An analysis of the characteristics of rough bed turbulent shear stresses in an open channel

1997 ◽  
Vol 11 (3) ◽  
pp. 193-210 ◽  
Author(s):  
A. Keshavarzy ◽  
J. E. Ball
Keyword(s):  
Open Channel ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Rough Bed

scholarly journals Turbulence structure of non-uniform rough open channel flow

2018 ◽  
Vol 40 ◽  
pp. 05039
Author(s):  
Priscilla Williams ◽  
Vesselina Roussinova ◽  
Ram Balachandar
Keyword(s):  
Pressure Gradient ◽  
Channel Flow ◽  
Friction Velocity ◽  
Open Channel ◽  
Open Channel Flow ◽  
Shear Stresses ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Rough Bed ◽  
The Mean

This paper focuses on the turbulence structure in a non-uniform, gradually varied, sub-critical open channel flow (OCF) on a rough bed. The flow field is analysed under accelerating, near-uniform and decelerating conditions. Information for the flow and turbulence parameters was obtained at multiple sections and planes using two different techniques: two-component laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). Different outer region velocity scaling methods were explored for evaluation of the local friction velocity. Analysis of the mean velocity profiles showed that the overlap layer exists for all flow cases. The outer layer of the decelerated velocity profile was strongly affected by the pressure gradient, where a large wake was noted. Due to the prevailing nature of the experimental setup it was found that the time-averaged flow quantities do not attained equilibrium conditions and the flow is spatially heterogeneous. The roughness generally increases the friction velocity and its effect was stronger than the effect of the pressure gradient. It was found that for the decelerated flow section over a rough bed, the mean flow and turbulence intensities were affected throughout the flow depth. The flow features presented in this study can be used to develop a model for simulating flow over a block ramp. The effect of the non-uniformity and roughness on turbulence intensities and Reynolds shear stresses was further investigated.

scholarly journals A Meshless WCSPH Boundary Treatment for Open-Channel Flow over Small-Scale Rough Bed

2019 ◽  
Vol 2019 ◽  
pp. 1-17
Author(s):  
Yang Shi ◽  
Jiahua Wei ◽  
Shaowu Li ◽  
Peng Song ◽  
Bangwen Zhang
Keyword(s):  
Channel Flow ◽  
Open Channel ◽  
Polynomial Regression ◽  
Open Channel Flow ◽  
Turbulent Shear ◽  
Small Scale ◽  
Turbulent Shear Stress ◽  
Evolutionary Polynomial Regression ◽  
Boundary Treatment ◽  
Rough Bed

A weakly compressible smoothed particle hydrodynamics (WCSPH) method was developed to model open-channel flow over rough bed. An improved boundary treatment is proposed to quantitatively characterize bed roughness based on the ghost boundary particles (GBPs). In this model, the velocities of GBPs are explicitly calculated by using evolutionary polynomial regression with a multiobjective genetic algorithm. The simulation results show that the proposed boundary treatment can well reflect the influence of wall roughness on the vertical flow structure. A fully developed open channel is established, and its flume length, processing time, and turbulent model are discussed. The mixed-length-based subparticle scale (SPS) turbulence model is adopted to simulate uniform flow in open channel, and this model is compared with the Smagorinsky-based one. For the modified WCSPH model, the results show that the calculated vertical velocity and turbulent shear stress distribution are in good agreement with experimental data and fit better than the calculations obtained from the traditional Smagorinsky-based model.

scholarly journals Measuring the turbulent characteristics in an open channel using the PIV method

2013 ◽  
Vol 14 (3) ◽  
pp. 378-385
Keyword(s):  
Open Channel ◽  
Flow Characteristics ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Mean Velocity ◽  
Vegetation Height ◽  
Hydraulic Behaviour ◽  
Turbulent Characteristics ◽  
Wide Range ◽  
Vegetation Region

