Study Of Mechanism Of Solid-Liquid Two-phase Flow And Two-phase Flow Model Applied In Engineering

Solid-liquid two-phase flow are widely encountered in hydraulic engineering, environmental engineering, energy engineering, chemical industry and so on, such as sediment transport in hydraulic engineering, particle separation and dynamics of suspensions in the chemical industry, erosion processes in coastal and river engineering and wastewater discharge in environmental engineering. The investigations on sediment in river&costal area and wastewater discharge in environmental engineering are helpful for understanding the mechanism of sediment motions and the diffusion and transport law of wastewater, accurately predicting the tendency of bed deformation and the distribution of wastewater, and thus address the various issues encountered in hydraulic engineering and environmental engineering projects.Through combination of model experiment, numerical simulation and theoretical analysis, the typical solid-liquid two-phase flows, such as water scouring sediment-bed, sediment-laden turbulent jets and wastewater discharging, are deeply studied in this paper. The main contents are as follows:1-. The Eulerian two-phase model and the Mixture two-phase model are introduced in detail in this paper. The Eulerian two-phase model assumes that the sediment-laden flow consists of sediment and water phases, which are separate, yet form interpenetrating continua, the laws for the conservation of mass and momentum are satisfied for each phase individually and coupling is achieved through pressure and interphasal exchange coefficients. The mixture model is a simplified multiphase model that can be used in different ways. It can be used to model multiphase flows where the phases move at different velocities, but assume local equilibrium over short spatial length scales. The mixture model can model n phases (fluid or particulate) by solving the momentum, continuity, and energy equations for the mixture, the volume fraction equations for the secondary phases, and algebraic expressions for the relative velocities. A modified standard k-s turbulent model is used to close Mixture model.2?A2D submerged impinging vertical jet scour was conducted to study the influence of water depth and jet initial velocity on scour profile. And experimental data reveal that the scour profiles are self-similar. Expressions for the maximum scour depth under static scour equilibrium and dynamic scour equilibrium are obtained by using dimension analysis and regression analysis, and other expressions for scour characteristic length are also obtained.3?Sediment erosion by submerged jets and scouring funnel in front of bottom orifice are simulated using Eulerian two-phase model.The erosion of loose beds by submerged circular impinging vertical turbulent jets and2D submerged impinging vertical jet scour wee simulated, the predictions of eroded bed profiles agree well with laboratory measurements and self-designed experiments. Analysis of the simulated results reveals that:the velocity field of the jet water is different with various scouring intensities; the scour depth and shape are mainly influenced by the driving force of the water when the density, diameter and porosity of the sand are considered; and the porosity is an important contributor to sediment erosion. In this study, the scour depth, the height of dune and the velocity of the pore water increase with increasing porosity.Erosion of loose beds acted by submerged plane turbulent jets was simulated, computational results compared well with the experimental ones. The differences between dynamic scour results and static scour results were reasonably explained; A ensuing calculations was needed to solve the inadequacy of the parameterization of particle-turbulence interaction terms and the time delay of flow adjustment following the scour.The scouring funnel in front of a bottom orifice under fixed water levels was simulated. Considering flow-particle and particle-particle interactions, predictions of scouring funnel shape agreed well with laboratory measurements. Results reveal that: the non-dimensional maximum scour hole parameters, depth dm/do, length lm/do, and half-width wm/do, are linear with densimetric Froude number Fo, the main parameter describing the scour hole; centerline scour depth Dc and half-scour width Wr vary according to a power law, and the transverse scour profiles exhibit strong similarities; the velocity distribution of water is confined within the sink-like area near the orifice, and the mutual impact of flows at azimuthal sections and resistances of walls and sand layer produce a vortex in the scour hole, that causes sand particles to be suspended in the water; the exchanging water in pore water is the main contributor in forcing sand to move, and transporting the sand in the same direction as the pore water along azimuthal sections.4?Slurry jets in a static uniform environment were simulated with a two-phase Mixture model. The computational results were in agreement with previous laboratory measurements. The characteristics of the two-phase flow field and the influences of hydraulic and geometric parameters on the distribution of the slurry jets were analyzed on the basis of the computational results. The calculated results reveal that if the initial velocity of the slurry jet is high, the jet spreads less in the radial direction. When the slurry jet is less influenced by the ambient fluid (when the Stokes number St is relatively large), the turbulent kinetic energy k and turbulent dissipation rate ?, which are relatively concentrated around the jet axis, decrease more rapidly after the slurry jet passes through the nozzle. For different values of St, the radial distributions of streamwise velocity and particle volume fraction are both self-similar and fit a Gaussian profile after the slurry jet fully develops. The decay rate of the particle velocity is lower than that of water velocity along the jet axis, and the axial distributions of the centerline particle streamwise velocity are self-similar along the jet axis. The pattern of particle dispersion depends on the Stokes number St. When St=0.39, the particle dispersion along the radial direction is considerable, and the relative velocity is very low due to the low dynamic response time. When St=3.08, the dispersion of particles along the radial direction is very little, and most of the particles have high relative velocities along the streamwise direction.5?Sediment-laden jets were simulated with an Eulerian two-phase model that implements Euler-Euler coupled governing equations for fluid and solid phases. The computational results compared well with previous laboratory measurements. The calculation results reveal that if the initial velocity of the sediment-laden jet is high, the jet is sprayed higher and spreads further in the radial direction. The turbulent kinetic energy k and turbulent dissipation rate ?, whose decay rates are higher than that of the jet velocity, decrease rapidly after the sediment-laden jet enters the nozzle. For different values of the exit densimetric Froude number Fo, the profiles of deposited sediment and the axial distributions of the jet velocity, density deficit and turbulent kinetic energy are self-similar on a certain jet axis. The decay rate of the sand velocity is higher than that of water velocity along the axis of the sediment-laden jet, and if the sediment particle has a higher settling velocity, it has higher inertia and spreads less radially.6?Marine wastewater discharges from multiport diffusers were investigated by numerically solving three-dimensional and uncompressible two-phase flow fields. A mixture model simulated this flow which was closed by a modified standard k-? model. Computations were performed for two values of the port spacings s/H with different current Froude numbers F. Computational results compared well with previous laboratory measurements. Numerical results reveal that for both the closely spaced (s/H=0.21) and widely spaced (s/H=3.0) ports, the normalized dilution Sn becomes independent of F; further, the length of the near field xn and the spreading layer thickness hn are functions of F. For the closely spaced ports, the wastewater discharge behaves like a line plume, the Coanda effect is obvious, quasi-bifurcation is present, horseshoe structures of the jets in the planes are rapidly produced and then squashed and elongated, and the jet trajectories based on maximum velocity precede those based on maximum concentration. For the widely spaced ports, the wastewater discharge behaves like a point plume, the Coanda effect is not obvious, bifurcation is present, horseshoe structures of the jets in the planes are gradually produced and become ellipses, and the jet trajectories based on maximum velocity are similar to those based on maximum concentration.