scholarly journals Investigation of the Effect of Vegetation on Flow Structures and Turbulence Anisotropy around Semi-Elliptical Abutment

Water ◽  
2021 ◽  
Vol 13 (21) ◽  
pp. 3108
Author(s):  
Seyedeh Fatemeh Nabaei ◽  
Hossein Afzalimehr ◽  
Jueyi Sui ◽  
Bimlesh Kumar ◽  
Seyed Hamidreza Nabaei
Keyword(s):  
Reynolds Shear Stress ◽  
Azimuthal Angle ◽  
Flow Structures ◽  
Wake Vortex ◽  
Primary Vortex ◽  
Turbulence Anisotropy ◽  
Bridge Abutment ◽  
Turbulent Statistics ◽  
Scour Hole ◽  
Profile Changes

In the present experimental study, the effect of vegetation on flow structure and scour profile around a bridge abutment has been investigated. The vegetation in the channel bed significantly impacted the turbulent statistics and turbulence anisotropy. Interestingly, compared to the channel without vegetation, the presence of vegetation in the channel bed dramatically reduced the primary vortex, but less impacts the wake vortex. Moreover, the tangential and radial velocities decreased with the vegetation in the channel bed, while the vertical velocity (azimuthal angle > 90°) had large positive values near the scour hole bed. Results showed that the presence of the vegetation in the channel bed caused a noticeable decrease in the Reynolds shear stress. Analysis of the Reynolds stress anisotropy indicated that the flow had more tendency to be isotropic for the vegetated bed. Results have shown that the anisotropy profile changes from pancake-shaped to cigar-shaped in the un-vegetated channel. In contrast, it had the opposite reaction for the vegetated bed.

Turbulent Statistics of Rarefield Flows in Microchannel Flow and Heat Transfer

2004 ◽  
Author(s):  
G. X. Li ◽  
W. Q. Tao ◽  
Z. Y. Li ◽  
B. Yu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Shear Stress ◽  
Reynolds Shear Stress ◽  
Wall Region ◽  
Turbulent Heat ◽  
Time Step ◽  
Temperature Variance ◽  
Flow And Heat Transfer ◽  
Turbulent Statistics

Direct numerical simulation has been carried out to investigate the effect of weak rarefaction on turbulent gas flow and heat transfer characteristics in mirochannel. The Reynolds number based on the friction velocity and the channel half width is 150. Grid number is 64×128×64. Fractional time step method is employed for the unsteady Navier-Stokes equations, and the governing equations are discretized with Finite Difference Method. Statistical quantities such as turbulent intensity, Reynolds shear stress, turbulent heat flux and temperature variance are obtained under various Knudsen number from 0 to 0.05. The results show that rarefaction can influence the turbulent flow and heat transfer statistics. The streamwise mean velocity and temperature increase with increase of Kn number. In the near wall region rarefaction can increase the turbulent intensities and temperature variance. The effect of rarefaction on Reynolds shear stress and wall-normal heat flux are presented. The instantaneous velocity fluctuations in the vicinity of the wall are visualized and the influence of Kn number on the flow structure is discussed.

PIV Study of Adverse and Favorable Pressure Gradient Turbulent Flows Over Transverse Ribs

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
M. Agelinchaab ◽  
M. F. Tachie
Keyword(s):  
Pressure Gradient ◽  
Turbulent Flows ◽  
Reynolds Shear Stress ◽  
Adverse Pressure Gradient ◽  
Bottom Wall ◽  
Combined Effects ◽  
Mean Flow ◽  
Turbulent Statistics ◽  
Favorable Pressure Gradient ◽  
The Mean