Investigation of open channel flows is very important for a wide range of applications, including restoration and enhancement of river aquatic systems. As a result, the scientific community has focused on providing further insights on the flow characteristics in vegetated channels. Vegetation may be submerged or emerged, rigid or flexible with high or low density. For rigid vegetation, the hydraulic behaviour of the channel is similar to the behaviour of a channel with macro-roughness which could be caused by the presence of geometrical elements (e.g. cylinders, cubes). For flexible vegetation, both the flexibility of the vegetation and the hydrodynamic of the flow contribute to the generation of several formations such as erect, gently swaying, and prone. In this study, the characteristics of turbulent flow in an open channel were studied experimentally using Particle Image Velocimetry (PIV). This method assumes that the particles of a fluid faithfully follow the flow dynamics, hence the motion of these seeding particles are used to calculate velocity information of the flow. The experiments were conducted for both impermeable and permeable beds in a channel of 6.5m length, 7.5 cm width and 25 cm height. Two grass-like vegetation types of different height (2 and 6 cm) were used to represent permeable beds. These conditions are typical of flows encountered in sediment transport problems. Hydraulic characteristics such as distributions of velocities, turbulent intensities and Reynolds stress are investigated at a fine resolution using the PIV. Velocity is measured above the vegetation at different heights. Results show that velocity over the vegetation region is a function of the vegetation height and the total flow depth; velocity decreases as the vegetation height increases. In addition, we show that velocities above the vegetation region are much lower than velocities above an impermeable bed. This is due to the turbulent shear stresses and the existence of turbulence in the vegetation region, which reduce the mean velocity above the vegetation region. In addition, results show a region of zero velocity; between 3 and 6 cm and 1 and 2 cm for a 6 cm and 2 cm vegetation. This result shows that 50% of the vegetation behaves like an impermeable bed.

On the definition of the shear velocity in rough bed open channel flows

2006 ◽  
Author(s):  
C Manes ◽  
D Pokrajac ◽  
I McEwan ◽  
J Finnigan ◽  
V Nikora
Keyword(s):  
Open Channel ◽  
Shear Velocity ◽  
Channel Flows ◽  
Open Channel Flows ◽  
Rough Bed ◽  
Definition Of

INFLUENCE OF FLOW RATE AND AXIAL POSITION ON SHEAR STRESSES

2004 ◽  
Vol 04 (01) ◽  
pp. 71-75
Author(s):  
ALI A. SAKHAEIMANESH
Keyword(s):  
Flow Rate ◽  
Artificial Heart ◽  
Heart Valves ◽  
Direct Relationship ◽  
Axial Position ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Close Vicinity ◽  
Velocity Gradients ◽  
Artificial Heart Valves

To locate the maximum and mean turbulent shear stresses in both time and space, and to determine how shear stresses depend on the flow rate and downstream measuring planes of the artificial heart valves, this study was carried out. Maximum and mean turbulent shear stresses estimated at 0.5D downstream of the valves showed a direct relationship with flow rate both in the Jellyfish and St. Vincent valves. The magnitude of both mean and maximum shear stresses in the Jellyfish valve was found to be higher than that of the St. Vincent valve at 0.5 and 1D downstream of the Jellyfish valve. Maximum shear stresses were found in close vicinity to the valve where highly disturbed flow with steep velocity gradients were observed.

Response of open-channel flow to a sudden change from smooth to rough bed

2022 ◽  
Author(s):  
Vijit Rathore ◽  
Nadia Penna ◽  
Subhasish Dey ◽  
Roberto Gaudio
Keyword(s):  
Channel Flow ◽  
Open Channel ◽  
Sudden Change ◽  
Open Channel Flow ◽  
Rough Bed

Estimation of turbulent shear stresses in pulsatile flow immediately downstream of two artificial aortic valves in vitro

1990 ◽  
Vol 23 (12) ◽  
pp. 1231-1238 ◽  
Author(s):  
H Nygaard ◽  
M Giersiepen ◽  
J.M Hasenkam ◽  
D Westphal ◽  
P.K Paulsen ◽  
...  
Keyword(s):  
Pulsatile Flow ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Aortic Valves

scholarly journals Relaxation process modeling in a turbulent boundary layer with nonzero free stream turbulence

1997 ◽  
Vol 3 (3) ◽  
pp. 255-265
Author(s):  
Eugen Dyban ◽  
Ella Fridman
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Process Modeling ◽  
Free Stream ◽  
Equations Of Motion ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Free Stream Turbulence ◽  
Relaxation Effects ◽  
Averaged Equations

In order to analyze the relaxation effects in a turbulent boundary layer with zero and nonzero free stream turbulence, the Reynolds-averaged equations of motion and energy are solved. As the closure of the Reynolds-averaged equations, the transport equation for turbulent shear stresses is used. The proposed approach leads to calculation of the relaxation scales in the turbulent boundary layer with zero and nonzero free stream turbulence. Results for friction coefficients, velocity profiles, shear stresses, thickness of the boundary layer and so called “superlayer” in a flat-plate turbulent boundary layer are presented. The results obtained are in agreement with those available from the experimental data.

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