Modeling Multiphase Flows
Simcenter STAR-CCM+ supports several types of multiphase models, each with their own workflow. Use this section to help identify the choice of models that are appropriate for the type of multiphase analysis that you intend to simulate.
The 多相流体 section gives you an overview of each of the available multiphase models and their general applications. Some of these models can also be used in different combinations to suit different types of multiphase processes.
To model multiphase flow:- Prepare the required geometry, regions, interfaces, as appropriate to your simulation.
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Generate a quality mesh to represent the multiphase volume.
You are advised to refine the mesh by increasing the resolution in significant areas or volumes of the geometry.
For example:- Refine the mesh on and around the free surface.
- Refine the mesh on and around jets.
- Create a higher resolution mesh in narrow volumes.
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Depending on the multiphase flow regimes that you want to model, and the other
requirements of your simulation, decide on the multiphase model that is the most
suitable and follow the steps in the individual workflows:
Applicable Flow Regime Multiphase Model Dispersed flows of droplets, bubbles, and solid particles with low volume fraction of the dispersed phase. - Dispersed Multiphase (DMP)
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If you are interested in only the phases that are dispersed, and interactions with the background fluid is not the main objective, use the Dispersed Multiphase (DMP) model. This lightweight model solves for the dispersed phases superimposed on the solution. Where possible it can be used to avoid the large number of parcels that is required with the LMP model. One-way coupling where only the continuous phase influences the dispersed phase is the default setting in Simcenter STAR-CCM+. Optionally, you can activate two-way coupling to take into account the effects of the dispersed phase on the continuous phase.
An example of this type of flow is airfoil icing applications where the background air affects the water droplets in the wing, however, the water droplets do not have any impact on the air.
Dispersed flows of bubbles, droplets, and solid particles. - Eulerian Multiphase (EMP)
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If the phases are expected to be mixed on length scales smaller than the length scales to resolve, and coexist everywhere in the flow domain, use the Eulerian Multiphase (EMP) with the Continuous-Dispersed Topology phase interaction model.
In the Eulerian Multiphase (EMP) model, each distinct phase has its own set of conservation equations. It is assumed that you are interested in the time-averaged behavior of the flow, rather than the instantaneous behavior. With the EMP model with Continuous-Dispersed Topology, phase change at the interface and near wall, crystal growth, emulsion, suspension, particle size distribution can also be captured.
Coexisting and interchanging dispersed and stratified flows - Eulerian Multiphase (EMP)
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In simulations where there is a possibility of locally dispersed and stratified flows within the same domain, Eulerian Multiphase (EMP) with the Multiple Flow Regime Topology phase interaction model
The Multiple Flow Regime phase interaction model relies on adaptively using appropriate closure based on local regime. It also relies on additional modeling for large scale interface such as turbulence damping, surface-tension, and entrainment modeling.
Stratified thin liquid film flows over surfaces. - Fluid Film
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If the phase is expected to be a thin film on solid boundaries, where complex interactions can occur between the film and the surrounding environment use the Fluid Film model. This model is suitable for fluid impingement, wave stripping, gravity driven flow, and shear flow.
Modeling a fluid film on surface requires the definition of a continuous background fluid. You define this background fluid in the physics continuum using a single or multiphase flow model with the associated fluid materials. Simcenter STAR-CCM+ uses a shell region as the space within which the fluid film flows.
Dispersed flows of mixtures of bubbles in liquid or droplets in gas.
- Mixture Multiphase (MMP)
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If the mixture of phases can be modeled by a single set of weighted physical properties, use the Mixture Multiphase (MMP) model.
The Mixture Multiphase (MMP) model treats mass, momentum, and energy as mixture quantities rather than phase quantities. Simcenter STAR-CCM+ solves transport equations for the mixture as a whole, and not for each phase separately. Phase change can also be modeled. This model is computationally more efficient than models that simulate each phase separately.
Dispersed flows of two thermodynamic phases of the same material. - Two-Phase Thermodynamic Equilibrium
- If the mixture of phases is two phases of the same substance, for example, water and steam which are in thermal equilibrium, use the Two-Phase Thermodynamic Equilibrium model. The model assumes a homogeneous single-phase system for the mixtures, resulting in computationally more efficient simulations.
Stratified flows (free surfaces). - Volume of Fluid (VOF)
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If each phase constitutes a large structure, with a relatively small total contact area between phases, use the Volume of Fluid (VOF) model. This model is used to solve problems involving immiscible fluid mixtures, free surfaces, and phase contact time. In such simulations, there is no need for extra modeling of inter-phase interaction, and the model assumption that all phases share velocity, pressure, and temperature fields becomes a discretization error.
A good example of this type of flow is sloshing flow in a water tank, where the free surface always remains smooth.
Dispersed flows of solid particles. - Discrete Element Method (DEM)
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If you are interested in modeling phases that constitute typically solid/granular materials of many interacting discrete objects, where particle shape and collision behavior is important, use the Discrete Element Method (DEM) model. This model is an extension of the LMP methodology, used to model the behavior of large numbers of densely packed particles of different sizes and shapes. DEM can be applied to regions with or without a volume mesh.
See Modeling Discrete Element Method Flow and Modeling Meshfree Discrete Element Method Flow.
Dispersed flows of discrete particles (bubbles, droplets, solid particles) with low volume fraction of the particles. - Lagrangian Multiphase (LMP)
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If interactions of particles with the continuous phase, rather than with each other, dominate their motion, and the dispersed phases are dilute use the Lagrangian Multiphase (LMP) model. This model is suited for cases where the volume fraction of the dispersed phase is relatively small, and interaction with solid boundaries is important. The equations of motion are solved for representative parcels, and each parcel represents many physical droplets or particles. One-way or two-way coupling with the background fluid (physics continuum) is optional in a LMP simulation.
SCR or spray coating are good examples of where the LMP model can be used.
Fast and dynamic free surface flows where you analyze the liquid phase behavior and the gas phase can be neglected. - Smoothed-Particle Hydrodynamics (SPH)
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If you are interested in simulating highly dynamic free-surface flows with adaptability to changing geometries use the Smoothed-Particle Hydrodynamics (SPH) model. The meshless approach of SPH enables dynamic adaptation of its particle distribution without the constraints imposed by a fixed mesh.
The SPH model uses phase models to define the fluid (liquid) particles that move at flow velocity and interact with neighbor particles within a set radius. No particles are allocated for the gas (air) phase.