This paper reports an experimental study of the combined effects of rib roughness and pressure gradient on turbulent flows produced in asymmetric converging and diverging channels. Transverse square ribs with pitch-to-height ratio of 4 were attached to the bottom wall of the channel to produce the rib roughness. A particle image velocimetry technique was used to conduct measurements at several streamwise-transverse planes located upstream, within, and downstream of the converging and diverging sections of the channel. From these measurements, the mean velocities and turbulent statistics at the top plane of the ribs and across the channel were obtained. The data revealed non-negligible wall-normal motion and interaction between the cavities and overlying boundary layers. The different drag characteristics of the rough bottom wall and the smooth top wall produced asymmetric distributions of mean velocity and turbulent statistics across the channel. The asymmetry of these profiles is most extreme in the presence of adverse pressure gradient. Because of the manner in which pressure gradient modifies the mean flow and turbulence production, it was found that the streamwise turbulence intensity and Reynolds shear stress in the vicinity of the ribs are lower in the adverse pressure gradient than in the favorable pressure gradient channel. The results show also that the combined effects of rib roughness and adverse pressure gradient on the turbulent intensity statistics are significantly higher than when roughness and adverse pressure gradient are applied in isolation.

scholarly journals Experimental Investigation of Flow Structures Around side-by-side Yawed Cylinders in Shallow Water

2019 ◽  
Vol 2 (3) ◽  
pp. 1138-1151
Author(s):  
Ebubekir Kütük ◽  
Umutcan Olmuş ◽  
Tahir Durhasan ◽  
Hüseyin Akıllı
Keyword(s):  
Shear Stress ◽  
Shallow Water ◽  
Vector Fields ◽  
Particle Image ◽  
Reynolds Shear Stress ◽  
Flow Structures ◽  
Piv Technique ◽  
Gap Ratio ◽  
Image Velocimetry ◽  
Yaw Angle

The aim of this experimental study is to investigate the flow behaviour around two equally yawed side-by-side cylinders in shallow water. Time averaged velocity vector fields, Reynolds shear stress distrubutions and streamline patterns were obtained using Particle Image Velocimetry (PIV) technique. The gap ratio between the cylinders were in the range of G/D=0.25-1.25 with an increment of 0.25 where G is the distance between the cylinders and D is the cylinder diameter. Five different yaw angles of cylinders were employed during the experiment. The results showed that the yaw angle, α had an important effect on the flow structures of the downstream of the cylinders. Reynolds shear stress and vortex structures were decreased, the intensity of the jet like flow were significantly attenuated for the gap ratios of G/D=0.25, 0.50 and 0.75.

scholarly journals Effect of L-shaped slots on scour around a bridge abutment

2021 ◽  
Author(s):  
Neveen Y. Saad ◽  
Ehab M. Fattouh ◽  
M. Mokhtar
Keyword(s):  
Laboratory Experiments ◽  
Vertical Wall ◽  
Clear Water ◽  
Flow Conditions ◽  
Bridge Abutment ◽  
Scour Hole ◽  
Bed Materials ◽  
Bridge Failure ◽  
Study Laboratory ◽  
Area And Volume

Abstract Local scour is the most significant cause of bridge failure. Providing a short abutment with a straight slot has proved to be an effective method for reducing scour at this abutment. In this study, laboratory experiments have been conducted to investigate the effectiveness of using L-shaped slots in comparison to the commonly used straight slot, on the scour reduction at short vertical-wall abutment under clear-water flow conditions and uniform bed materials. The slots were just above the bed and their diameters equal to half the abutment's length. The results illustrated that it is essential to have a straight slot in any combination of slots, as any configuration without one is inefficient. Also, a combination of a straight slot with one side slot in the middle of the abutment's width gives better performance than an individual straight slot, as it reduces the depth, area, and volume of the scour hole by about 32.6, 26.8, and 43.6% respectively, in comparison to 23.2, 20.7, and 35.3% for the straight slot alone.

