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The floating-vegetation island (FVI) is widely used in river restoration projects for its decontamination effect for the pollutants. A physical experiment is conducted in this paper to study the flow regime near the FVI to better understand the role played by the FVI in the river systems. According to the observed data concerning the mean and turbulent flow characteristics, the flow field can be subdivided into four regions: the incoming flow adjustment region, the initial adjustment region, the shear layer developing region and the fully developed region. The variation of the velocity profile can be described as follows: a "J" shape in the incoming flow adjustment region evolves to an "S" shape in the shear layer developing and fully developed regions. The velocity in the interface between the canopy and the flow in the fully developed region obeys the rule of a mixing layer theory. Based on the experiment data, a three-layer model for estimating the vertical velocity distribution in the fully developed region is established and it performs well as compared with the laboratory findings. [ABSTRACT FROM AUTHOR]

This study focuses on the effects of one-line emergent natural tree (Cupressus Macrocarpa) planted at the edge of the floodplain in a compound open-channel flow. The flow velocity and water level are measured and used to analyze the flow structure. The time averaged and depth-averaged streamwise velocity distributions with root mean square (rms) and time series of streamwise velocity distrbution are analyzed. The velocity distribution considerably changes along the compound channel. The streamwise velocity distribution fits with logarithmic distribution in the non-vegetated case, but for vegetated cases, the streamwise velocity distribution shows S shaped profile at the 1/3 part of floodplain (Bf / 3) and main channel (Bm / 3) close to the boundary between floodplain and main channel. Additionally, it is obtained that the presence of tree line increases turbulence intensity over the compound open-channel. Moreover, an oscillation period is obtained in the flow caused by tree line by analyzing time series of the streamwise velocity distribution. The oscillation is present everywhere in the floodplain and present at almost Bm / 3 part of the main channel which is close to the junction between floodplain and main channel. [ABSTRACT FROM AUTHOR]

A pneumatic annular flume is designed to simulate the current induced by the wind acting on the water surface in shallow lakes and the experiments are conducted to investigate the influence of submerged and emergent flexible vegetations of different densities on the flow characteristics (e.g., the flow velocity, the turbulence intensity, the vegetal drag coefficient and the equivalent roughness coefficient) at different wind speeds. Vallisneria natans ( V. natans ) and Acorus calamus ( A. calamus ) widely distributed in Taihu Lake are selected in this study. It is indicated that the vertical distribution profiles are in logarithmic-curves. The stream-wise velocity rapidly decreases with the increasing vegetation density. The flow at the lower layer of the vegetation sees compensation current characteristics when the vegetation density is the largest. The turbulence intensity in the flume without vegetation is the highest at the free surface and it is near the canopy top for the flume with V. natans . The turbulence intensity near the bottom in the flume with vegetation is smaller than that in the flume without vegetation. A. calamus exerts much larger resistance to the flow than V. natans . The variations of and caused by the vegetation density and the wind speed are also discussed. [ABSTRACT FROM AUTHOR]

The velocity profile around cells in a flow chamber coated with the immobilized protein and the endothelial cells is studied using the micro particle image velocimetry (PIV). The main purpose is to study the effect of the endothelial cells on the local hydrodynamic environment and the local shear rates above a single polymorphonuclear neutrophil (PMN) and a melanoma cell when they adhere to different immobilized protein substrates. Micro-PIV images are taken in the top-view and the side-view under 10 X and 40 X objective lens and the ensemble correlation method is used to analyze the data. The results show that the endothelial monolayer has changed the patterns of the flow velocity profile of the side-view flow on the chamber bottom, and also increased the wall shear rates. The melanoma cells adhered on the immobilized fibrin disturb the local flow more than those adhered on the immobilized fibrinogen, but one sees no significant difference between the local shear rates above the PMNs adhered on the immobilized fibrinogen and those above the PMNs adhered on the immobilized fibrin. [ABSTRACT FROM AUTHOR]

