Sediment Transport In Open Channel Flow Research Articles

A three-phase flow simulation of local scour caused by a submerged wall jet with a water-air interface

Interactions between fluid and hydraulic structures and the resulting bed scouring are complex phenomena that involve three phases: water, air and sediment. This study presents a new rheology-based three-phase flow model that can (i) track the water-air interface in the presence of suspended sediment and (ii) predict the local scour caused by submerged wall jet. A modified volume-of-fluid (VOF) method was used to track the water-air interface, and a modified k-ϵ turbulence model was employed to capture important features of the turbulent flow, including turbulence modulation due to fluid-sediment interaction. The three-phase model was first used to study the sediment transport in open-channel flows in order to evaluate the performance of two models for particle response time, and then employed to simulate the scouring process downstream a submerged wall jet issued from a sluice gate. The simulated bed profiles showed good agreement with the measured. It was demonstrated that the three-phase model could capture important dynamic features such as sediment avalanche.

침수식생 개수로에서 난류 및 부유사 이동 특성

침수식생 개수로 흐름은구조적으로상부영역과식생영역으로구분되는데, 상부영역은 일반 개수로의 흐름특성을 보이며 식생영역은 줄기에 의해 난류가 억제되어 정수식생 조건의 흐름과 유사하게 단순한 흐름특성을 보인다. 본 논문은 침수식생 개수로 흐름의 난류 및 유사이동 특성에 관한 실험연구이다. 이를 위해 폭 0.5m, 길이 12m인 개수로 실험장치를 이용하여수리실험을 실시하였다. 다양한 유량에 대하여 수심비 2～3인 흐름을 구현하였고, 나무원형 실린더를 이용하여 식생을 재현하였다. 평형상태에서 부유사 농도 분포를 측정하기 위해서중앙입경이 75 <TEX>${\mu}M$</TEX>인 모래를 한계조건에 도달하기까지 지속적으로 투입하였다. 유속 성분의 계측을 위하여 레이저 도플러 유속계를 사용하였고, 튜브를 이용한 사이포닝 방식으로 시료를 직접 채취하여 부유사 농도를 측정하였다. 측정된 자료를 이용하여 실험조건에 따른 평균흐름과 난류량의 특성을 살펴보았고, Rouse 수에 따른 부유사 농도 분포를 제시하였다. The open-channel flow with submerged vegetation shows distinct features in two separate regions, namely upper and vegetation layers. In the upper layer, the flow is akin to the open-channel flow, while the flow in the vegetation layer is relatively uniform with suppressed turbulence due to vegetation stems. This paper presents laboratory experiments to investigate the characteristics of turbulent flows and suspended sediment transport in open-channel flows with submerged vegetation. An open-channel facility, 0.5 m wide and 12 m long, was used for laboratory experiments. Various discharges were employed with depth ratios of 2~3, and wooden cylinders were used for vegetation. To make equilibrium suspension, sediment particles of median diameter of 75 <TEX>${\mu}M$</TEX> were fed until capacity condition. Laser Doppler velocimeter was used to measure instantaneous velocity, and direct sampling with vinyl tube was used to measure the concentration of suspended sediment. Using the sampled data, the mean flow and turbulence structures were provided and characteristics of suspended sediment concentration with Rouse number were presented.

Large eddy simulation of sediment transport in open-channel flow

Large Eddy Simulation (LES) is used to investigate the 3D-transport of sediment suspension in an open channel flow at a Reynolds number based on the frictional velocity.An Eulerian model was employed to represent the fluid and the sediment phases. The subgrid-scale fluid stresses were modeled with the Smagorinsky model, whereas subgrid-scale sediment fluxes were based on a gradient approach. To avoid tuning constants, a dynamic procedure was applied. A two-way coupling between sediment and fluid improved the computational description of sediment transport. Sediment concentration profiles and the statistics of sediment fluxes are presented and compared with the Rouse profile and the RANS solution. The results obtained agree well with the theory and with measurements. The LES results also indicate that the assumption of a constant Schmidt number, as is mostly assumed in RANS simulations is erroneous.