Measurements of Turbulent Transport in a Square Channel with One Ribbed Wall

2022 ◽  
Author(s):  
Sebastian Ruck ◽  
Frederik Arbeiter
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Shear Layer ◽  
Reynolds Shear Stress ◽  
Turbulent Transport ◽  
Reynolds Numbers ◽  
Flow Structures ◽  
Channel Height ◽  
Height Ratio ◽  
Square Channel

Abstract The velocity field of the fully developed turbulent flow in a one-sided ribbed square channel (rib-height-to-channel-height ratio of k/h = 0.0667, rib-pitch-to-rib-height ratio of p/k = 9) were measured at Reynolds numbers (based on the channel height h and the mean bulk velocity uB) of Reh = 50 000 and 100 000 by means of Laser-Doppler-Anemometry (LDA). Triple velocity correlations differed slightly between both Reynolds numbers when normalized by the bulk velocity and the channel height, similarly to the first- and second-order statistical moments of the velocity. Their near-wall behavior reflected the crucial role of turbulent transport near the rib crest and within the separated shear layer. Sweep events occurred with the elongated flow structures of the flapping shear layer and gained in importance towards the channel bottom wall, while strong ejection events near the rib leading and trailing edges coincided with flow structures bursting away from the wall. Despite the predominant occurrence of sweep events close to the ribbed wall within the inter-rib spacing, ejection events contributed with higher intensity to the Reynolds shear stress. Ejection and sweep events and their underlying transport phenomena contributing to the Reynolds shear stress were almost Reynolds number-insensitive in the resolved flow range. The invariance to the Reynolds number can be of benefit for the use of scale-resolving simulation methods in the design process of rib structures for heat exchange applications.

Turbulent flow field in a scour hole at a semicircular abutment

2005 ◽  
Vol 32 (1) ◽  
pp. 213-232 ◽  
Author(s):  
Subhasish Dey ◽  
Abdul Karim Barbhuiya
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Primary Vortex ◽  
Scour Hole ◽  
Turbulent Flow Field ◽  
Development And Validation ◽  
Bed Shear Stresses

The three-dimensional turbulent flow field in a scour hole at a semicircular abutment under a clear water regime was experimentally measured in a laboratory flume using an acoustic Doppler velocimeter. The distributions of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy, and Reynolds stresses at different azimuthal planes are presented. Upstream, presentation of flow field through vector plots at azimuthal and horizontal planes shows the existence of a large primary vortex associated with the downflow inside the scour hole. On the other hand, downstream, the flow field is irregular. The bed shear stresses are determined from the Reynolds stresses and velocity gradients. The data presented in this paper would be useful for the development and validation of flow field models, which can be used to determine the strength of the primary vortex that is used to estimate scour depth at bridge abutments.Key words: bridge abutments, fluid flow, three-dimensional flow, turbulent flow, open channel flow, scour, sediment transport, hydraulic engineering.

scholarly journals Velocity and Turbulent flow field at around the cylindrical Pier

2020 ◽  
Vol 9 (4) ◽  
pp. 534-548
Keyword(s):  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Flow Behaviour ◽  
Acoustic Doppler Velocimeter ◽  
Wake Region ◽  
Velocity Data ◽  
Clear Water ◽  
Control Structures ◽  
Upstream Side ◽  
Scour Hole

This experimental study shows the velocity and turbulence field at vicinity of cylindrical pier with scour hole under clear water condition. The three dimensional velocity data were obtained at 5 cm, 10 cm, 20 cm and 30 cm from the pier with use of Acoustic Doppler Velocimeter at 360 degrees around the pier with 30-degree interval. The flow behaviour were extensively analyzed with the help of time averaged normalized velocity, Turbulent intensity, Turbulent kinetic energy and Reynolds shear stress plots. The study shows the flow behaviour at inside the scour hole, at scour hole ring and outside the scour hole which gives the elusive view of flow at vicinity of pier. An upstream side pier, the flow behaviour almost follows the similar trend but behind a cylinder the flow is asymmetry due to wake vortex and vortex shedding found at the wake region. This study offers an ample cognizance of flow structure at vicinity of circular pier, which is essential in order to design an effective scour control structures like rip-rap, W weir, vanes, slot and etc.,

Separated-Flow Transition: Part 2 — Experimental Results

1998 ◽  
Author(s):  
Anca Hatman ◽  
Ting Wang
Keyword(s):  
Reynolds Shear Stress ◽  
Separated Flow ◽  
Adverse Pressure Gradient ◽  
Transition Process ◽  
Flow Structures ◽  
Flow Transition ◽  
Pressure Gradients ◽  
Hot Wire ◽  
Bubble Bursting ◽  
Transition Mechanism

