Modeling depth-averaged streamwise velocity in straight trapezoidal compound channels with ice cover

Liu

et al. 2021

Environ Sci Pollut Res

Self Cite

Floating vegetation islands (FVIs) have been widely utilized in various river ecological restoration projects due to their ability to purify pollutants. FVIs float at the surface of shallow pools with their roots unanchored in the sediment. Biofilm formed by roots under islands filters nutrients and particles in the water flowing through it. Flow field disturbance will occur and transverse distribution of flow velocity will change due to the existence of FVIs. Transport efficiency of suspended solids, nutrients, and pollutants will also be altered. A modified analytical model that considers effects of boundary friction, drag force of vegetation, transverse shear turbulence, and secondary flow is established to predict transverse variation of depth-averaged streamwise velocity for the open-channel flow with FVIs using Shiono and Knight method. The simulation results with suitable boundary conditions successfully predicted lateral profile of the depth-averaged streamwise velocity compared with the experimental results of symmetrical and unsymmetrical arrangements of FVIs. Hence, the presented model can provide guidance for investigating flow characteristics of rivers with FVIs.

Section: Introductionmentioning

confidence: 99%

Transverse distribution of the streamwise velocity for the open-channel flow with floating vegetated islands

Liu

et al. 2021

Environ Sci Pollut Res

Self Cite

“…where α is a constant, D(y) is the local flow depth and used as the length scale, f c U is the friction velocity and used as the velocity scale, and c f is the comprehensive friction coefficient. For the ice-covered compound channels, both the ice cover resistance and the channel bed friction contribute to the comprehensive friction coefficient c f , which can be derived as (Wang et al, 2020):…”

Section: Modeling Of the Transverse Momentum Exchangementioning

confidence: 99%

“…The eddy viscosity

{ν_{t}}^{'}

from the turbulence generated by the ice cover and the channel bed bottom can be defined on the basis of the Elder formulation:

{ν_{t}}^{'} = α D (y) \sqrt{c_{f}} U (y)

where α is a constant, D ( y ) is the local flow depth and used as the length scale,

\sqrt{c_{f}} U

is the friction velocity and used as the velocity scale, and c f is the comprehensive friction coefficient. For the ice‐covered compound channels, both the ice cover resistance and the channel bed friction contribute to the comprehensive friction coefficient c f , which can be derived as (Wang et al., 2020):

c_{f} = \frac{g}{χ_{b} + χ_{i}} {[\frac{{n_{b}}^{3 / 2} + ζ {n_{i}}^{3 / 2}}{(1 + ζ) R_{d}}]}^{1 / 3} (χ_{b} n_{b}^{3 / 2} + χ_{i} {n_{i}}^{3 / 2})

where

χ_{b}

is the dimensionless wetted perimeter of the channel bed per unit width;

χ_{i}

is the dimensionless wetted perimeter of the ice cover per unit width; ζ is the ratio of

χ_{i}

χ_{b}

; R d is the comprehensive hydraulic radius, and

R_{d} = A / (χ_{b} + χ_{i})

.…”

Section: Modeling Of the Transverse Momentum Exchangementioning

confidence: 99%

Turbulence Structure and Momentum Exchange in Compound Channel Flows With Shore Ice Covered on the Floodplains

Water Resources Research

Huai

Guo

et al. 2021

Self Cite

Seasonal ice cover is frequently encountered in rivers located in cold regions that expose to freezing temperatures (Kirillin et al., 2012;Wazney et al., 2019), such as the Nelson River in Canada (Peters et al., 2017), the Mississippi River in America (Ettema, 2002), and the Kanas Lake in China (see Figure 1). Ice cover can have a significant impact on society and the economy. For example, the thawing of the ice cover during the spring season may result in a downstream flood, while the floating ice poses threats to hydroelectric equipment, navigation, and municipal drinking water intakes (Morse & Hicks, 2005;Zare et al., 2016). Due to its practical importance, river ice cover has attracted considerable interest from researchers in the past several decades. Teal et al. (1994) applied point-measurement methods to estimate the vertical profiles of streamwise velocity for the ice-covered channels. Muste et al. (2000) carried out laboratory experiments to determine the effect of the ice cover on the flow fields, turbulence characteristics, and sediment transport rates. Robert and Tran (2012) conducted the laboratory experiment to show that the additional ice sheet and its roughness strongly affected the vertical profiles of the Reynolds shear stresses and the turbulent kinetic energy. Ren et al. (2020) used linearized velocity potential and thin-plate elastic theory to investigate the hydroelastic waves in an ice-covered channel. Other studies of the ice-covered channel flows focused on obtaining the exact solution to the eddy viscosity (Guo et al., 2017); investigating the nonlinear interaction between a floating ice sheet and a water wave (Xia & Shen, 2002); and developing the analytical model of the transverse depth-averaged streamwise velocity distribution (Zhong et al., 2019).The turbulence generated underneath the ice cover will inevitably interact with that generated by the roughness of the channel bed (

“…The ice sheet in some Canadian rivers is at least 0.6 m thick and lasts for at least 4 months [1]. The wetted perimeter of the cross section and flow resistance in ice-covered flows increases with the presence of the ice sheet, which significantly affects the hydraulic characteristics of river and topographical features and greatly change the flow velocity distribution, flow transport capacity and sediment transport rate [2][3][4][5][6][7][8][9][10][11]. Therefore, it is necessary to study the ice-covered flows.…”

Section: Introductionmentioning

confidence: 99%

Analytical Models of Velocity, Reynolds Stress and Turbulence Intensity in Ice-Covered Channels

Zhang

et al. 2021

Water

Ice cover in an open channel can influence the flow structure, such as the flow velocity, Reynolds stress and turbulence intensity. This study analyzes the vertical distributions of velocity, Reynolds stress and turbulence intensity in fully and partially ice-covered channels by theoretical methods and laboratory experiments. According to the experimental data, the vertical profile of longitudinal velocities follows an approximately symmetry form. Different from the open channel flow, the maximum value of longitudinal velocity occurs near the middle of the water depth, which is close to the channel bed with a smoother boundary roughness compared to the ice cover. The measured Reynolds stress has a linear distribution along the vertical axis, and the vertical distribution of measured turbulence intensity follows an exponential law. Theoretically, a two-power-law function is presented to obtain the analytical formula of the longitudinal velocity. In addition, the vertical profile of Reynolds stress is obtained by the simplified momentum equation and the vertical profile of turbulence intensity is investigated by an improved exponential model. The predicted data from the analytical models agree well with the experimental ones, thereby confirming that the analytical models are feasible to predict the vertical distribution of velocity, Reynolds stress and turbulence intensity in ice-covered channels. The proposed models can offer an important theoretical reference for future study about the sediment transport and contaminant dispersion in ice-covered channels.