The Experts below are selected from a list of 19479 Experts worldwide ranked by ideXlab platform
G Q Chen - One of the best experts on this subject based on the ideXlab platform.
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solute dispersion in Open Channel Flow with bed absorption
Journal of Hydrology, 2016Co-Authors: Ping Wang, G Q ChenAbstract:Abstract Reactive solute dispersion is of essential significance in various ecological and environmental applications. It is only qualitatively known that boundary absorption depletes pollutant around the boundary and reduces the concentration nearby. All the existing studies on this topic have been focused on the longitudinally distributed mean concentration, far from enough to fully characterize the transport process with tremendous cross-sectional concentration nonuniformity. This work presents an analytical study of the evolution of two-dimensional concentration distribution for solute dispersion in a laminar Open Channel Flow with bed absorption. The fourth order Aris-Gill expansion proposed in our previous study (Wang and Chen, 2016b) is further extended for the case with bed absorption to cover the transitional effects of skewness and kurtosis. Results reveal the extremely nonuniform cross-sectional concentration distribution, and demonstrate that concentration at the bed instead of the mean should be used for reliable quantification of the absorption flux. The accurate two-dimensional concentration distribution presented in this study brings important environmental implications such as risk assessment associated with peak concentration position and duration of toxic pollutant cloud in Open Channel waters.
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analytical solution for scalar transport in Open Channel Flow slow decaying transient effect
Journal of Hydrology, 2014Co-Authors: G Q ChenAbstract:Summary It is well known that the extensively applied Taylor dispersion model only predicts the longitudinally distributed mean concentration. While at the same time, applications as the risk assessment for toxic pollutant transport in environmental fluid Flows require detailed information on the cross-sectional concentration distribution. As shown by some recent progress (Wu, Z., Chen, G.Q., 2014, J. Fluid Mech., 740, 196–213.), the deviation of transverse concentration from the mean can be remarkable for a very long time, which is termed as the slow-decaying transient effect. Thus it is important to examine the process of concentration evolution for scalar transport in laminar Open Channel Flow. In this paper, the idealized case of a uniform and instantaneous scalar release across the Channel is analytically explored by a two-scale perturbation analysis. The validity of the Taylor dispersion model for the mean concentration is discussed by the obtained analytical solution. For the first time, the two-dimensional concentration distribution for the Open Channel Flow is explored analytically. Corresponding time scales for the concentration evolution are determined, indicating that the process for the vertical concentration difference to diminish will be much slower than that for the mean concentration to become Gaussian. Dominated by the so-called slow-decaying transient effect, the uniform vertical distribution needs to be modified to predict the vertical concentration distribution correctly.
Zhonghua Yang - One of the best experts on this subject based on the ideXlab platform.
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three layer model for vertical velocity distribution in Open Channel Flow with submerged rigid vegetation
Advances in Water Resources, 2009Co-Authors: Wenxin Huai, Yuhong Zeng, Z G Xu, Zhonghua YangAbstract:Abstract Based on the detailed laboratory experiments and theoretical analysis, a new three-layer model is proposed to predict the vertical velocity distribution in an Open Channel Flow with submerged vegetation. The time averaged velocity and turbulence behaviour of a steady uniform Flow with fully submerged artificial rigid vegetation was measured using a 3D Micro ADV, and the vertical distribution of velocity and Reynolds shear stress at different vegetation height, vegetation density and measuring positions were obtained. The results show that the velocity profile consists of three hydrodynamic regimes (i.e. the upper non-vegetated layer, the outer and bottom layer within vegetation); accordingly different methods had been adopted to describe the vertical velocity distribution. For the upper non-vegetated layer, a modified mixing length theory combined with the concept of ‘the new vegetation boundary layer’ was adopted, and an analytical model was presented to predict the vertical velocity distribution in this region. For the bottom layer within vegetation, the depth average velocity was obtained by numerically solving the momentum equations. For the upper layer within vegetation, the analytical solution was presented by expressing the shear stress as a formula fitted to the experimental data. Finally, the analytical predictions of the vertical velocity over the whole Flow depth were compared with the results obtained by other researchers, and the good agreement proved that the three-layer model can be used to predict the velocity distribution of the Open Channel Flow with submerged rigid vegetation.
Wenxin Huai - One of the best experts on this subject based on the ideXlab platform.
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prediction of velocity distribution in straight Open Channel Flow with partial vegetation by singular perturbation method
Applied Mathematics and Mechanics-english Edition, 2016Co-Authors: Suwen Song, Yuhong Zeng, Wenxin HuaiAbstract:A numerical analysis model based on two-dimensional shallow water differential equations is presented for straight Open-Channel Flow with partial vegetation across the Channel. Both the drag force acting on vegetation and the momentum exchange between the vegetation and non-vegetation zones are considered. The depth-averaged streamwise velocity is solved by the singular perturbation method, while the Reynolds stress is calculated based on the results of the streamwise velocity. Comparisons with the experimental data indicate that the accuracy of prediction is significantly improved by introducing a term for the secondary current in the model. A sensitivity analysis shows that a sound choice of the secondary current intensity coefficient is important for an accurate prediction of the depth-averaged streamwise velocity near the vegetation and non-vegetation interfaces, and the drag force coefficient is crucial for predictions in the vegetation zone.
