scholarly journals Formation of Coherent Flow Structures beyond Vegetation Patches in Channel

Water ◽  
2021 ◽  
Vol 13 (20) ◽  
pp. 2812
Author(s):  
Masoud Kazem ◽  
Hossein Afzalimehr ◽  
Jueyi Sui
Keyword(s):  
Experimental Study ◽  
Considerable Effect ◽  
Middle Part ◽  
Vortex Structures ◽  
Flow Structures ◽  
Finite Width ◽  
Vegetation Patch ◽  
Weak Part ◽  
Side Flow ◽  
Vegetation Patches

By using model vegetation (e.g., synthetic bars), vortex structures in a channel with vegetation patches have been studied. It has been reported that vortex structures, including both the vertical and horizontal vortexes, may be produced in the wake in the channel bed with a finite-width vegetation patch. In the present experimental study, both velocity and TKE have been measured (via Acoustic Doppler Velocimeter—ADV) to study the formation of vortexes behind four vegetation patches in the channel bed. These vegetation patches have different dimensions, from the channel-bed fully covered patch to small-sized patches. Model vegetation used in this research is closely similar to vegetation in natural rivers with a gravel bed. The results show that, for a channel with a small patch (Lv/Dc = 0.44 and Dv/Dc = 0.33; where Lv and Dv are the length and width of patch and Dc is the channel width, respectively), both the flow passing through the patch and side flow around the patch have a considerable effect on the formation of flow structures beyond the patch. The results of further analysis via 3D classes of the bursting events show that the von Karman vortex street splits into two parts beyond the vegetation patch as the strong part near the surface and the weak part near the bed; while the middle part of the flow is completely occupied by the vertical vortex formed at a distance of 0.8–1 Hv beyond the vegetation patch, and thus, the horizontal vortexes cannot be detected in this region. The octant analysis is conducted for the coherent shear stress analysis that confirms the results of this experimental study.

Impacts of turbulent flow over a channel bed with a vegetation patch on the incipient motion of sediment

2018 ◽  
Vol 45 (9) ◽  
pp. 803-816
Author(s):  
Reza Shahmohammadi ◽  
Hossein Afzalimehr ◽  
Jueyi Sui
Keyword(s):  
Experimental Study ◽  
Reynolds Stress ◽  
Streamwise Velocity ◽  
Stress Pattern ◽  
Submerged Vegetation ◽  
Incipient Motion ◽  
Vegetation Patch ◽  
Motion Process ◽  
Velocity Turbulence ◽  
Vegetation Patches

In this experimental study, the effect of a submerged vegetation patch with individual plants on the incipient motion of sediment has been examined. Results showed that a vegetation patch in the channel bed affected the incipient motion process of sediment and resulted in significant impacts on flow velocity, turbulence intensities, turbulent kinetic energy, and Reynolds stress distribution. The presence of vegetation patches completely change vertical distribution of velocity and Reynolds stress pattern and leads to negative Reynolds stress values in zones with negative velocity gradient. In the presence of a vegetation patch, threshold cross-averaged streamwise velocity is 20% smaller than that without vegetation, but because of the occurrence of the preferential path around the sheath section, the near-bed streamwise velocity is the same as without vegetation. Also, vegetation increases turbulence intensity, thus encouraging sediment motion. In the presence of a vegetation patch, the Shields parameter is, on average, one and half times that of without vegetation over the bed.

Oscillatory Natural Convection of a Liquid Metal in Circular Cylinders

1994 ◽  
Vol 116 (3) ◽  
pp. 627-632 ◽  
Author(s):  
Y. Kamotani ◽  
F.-B. Weng ◽  
S. Ostrach ◽  
J. Platt
Keyword(s):  
Experimental Study ◽  
Natural Convection ◽  
Liquid Metal ◽  
Oscillatory Flow ◽  
Circular Cylinders ◽  
Flow Structures ◽  
Supercritical Flow ◽  
Aspect Ratios ◽  
Oscillation Frequencies ◽  
Rayleigh Numbers

An experimental study is made of natural convection oscillations in gallium melts enclosed by right circular cylinders with differentially heated end walls. Cases heated from below are examined for angles of inclination (φ) ranging from 0 deg (vertical) to 75 deg with aspect ratios Ar (height/diameter) of 2, 3, and 4. Temperature measurements are made along the circumference of the cylinder to detect the oscillations, from which the oscillatory flow structures are inferred. The critical Rayleigh numbers and oscillation frequencies are determined. For Ar=3 and φ = 0 deg, 30 deg the supercritical flow structures are discussed in detail.