In this paper, we attempt to quantify the mean and turbulent flow fields around live macroalgae within a tidal inlet in Norway. Two Laminaria digitata specimens ∼0.50m apart were selected for detailed study and a profiling ADV was used to collect 45 velocity profiles, each composed of up to seven 0.035 m-high profiles collected for 240 s at 100 Hz, at a streamwise spacing of 0.25 m and cross-stream spacing of 0.20 m. To quantify the impact of the macroalgae, measurements were repeated over a sparser grid after the region had been completely cleared of algae and major roughness elements. [ABSTRACT FROM AUTHOR]

Recently, many channelized rivers tend to be heavily vegetated due to regime shifts in hydrological, fluvial and ecological processes. Dense vegetation in a river frequently obstructs a flood flow and reduces conveyance capacity of channels. On the other hand, river vegetation provides various ecological services such as habitats for various species and life, natural cycle of organic and inorganic substances, etc‥ It is of engineering importance to understand vegetation hydrodynamics in order to preserve vegetation nature and keep a certain level of flow conveyance capacity. In view that willows tend to be densely vegetated along the shoreline of floodplains or sandbars, a field measurement, a physical model experiment and a numerical analysis were carried out for investigating hydrodynamics in an open channel with riparian vegetation. Discussion was made focusing on flow and shear layer structures developed around the vegetation canopy. [ABSTRACT FROM AUTHOR]

The radial wall jet is a flow configuration that combines the radial jet and the wall jet. This article presents a simulation of the radial wall jet by applying the transition Shear-Stress Transport (SST) model. Tanaka’s experimental data are used for validation. The computed velocity profiles agree well with the experimental ones. The distributions of the velocity on cross-sections show a similarity in the main region and the profiles are different with those of the free radial jet or the wall jet, because the presence of the wall limits the expansion of the jet. By introducing the equivalent nozzle width, the maximum velocity decays and the half-width distributions are normalized, respectively. In addition to compare the flow field with experiments, this paper also analyzes the dilution effect of radial wall jets in terms of the concentration distributions. The concentrations on the wall keep constant within a certain distance from the nozzle. And the concentration distributions also show a similarity in the main region. Both the decays of the maximum concentration and the distributions of the concentration half-width fall into a single curve, respectively. The dilution effect of radial wall jets is thus verified. [ABSTRACT FROM AUTHOR]

This article applies the realizable k-ε model to simulate the buoyant wall jet and gives the results of cling length, centerline trajectory and temperature dilutions at certain sections. The comparison between the numerical results and Sharp’s experimental data indicates that the model is effective in estimating velocity distribution and temperature dilutions. The velocity profiles at the cental plane and z-plane both show a strong similarity at certain distance from the nozzle, and the distributions of velocity and temperature dilutions also exhibit a similarity along the axial direction at centerline in the near-field. Based on the results, the article gives the corresponding relationships between the distance and the dilutions of velocity and temperature, which is useful in predicting the behavior of the wall buoyant jet. [ABSTRACT FROM AUTHOR]

Aquatic vegetation can influence the transport of sediment and contaminants by changing the mean velocity and turbulent flow structure in channels. It is important to understand the hydraulics of the flows over vegetation in order to manage fluvial processes. Experiments in an open-channel flume with natural vegetation were carried out to study the influence of vegetation on the flows. In a half channel with two different densities of vegetation, the flow velocity, Reynolds stresses, and turbulence intensities were measured using an Acoustic Doppler Velocimeter (ADV). We obtained velocity profiles in the lateral direction, Reynolds stresses in the vertical direction, and the flow transition between the vegetated and non-vegetated zones in different flow regimes. The results show that the streamwise velocity in the vegetated zone with higher density is almost entirely blocked. Reynolds stress distribution distinguishes with two different regions: inside and above the vegetation canopies. The turbulence intensities increase with increasing Reynolds number. The coherent vortices dominate the vertical transport of momentum and are advected clockwise between the vegetated zone and non-vegetated zone by secondary currents (a relatively minor flow superimposed on the primary flow, with significantly different speed and direction), generated by the anisotropy of the turbulence. [ABSTRACT FROM AUTHOR]