminescent Bacteria for the Detection of Mycotoxins under Discrete and Flow-Through Conditions

Biosensors ◽

10.3390/bios9020063 ◽

2019 ◽

Vol 9 (2) ◽

pp. 63 ◽

Cited By ~ 3

Author(s):

Olga Senko ◽

Nikolay Stepanov ◽

Olga Maslova ◽

Rashid Akhundov ◽

Anvar Ismailov ◽

...

Keyword(s):

Aqueous Media ◽

Photobacterium Phosphoreum ◽

Poly Vinyl Alcohol ◽

Bacterial Cells ◽

Flow Conditions ◽

Luminescent Bacteria ◽

Wide Range ◽

Order Of Magnitude ◽

Flow Through

A biosensitive element in the form of bacterial Photobacterium phosphoreum cells immobilized in poly(vinyl alcohol) cryogel was tested for the determination of different mycotoxins under discrete and flow-through analysis conditions. The immobilized bioluminescent cells made it possible to quantify the presence of Ochratoxin A, Sterigmatocystin, Zearalenone, and Deoxynivalenon in aqueous media in a wide range of their concentrations (0.017–56 mg/L, 0.010–33 mg/L, 0.009–14 mg/L, and 0.026–177 mg/L, respectively) via measuring the quenching of cell luminescence. The flow conditions allowed the analysis sensitivity to be improved by an order of magnitude in terms of detected concentrations. Using the immobilized luminescent bacterial cells, we have shown the possibility of evaluating the efficiency of the mycotoxins’ hydrolysis under the action of enzymes. In this way, a 94 ± 4.5% efficiency of Zearalenone hydrolysis with hexahistidine-containing organophosphorus hydrolase for 1h-long treatment of the mycotoxin solution (100 mg/L) was shown.

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DRAG COEFFICIENT OF VEGETATION IN FLOW MODELING

Coastal Engineering Proceedings ◽

10.9753/icce.v33.posters.4 ◽

2012 ◽

Vol 1 (33) ◽

pp. 4

Author(s):

Zhan Hu ◽

M. Stive ◽

T. Zitman ◽

T. Suzuki

Keyword(s):

Drag Coefficient ◽

Numerical Models ◽

Flow Conditions ◽

Mean Velocity ◽

Local Flow ◽

Rigid Vegetation ◽

Flow Through ◽

The Mean ◽

Empirical Coefficients

Flow through vegetation has a significant impact on sediment transport and ecosystem robustness in the coastal and fluvial environment. Numerical models (Nepf and Vivoni, 2000; Uittenbogaaard, 2003) have been developed to simulate this type of flow. The success of these models depends on proper characterization of the main processes and appropriate setting of pre-defined empirical coefficients. Among others, the drag coefficient CD is one of the most important coefficients, which influences the mean velocity and the turbulence characteristics (Nepf and Ghisalberti, 2008). Tanino and Nepf (2008) and Cheng (2011) have derived empirical relationships of CD for flow through emerged rigid vegetation. Both studies confirm that CD is related to canopy properties (plants density, diameter, etc.) as well as flow conditions. However, in both studies CD is estimated by simply equating the vegetation drag force to the water level gradient. Bed shear stress and Reynolds stress were ignored. More importantly, the CD provided by these expressions is depth averaged, which is not suitable for modelling flow and canopy that both vary in vertical (Nepf and Vivoni, 2000). In this study, the CD relation proposed by Cheng (2011) is modified. This new relation depends on the local flow conditions and canopy properties in the vertical. Further, this relation is implemented in an iterative scheme of a 1DV flow model. The modelling results are compared with experiment data of flow through emerged and submerged rigid vegetation. Our results show that when special defined Reynolds number is small, this relation performs less well compare to that when it is larger.

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Roughness effects on turbulence characteristics in an open channel flow

Canadian Journal of Civil Engineering ◽

10.1139/l10-098 ◽

2010 ◽

Vol 37 (12) ◽

pp. 1600-1612 ◽

Cited By ~ 1

Author(s):

Md Abdullah Al Faruque ◽

Ram Balachandar

Keyword(s):

Open Channel ◽

Reynolds Shear Stress ◽

Quadrant Analysis ◽

Roughness Effects ◽

Turbulence Characteristics ◽

Rough Bed ◽

Median Diameter ◽

Specific Geometry ◽

Bed Roughness ◽

Rough Beds

A comprehensive study was carried out to understand the effect of roughness on the turbulence characteristics of flow in an open channel. To this end, tests were conducted with four different types of bed surface conditions at two different Reynolds number (Re = 47 500 and 31 000). This includes the use of an impermeable smooth bed, impermeable rough bed, permeable sand bed, and an impermeable bed with distributed roughness. The roughness is generated using sand grains of median diameter 2.46 mm. The effect of bed roughness is seen to have penetrated through most of the flow depth, disputing the conventional "wall similarity" hypothesis. The results show that the distributed roughness generates the largest roughness effect. The differences in the characteristics as noted by the velocity triple products exceed 200% between the flow over the smooth and rough beds. Although the same sand grain is used to create the different rough bed conditions, there are differences in turbulence characteristics, which is an indication that specific geometry of the roughness has an influence. A quadrant analysis indicates that roughness increases the contribution of the extreme turbulent events that produce very large instantaneous Reynolds shear stress and consequently influence the flow.

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Geotextiles. Test method for the determination of the filtration behaviour of geotextiles under turbulent water flow conditions

10.3403/30197695 ◽

2013 ◽

Keyword(s):

Water Flow ◽

Test Method ◽

Flow Conditions ◽

Turbulent Water

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Simultaneous Determination of Antidiabetic Thiazolidinediones Using Flow Through Voltammetric Sensor

Current Pharmaceutical Analysis ◽

10.2174/1573412910666140818215811 ◽

2014 ◽

Vol 10 (4) ◽

pp. 239-245 ◽

Cited By ~ 1

Author(s):

Lai-Hao Wang ◽

Yan-Lin Song

Keyword(s):

Simultaneous Determination ◽

Voltammetric Sensor ◽

Flow Through

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Spectroscopic Techniques versus Pitot Tube for the Measurement of Flow Velocity in Narrow Ducts

Sensors ◽

10.3390/s20247349 ◽

2020 ◽

Vol 20 (24) ◽

pp. 7349

Author(s):

Francesco D’Amato ◽

Silvia Viciani ◽

Alessio Montori ◽

Marco Barucci ◽

Carmen Morreale ◽

...

Keyword(s):

Flow Field ◽

Flow Velocity ◽

Pitot Tube ◽

Optical Measurements ◽

Trace Gas ◽

Dual Function ◽

Spectroscopic Techniques ◽

Gas Composition ◽

Flow Conditions ◽

Theoretical Simulation

In order to assess the limits and applicability of Pitot tubes for the measurement of flow velocity in narrow ducts, e.g., biomass burning plants, an optical, dual function device was implemented. This sensor, based on spectroscopic techniques, targets a trace gas, injected inside the stack either in bursts, or continuously, so performing transit time or dilution measurements. A comparison of the two optical techniques with respect to Pitot readings was carried out in different flow conditions (speed, temperature, gas composition). The results of the two optical measurements are in agreement with each other and fit quite well the theoretical simulation of the flow field, while the results of the Pitot measurements show a remarkable dependence on position and inclination of the Pitot tube with respect to the duct axis. The implications for the metrology of small combustors’ emissions are outlined.

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