The present paper focuses on presenting the results of the experimental investigation of the transition process in separated boundary layers on a flat plate at zero incidence, with imposed adverse pressure gradients. The combined effects of Reynolds number and adverse pressure gradient strength on the transition mechanism, bubble geometry, and bubble bursting process are studied. The flow structures and the unsteady aspects associated with separated-flow transition are analyzed for three representative experimental cases. Surface pressure results and detailed boundary layer measurements using hot-wire anemometry are presented as mean and rms velocity profiles, and Reynolds shear stress distribution. Turbulent intermittency and spectral analysis results are briefly introduced.

scholarly journals THREE DIMENSIONAL FLOW STRUCTURES AROUND A DEEP SCOUR HOLE

2018 ◽  
Vol 40 ◽  
pp. 03015
Author(s):  
Akihiro Tominaga ◽  
Naohiko Sassa ◽  
Yuji Hara ◽  
Yuka Kuno
Keyword(s):  
Field Observation ◽  
River Discharge ◽  
Large Scale ◽  
Three Dimensional ◽  
Flow Structures ◽  
3D Flow ◽  
Three Dimensional Flow ◽  
Model Experiments ◽  
Dimensional Flow ◽  
Scour Hole

The existence of a planform vortex is considered to be the cause of development and sustention of large-scale local scouring in the Kiso River. In order to make clear the 3D flow structures in this deep local scour, we conducted a field observation and model experiments. From the result of ADCP set on the bottom of the scour hole, the velocity in the hole was increasing and the vertical vortex was developing, with an increase of river discharge. It is indicated that considerable magnitude of velocity was generated even near the bottom by the action of vertical vortex. This vortex was recognized in the model experiments. Consequently, the vertical vortex contributes to develop and maintain the large-scale local scouring.

Flow and Dispersion Characteristics of a Stack-Issued Backward Inclined Jet in Crossflow

2016 ◽  
Vol 33 (6) ◽  
pp. 841-852 ◽  
Author(s):  
M. G. Khouygani ◽  
R.-F. Huang ◽  
C.-M. Hsu
Keyword(s):  
Shear Layer ◽  
Inclination Angle ◽  
Flow Characteristics ◽  
Flux Ratio ◽  
Wake Flow ◽  
Flow Structures ◽  
Wake Vortex ◽  
Near Wake ◽  
Jet In Crossflow ◽  
Inclination Angles

AbstractThe effects of backward inclination angle on flow characteristics and jet dispersion properties of a stack-issued jet in crossflow were studied by means of instantaneous and long-exposure photography, particle image velocimetry (PIV), and tracer-gas concentration detections at a Reynolds number of 2,400, a jet-to-crossflow momentum flux ratio of 1.0, and the backward inclination angles θ = 0° - 60°. Three characteristic flow patterns featured by different near-wake flow structures were found within the surveyed span of the backward inclination angle: low (θ ≤ 25°), mediate (25° < θ < 50°), and high (θ ≥ 50°). In the range of low backward inclination angle, mushroom vortices appeared in the upwind shear layer. Jet fluids were entrained into the jet- and tube-wakes because the near wake region was characterized by a jet-wake vortex and a downwash flow. In the range of mediate backward inclination angle, forward-rolling vortices were formed in the upwind shear layer. Jet fluids were entrained into the jet wake but not appearing in the tube wake because the near wake was characterized by an isolated tube wake and up-going flows. In the range of high backward inclination angle, small-sized forward-rolling vortices were observed in the upwind shear layer. Jet fluids were not observed in both the jet- and tube-wakes because all flows went forward without reversal or vortex, which was similar to that in a jet in co-flow. Large turbulence intensities occurred around the jet-wake vortex and along sides of the tube wake bifurcation line, therefore the mixing at the low backward inclination angles presented better properties than those at mediate and high backward inclination angles owing to the featured flow structures and turbulence intensities.

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