scholarly journals Comparison of flow turbulence over a sand bed and gravel bed channel

2021 ◽  
Author(s):  
Anurag Sharma ◽  
Bimlesh Kumar
Keyword(s):  
Reynolds Shear Stress ◽  
Longitudinal Velocity ◽  
Boundary Surface ◽  
Vertical Direction ◽  
Gravel Bed ◽  
Flow Energy ◽  
Bed Materials ◽  
Flow Turbulence ◽  
Sand And Gravel ◽  
Flow Anisotropy

Abstract Experiments were performed to examine the variations in flow turbulence with respect to sand and gravel bed channel. The 3D instantaneous velocity of water is measured by acoustic doppler velocimeter (ADV) at the test section which will provide an important data related to the flow turbulence. The parameters of turbulence measured that the vertical profiles of longitudinal velocity in flows with sand bed channel at the vicinity of bed surface are higher by 2–6% than flow subjected to gravel bed channel, while away from the boundary surface, it decreases by 5–10%. The variations of Reynolds shear stress increases by 35–50% with gravel bed channel, indicating higher exchange of flow energy towards the boundary and vice versa. The higher value is obtained for shear velocities by 58.5% and the von Karman's constant with gravel bed channel. The gravel bed channel influenced the turbulence intensities with higher magnitude in the streamwise and vertical direction. The present study also analysed the flow anisotropy, correlations coefficient and turbulence diffusivity and compared the results. The outcomes of the current work are beneficial for civil and hydraulic engineers, since the data of turbulence will advance the management of bed materials present in the river.

Model Tests on Additional Stress Transmission between Different Granular Materials in Foundation Soils

2014 ◽  
Vol 919-921 ◽  
pp. 828-834
Author(s):  
Chang Dan Wang ◽  
Shun Hua Zhou ◽  
Hui Su
Keyword(s):  
Granular Materials ◽  
Boundary Surface ◽  
Vertical Direction ◽  
Stress Transfer ◽  
Fine Sand ◽  
Compression Modulus ◽  
Model Tests ◽  
Additional Stress ◽  
Stress Transmission ◽  
Different Soils

To research and analyze the additional stress distribution and change of granular materials, the model tests are used to observe vertical additional stress in different position and depth in different foundations. And the comparison between observed values both in different soils and single soils is conducted to analyze the transmission and attenuation of additional stress in granular materials. The research results show that the existing of boundary surface can lead to different vertical additional stress transmit obviously. And with the increasing of loading, the vertical additional stress differences between that of different soils get larger, meanwhile, the ratio of stress differences to smaller additional stress increases slightly. With the increasing of depth, the attenuation rate of vertical additional stress of silty soil changes much fast than that of fine sand. Wherever in horizontal direction or vertical direction, the vertical additional stress of fine sand which has higher compression modulus in different soils is slightly larger than that in single soil and transfers additional stress (loading) more under the same loading. To granular materials, inner friction structure effect is evident influence to additional stress transfer.

scholarly journals The Effect of Habitat Structure Boulder Spacing on Near-Bed Shear Stress and Turbulent Events in a Gravel Bed Channel

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1423
Author(s):  
Amir Golpira ◽  
Fengbin Huang ◽  
Abul B.M. Baki
Keyword(s):  
Shear Stress ◽  
Habitat Structure ◽  
Open Channel ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Quadrant Analysis ◽  
Bed Shear Stress ◽  
Gravel Bed ◽  
Restoration Practices ◽  
Ejections And Sweeps

This study experimentally investigated the effect of boulder spacing and boulder submergence ratio on the near-bed shear stress in a single array of boulders in a gravel bed open channel flume. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components. Four methods of estimating near-bed shear stress were compared. The results suggested a significant effect of boulder spacing and boulder submergence ratio on the near-bed shear stress estimations and their spatial distributions. It was found that at unsubmerged condition, the turbulent kinetic energy (TKE) and modified TKE methods can be used interchangeably to estimate the near-bed shear stress. At both submerged and unsubmerged conditions, the Reynolds method performed differently from the other point-methods. Moreover, a quadrant analysis was performed to examine the turbulent events and their contribution to the near-bed Reynolds shear stress with the effect of boulder spacing. Generally, the burst events (ejections and sweeps) were reduced in the presence of boulders. This study may improve the understanding of the effect of the boulder spacing and boulder submergence ratio on the near-bed shear stress estimations of stream restoration practices.