An initial assessment of bed destabilization risk past vegetation patches using instrumented particles

2021 ◽  
Author(s):  
Yi Xu ◽  
Valyrakis Manousos ◽  
Panagiotis Michalis
Keyword(s):  
Initial Assessment ◽  
Flow Structures ◽  
Clear Water ◽  
Flow Conditions ◽  
Flow Parameters ◽  
Water Conditions ◽  
The Mean ◽  
Acoustic Doppler Velocimetry ◽  
Patch Density ◽  
Vegetation Patches

<p>Instream vegetation may alter the mean and turbukent flow fields leading to destabilizing riverbed surface, under certain flow conditions. In particular, recent research on instream vegetation hydrodynamics and ecohydrogeomorphology has focused on how energetic flow structures and bulk flow parameters downstream a vegetation may result in riverbed destabilization. This study, demonstrated the application of a 20mm novel instrumented particle in recording entrainment rates downstream simulated vegetation patches of distinct densities, at various distances downstream these. A patch of 6mm acrilic cylinders is used to simulate the emergent vegetation having the same diameter (12cm) and different porosities or densities (void volume equal to 1.25%, 3.15%, 6.25%, 11.25%, and 17.25%). The flow velocity near the instrumented particle is recorded using acoustic Doppler velocimetry (ADV) with appropriate seeding, under clear water conditions. Preliminary results are presented with focus on the effect of vegetation patch density on the flow field and subsequent effects on particle entrainment rates and implications for bed surface destabilisation.</p>

Experimental study of secondary vortex structures in a rotor wake

2019 ◽  
Vol 60 (11) ◽  
Author(s):  
C. Christian Wolf ◽  
Clemens Schwarz ◽  
Kurt Kaufmann ◽  
Anthony D. Gardner ◽  
Dirk Michaelis ◽  
...  
Keyword(s):  
Experimental Study ◽  
Vortex Structures ◽  
Secondary Vortex ◽  
Rotor Wake

scholarly journals Experimental study of coherent flow structures past a wall-mounted square cylinder

2019 ◽  
Vol 182 ◽  
pp. 137-146 ◽  
Author(s):  
Maria Ikhennicheu ◽  
Grégory Germain ◽  
Philippe Druault ◽  
Benoît Gaurier
Keyword(s):  
Experimental Study ◽  
Flow Structures ◽  
Square Cylinder ◽  
Coherent Flow Structures

Experimental Study on Integrated Performance for Flower Baffle Heat Exchanger’s Distance between Two Flower Baffles

2010 ◽  
Vol 29-32 ◽  
pp. 132-137 ◽  
Author(s):  
Xue Jiang Lai ◽  
Rui Li ◽  
Yong Dai ◽  
Su Yi Huang
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
The One ◽  
Integrated Performance ◽  
Quantity Of Heat ◽  
Side Flow ◽  
The Heat Transfer Coefficient

Flower baffle heat exchanger’s structure and design idea is introduced. Flower baffle heat exchanger has unique support structure. It can both enhance the efficiency of the heat transfer and reduce the pressure drop. Through the experimental study, under the same shell side flow, the heat transfer coefficient K which the distance between two flower baffles is 134mm is higher 3%~9% than the one of which the distances between two flower baffles are 163mm,123mm. The heat transfer coefficient K which the distance between two flower baffles is 147mm is close to the one of which the distances between two flower baffles is 134mm. The shell volume flow V is higher, the incremental quantity of heat transfer coefficient K is more. The integrated performance K/Δp of flower baffle heat exchanger which the distance between two flower baffles is 134mm is higher 3%~9% than the one of which the distances between two flower baffles are 163mm,123mm. Therefore, the best distance between two flower baffles exists between 134mm~147mm this experiment.

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