RESEARCH PAPERS Large eddy simulation of sediment transport in open-channel flow

RESEARCH PAPERS Large eddy simulation of sediment transport in open-channel flow

Numerical simulations of cellular secondary currents and suspended sediment transport in open-channel flows over smooth-rough bed strips

The flow and transport of suspended sediment in open-channel flows over smooth-rough bed strips were simulated numerically. The flow equations were solved with the aid of the Reynolds stress model. Simulated flow structures are provided and compared with measured data available in the literature. The comparisons indicate that the numerical model successfully predicts the mean flow and turbulence statistics. The sediment distribution of suspended particles in such flows was also simulated. The transport equation for suspended sediment was solved using the eddy diffusivity concept. The computed results show that flows with higher concentration occur over the smooth strips as observed in a river flow during the floods. The eddy diffusivity profile was also obtained and compared with that from an analytical expression reported byWang and Cheng [Advances inWater Resources. 28 (2005) 441–450]

Stochastic Partial Differential Equation-Based Model for Suspended Sediment Transport in Surface Water Flows

A stochastic partial differential equation-based model has been derived based on the law of mass conservation and the Langevin equation of particle displacement to simulate suspended sediment transport in open-channel flows. In this model, the movement of any suspended sediment particle in turbulent flows is modeled as a stochastic diffusion process, which is composed of a drift term and a random term. The stochastic formula of fluid velocity is then substituted into the advection-diffusion (AD) equation to obtain the stochastic partial differential equation (SPDE) for suspended sediment transport. The lattice approximation is applied to solve the SPDE of suspended sediment transport in open channel flow. The proposed model, explicitly expressing the randomness of sediment concentration, has the advantage of capturing any randomly selected scenarios of particle movement and thus a more comprehensive quantitative description of sediment concentrations compared with the deterministic AD equation. As a result, the probability distribution of the sediment transport rate can be characterized based on a number of realizations obtained in the numerical experiments. It is found from the numerical experiments of particle trajectory that the transport of sediment particles is in the form of fully suspended load when the Rouse number is less than one. The ensemble mean sediment concentration of the proposed SPDE, obtained by the Monte Carlo simulation, agrees well with that of the deterministic AD equation.

Influence of Coherent Flow Structures on the Dynamics of Suspended Sediment Transport in Open-Channel Flow

The influence of suspended sediments on coherent flow structures has been studied by simultaneously measuring the longitudinal and vertical components of the instantaneous velocity vector and the instantaneous suspended particle concentration with an acoustic particle flux profiler. The measurements were carried out in clear water and in particle-laden open-channel flows. In both cases, they clearly show the predominance of ejection and sweep phases that are part of a burst cycle. The analysis further demonstrates the importance of the ejection and sweep phases in sediment resuspension and transport. Ejections pick up the sediment at the bed and carry it up through the water column close to the surface. It is shown that ejections and sweeps are in near equality in the near-bottom layer, whereas ejections clearly dominate in the remaining water column. The implications of these results for sediment transport dynamics are discussed.

Sediment-Laden Flow in Open-Channels under Noncapacity and Capacity Conditions

To determine the suspended load component of sediment transport in open-channel flow, the vertical distribution of the concentration of suspended particles is of importance. It is usual to determine this distribution by solving the diffusion-convection equation under appropriate boundary conditions. The exponent in the resulting equation is the Rouse number, defined as z′ = vss/βκ¯u*. The β¯-value has been the subject of much research. In natural alluvial channels the sediment-laden flow is usually in capacity (saturation) condition, implying that the flow will charge (saturate) itself with particles available in the bed load and/or on the bed itself. However, simulation of sediment-laden flow in a laboratory flume is achieved typically by externally adding particles to the flow. Consequently, it is not certain that the flow was in capacity condition. The resulting β¯-values are often values for noncapacity conditions. They should not be used for natural alluvial channels, because they are misleading. Rep...