Measurements in an Axisymmetric Turbulent Boundary Layer Along a Circular Cylinder

1976 ◽  
Vol 27 (3) ◽  
pp. 217-228 ◽  
Author(s):  
Noor Afzal ◽  
K P Singh
Keyword(s):  
Boundary Layer ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Constant Pressure ◽  
Reynolds Shear Stress ◽  
Longitudinal Velocity ◽  
Outer Region ◽  
Wall Region ◽  
Mean Velocity ◽  
Dimensional Boundary

SummaryIn an axisymmetric turbulent boundary layer along a circular cylinder at constant pressure, measurements have been made of mean velocity profile and turbulence characteristics: longitudinal velocity fluctuations, Reynolds shear stress, transverse correlation and spectrum. It has been found that the qualitative behaviour of an axisymmetric turbulent boundary layer is similar to that of a two-dimensional boundary layer in the wall region, where as in the outer region the effects of transverse curvature are observed.

Direct Numerical Simulation of Heated Turbulent Pipe Flow at Supercritical Pressure

2016 ◽  
Vol 2 (3) ◽  
Author(s):  
Xu Chu ◽  
Eckart Laurien
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Forced Convection ◽  
Reynolds Shear Stress ◽  
Streamwise Velocity ◽  
Supercritical Pressure ◽  
Turbulent Pipe Flow ◽  
Working Fluid ◽  
Convection Flow ◽  
Flow Turbulence

For fluids at supercritical pressure, the phase change from liquid to gas does not exist. Meanwhile, the fluid properties change drastically in a narrow temperature range. With supercritical fluid as working fluid in a heated pipe, heat-transfer deterioration and recovery have been observed, which corresponds to the turbulent flow relaminarization and recovery. Direct numerical simulation (DNS) of supercritical carbon dioxide flow in a heated vertical circular pipe is developed with the open-source code OpenFOAM in this study. Forced-convection and mixed-convection cases including upward and downward flow have been considered in the simulation. In the forced convection, flow turbulence is attenuated due to acceleration from thermal expansion, which leads to a peak of the wall temperature. However, buoyancy shows a stronger impact on the flow. In the upward flow, the average streamwise velocity distribution turns into an M-shaped profile because of the external effect of buoyancy. Besides that, negative buoyancy production caused by the density variation reduces the Reynolds shear stress to almost zero, which means that the flow is relaminarized. Further downstream, turbulence is recovered. This behavior of flow turbulence is confirmed by visualization of turbulent streaks and vortex structures.

scholarly journals A Comparative Study between Sand- and Gravel-Bed Open Channel Flows in the Wake Region of a Bed-Mounted Horizontal Cylinder

Fluids ◽  
2021 ◽  
Vol 6 (7) ◽  
pp. 239
Author(s):  
Kalpana Devi ◽  
Prashanth Reddy Hanmaiahgari ◽  
Ram Balachandar ◽  
Jaan H. Pu
Keyword(s):  
Comparative Study ◽  
Flow Velocity ◽  
Normal Stress ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Horizontal Cylinder ◽  
Wake Region ◽  
Gravel Bed ◽  
Rough Bed ◽  
Bed Roughness

In nature, environmental and geophysical flows frequently encounter submerged cylindrical bodies on a rough bed. The flows around the cylindrical bodies on the rough bed are very complicated as the flow field in these cases will be a function of bed roughness apart from the diameter of the cylinder and the flow velocity. In addition, the sand-bed roughness has different effects on the flow compared to the gravel-bed roughness due to differences in the roughness heights. Therefore, the main objective of this article is to compare the mean velocities and turbulent flow properties in the wake region of a horizontal bed-mounted cylinder over the sand-bed with that over the gravel-bed. Three experimental runs, two for the sand-bed and one for the gravel-bed with similar physical and hydraulic conditions, were recorded to fulfil this purpose. The Acoustic Doppler Velocimetry (ADV) probe was used for measuring the three-dimensional (3D) instantaneous velocity data. This comparative study shows that the magnitude of mean streamwise flow velocity, streamwise Reynolds normal stress, and Reynolds shear stress are reduced on the gravel-bed compared to the sand-bed. Conversely, the vertical velocities and vertical Reynolds normal stress are higher on the gravel-bed than the sand-bed.

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