Numerical study of sediment transport in turbulent two-phase flows around an obstacle

Abstract. Sediment transport is studied as a function of the grain to fluid density ratio using two phase numerical simulations based on a discrete element method (DEM) for particles coupled to a continuum Reynolds averaged description of hydrodynamics. At a density ratio close to unity (typically under water), sediment transport occurs in a thin layer at the surface of the static bed, and is called bed load. Steady, or "saturated" transport is reached when the fluid borne shear stress at the interface between the mobile grains and the static grains is reduced to its threshold value. The number of grains transported per unit surface therefore scales as the excess shear stress. However, the fluid velocity in the transport layer remains almost undisturbed so that the mean grain velocity scales with the shear velocity u*. At large density ratio (typically in air), the vertical velocities are large enough to make the transport layer wide and dilute. Sediment transport is then called saltation. In this case, particles are able to eject others when they collide with the granular bed. The number of grains transported per unit surface is selected by the balance between erosion and deposition and saturation is reached when one grain is statistically replaced by exactly one grain after a collision, which has the consequence that the mean grain velocity remains independent of u*. The influence of the density ratio is systematically studied to reveal the transition between these two transport regimes. Finally, for the subaqueous case, the grain Reynolds number is lowered to investigate the change from turbulent and viscous transport.

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Experimental and numerical study of two-phase flows in arrays of cylinders

Chemical Engineering Science ◽

10.1016/j.ces.2013.08.031 ◽

2013 ◽

Vol 102 ◽

pp. 335-345 ◽

Cited By ~ 29

Author(s):

Pierre Horgue ◽

Frédéric Augier ◽

Paul Duru ◽

Marc Prat ◽

Michel Quintard

Keyword(s):

Numerical Study ◽

Two Phase Flows ◽

Two Phase

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Eulerian and Lagrangian predictions of particulate two-phase flows: a numerical study

Applied Mathematical Modelling ◽

10.1016/0307-904x(84)90062-3 ◽

1984 ◽

Vol 8 (2) ◽

pp. 101-115 ◽

Cited By ~ 184

Author(s):

F. Durst ◽

D. Miloievic ◽

B. Schönung

Keyword(s):

Numerical Study ◽

Two Phase Flows ◽

Two Phase

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Numerical Study of Two-Phase Flow in a Horizontal Pipeline Using an Unconditionally Hyperbolic Two-Fluid Model

Volume 7: Fluids Engineering ◽

10.1115/imece2018-87571 ◽

2018 ◽

Author(s):

Raphael V. N. de Freitas ◽

Carina N. Sondermann ◽

Rodrigo A. C. Patricio ◽

Aline B. Figueiredo ◽

Gustavo C. R. Bodstein ◽

...

Keyword(s):

Volume Fraction ◽

Numerical Study ◽

Fluid Model ◽

Momentum Conservation ◽

Design Stage ◽

Two Phase Flows ◽

Two Phase ◽

Efficient Manner ◽

Two Fluid Model ◽

Two Fluid

Numerical simulation is a very useful tool for the prediction of physical quantities in two-phase flows. One important application is the study of oil-gas flows in pipelines, which is necessary for the proper selection of the equipment connected to the line during the pipeline design stage and also during the pipeline operation stage. The understanding of the phenomena present in this type of flow is more crucial under the occurrence of undesired effects in the duct, such as hydrate formation, fluid leakage, PIG passage, and valve shutdown. An efficient manner to model two-phase flows in long pipelines regarding a compromise between numerical accuracy and cost is the use of a one-dimensional two-fluid model, discretized with an appropriate numerical method. A two-fluid model consists of a system of non-linear partial differential equations that represent the mass, momentum and energy conservation principles, written for each phase. Depending on the two-fluid model employed, the system of equations may lose hyperbolicity and render the initial-boundary-value problem illposed. This paper uses an unconditionally hyperbolic two-fluid model for solving two-phase flows in pipelines in order to guarantee that the solution presents physical consistency. The mathematical model here referred to as the 5E2P (five equations and two pressures) comprises two equations of continuity and two momentum conservation equations, one for each phase, and one equation for the transport of the volume fraction. A priori this model considers two distinct pressures, one for each phase, and correlates them through a pressure relaxation procedure. This paper presents simulation cases for stratified two-phase flows in horizontal pipelines solved with the 5E2P coupled with the flux corrected transport method. The objective is to evaluate the numerical model capacity to adequately describe the velocities, pressures and volume fraction distributions along the duct.

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A Numerical Investigation of Internal and External Two-Phase Flows of a Rotating Disk Atomizer

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2012-72478 ◽

2012 ◽

Author(s):

Cheng-Xian (Charlie) Lin ◽

Long Phan

Keyword(s):

Volume Fraction ◽

Numerical Study ◽

Rotating Disk ◽

Multiphase Model ◽

Two Phase Flows ◽

Two Phase ◽

Liquid Distribution ◽

Liquid Feed ◽

Flow Rate Range ◽

Uniform Liquid

In this paper, a numerical study has been carried out to model and simulate the air-water two-phase flows in and around a rotating disk atomizer, which uses multiple nozzles to breakout the water and forms droplets. The physical problem was simulated with an Eulerian multiphase model. The realizable two-equation turbulence model was used for the turbulent flow. The governing equations were solved with a finite volume based numerical method. The rotary frame approach was used to deal with the spinning disk. Numerical simulation was conducted in a disk rotational speed range of 1000 to 10000 rpm, a liquid feed flow rate range of 100 to 150 gpm. Both uniform and non-uniform liquid distribution conditions were considered. Detailed results about flow velocity and volume fraction fields inside and outside of the atomizer are presented and discussed. It was found that when liquid is nonuniformly distributed through the distributors, some of the nozzles could reach flooding conditions at lower rotational disk speed and liquid feed volume flow rates, as compared to uniform distribution cases.

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