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three layer model for vertical velocity distribution in Open Channel Flow with submerged rigid vegetation
Advances in Water Resources, 2009Co-Authors: Wenxin Huai, Yuhong Zeng, Z G Xu, Zhonghua YangAbstract:Abstract Based on the detailed laboratory experiments and theoretical analysis, a new three-layer model is proposed to predict the vertical velocity distribution in an Open Channel Flow with submerged vegetation. The time averaged velocity and turbulence behaviour of a steady uniform Flow with fully submerged artificial rigid vegetation was measured using a 3D Micro ADV, and the vertical distribution of velocity and Reynolds shear stress at different vegetation height, vegetation density and measuring positions were obtained. The results show that the velocity profile consists of three hydrodynamic regimes (i.e. the upper non-vegetated layer, the outer and bottom layer within vegetation); accordingly different methods had been adopted to describe the vertical velocity distribution. For the upper non-vegetated layer, a modified mixing length theory combined with the concept of ‘the new vegetation boundary layer’ was adopted, and an analytical model was presented to predict the vertical velocity distribution in this region. For the bottom layer within vegetation, the depth average velocity was obtained by numerically solving the momentum equations. For the upper layer within vegetation, the analytical solution was presented by expressing the shear stress as a formula fitted to the experimental data. Finally, the analytical predictions of the vertical velocity over the whole Flow depth were compared with the results obtained by other researchers, and the good agreement proved that the three-layer model can be used to predict the velocity distribution of the Open Channel Flow with submerged rigid vegetation.
Gareth Pender - One of the best experts on this subject based on the ideXlab platform.
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macroturbulent structure of Open Channel Flow over gravel beds
Water Resources Research, 2001Co-Authors: A B Shvidchenko, Gareth PenderAbstract:The turbulent structure of Open-Channel Flow over a mobile gravel bed was investigated in an 8 m long, 0.3 m wide, and 0.3 m deep tilting flume. A Flow visualization technique was used and complemented by measurements of Flow velocity fluctuations near the bed. The experiments reveal that turbulent Flow consists of a sequence of large-scale eddies with a vertical size close to the Flow depth, an average length equal to four to five depths, and a width of about two depths. The downstream motion of these eddies causes quasiperiodic fluctuations of the local Flow velocity components. The development of longitudinal troughs and ridges on the mobile bed and preferential transport of bed particles along troughs are related to the effect of the eddies. The experimental results indicate that the depth-scale eddies are an important turbulence mechanism contributing to sediment transport.
Yee-meng Chiew - One of the best experts on this subject based on the ideXlab platform.
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review of seepage effects on turbulent Open Channel Flow and sediment entrainment
Journal of Hydraulic Research, 2008Co-Authors: Yee-meng Chiew, Nian-sheng ChengAbstract:This paper presents a review on the state-of-the-art knowledge of how seepage affects the turbulence characteristics in Open-Channel Flow and its implication on sediment entrainment. Published literature shows that some effects have been intensively examined and the results are well known, such as seepage effects on mean Flow velocity distributions. Understanding of the other effects remains rudimentary, such as variations of turbulence intensity and bed shear stresses. In fact, many of these issues remain ambiguous with contradicting inferences and conclusions. For example, the published literature is still not unanimous as to how turbulence intensities, bed shear stresses and bed particle stability change in the presence of seepage. By reviewing literature in this area published over the past 35 years, this paper highlights the main conflicting results and attempts to explain these deviations with certain recommendations.
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velocity distribution of turbulent Open Channel Flow with bed suction
Journal of Hydraulic Engineering, 2004Co-Authors: Xingwei Chen, Yee-meng ChiewAbstract:This study investigates theoretically and experimentally the velocity distributions of turbulent Open Channel Flow with bed suction. A velocity profile with a slip velocity at the bed surface and an origin displacement under the bed surface is proposed and discussed. Based on this assumption, a modified logarithmic law is derived. The measured experimental velocity distribution verifies the accuracy of the theoretically derived profile. The data show a significant increase in the near bed velocity and a velocity reduction near the water surface, resulting in the formation of a more uniform velocity distribution. The values of the origin displacement, slip velocity and shear velocity are found to increase with increasing relative suction. The measured data show the occurrence of two Flow regions in the suction zone: a transitional region in which the velocity readjusts rapidly; and an "equilibrium" region.
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Turbulent Open-Channel Flow with upward seepage
Journal of Hydraulic Research, 1998Co-Authors: Nian-sheng Cheng, Yee-meng ChiewAbstract:Measurements of turbulent Open-Channel Flow subjected to an upward bed seepage were performed in a laboratory flume using a two-dimensional Acoustic Doppler Velocimeter and a minipropeller. The experimental results show that the boundary seepage affects the time-mean streamwise velocity, the rnis values of the velocity fluctuations, the Reynolds shear stress and the bed shear stress in Open-Channel Flow. Along the seepage zone, the mean streamwise velocity increases much more in the surface layer than that in the near-bed region, whereas the turbulent intensities and Reynolds shear stress increase significantly in the near-bed region. The bed shear stress that was computed using the momentum integral equation shows a steady reduction with increasing upward seepage velocity.
