Multiphase Flow

Multiphase flow is a term which refers to the flow and interaction of several phases within the same system where distinct interfaces exist between the phases. Simcenter STAR-CCM+ considers flow options where phases coexist as: gas bubbles in liquid, liquid droplets in gas, and/or solid particles in gas or liquid, and/or (large scale) free surface flows.

The term ‘phase’ usually refers to the thermodynamic state of the matter: solid, liquid, or gas. In modeling terms, a phase is defined in broader terms, and can be defined as a quantity of matter within a system that has its own physical properties to distinguish it from other phases within the system. For example:

Liquids of different density
Bubbles of different size
Solid granules of different size and/or weight

Multiphase flows are different from multi-component flows. In multi-component flows, the different species are mixed at the molecular level. These species have the same convection velocity. In multiphase flows, the different phases are mixed at the macroscopic scale. These phases have different convection velocity. Many flows are multiphase multi-component flows.

Multiphase flows can be classified into two categories:

Dispersed flows, such as bubbly, droplet, and particle flows
Stratified flows, such as free surface flows, or annular film flow in pipes.

A phase is considered dispersed if it occupies disconnected regions of space—otherwise it is continuous.

Simcenter STAR-CCM+ provides the following distinct multiphase models to meet the requirements of the two main categories of flow:


Model	Key Applications	Example Applications
Dispersed Multiphase (DMP) Simulates flows of low loadings of particles dispersed in a continuous phase (dilute multiphase mixture) in a Eulerian manner. Provides a lightweight alternative to the Lagrangian Multiphase model. The conservation equations for mass, momentum, and energy are solved for each dispersed phase. The transport equations of the continuous phase are solved by a single phase model. The DMP model is suitable for dispersed flows of droplets, bubbles, and solid particles with low volume fraction of the dispersed phase.	Automotive Soiling Aerospace Icing Wet steam in low pressure steam turbine stages
Eulerian Multiphase (EMP) This model, based on the concept of interpenetrating continua, solves conservation equations for mass, momentum, and energy for each phase. The phases share the pressure field and the inter-phase interactions need to be modeled to close the set of equations. Phase interaction models are provided to define the influence that one phase exerts upon another across the interfacial area between them. The EMP model is used to model the dispersed flows of bubbles, droplets, solid particles, and for modeling a combination of dispersed and stratified flows.	Bubble Columns Mixing Vessels Settling Tanks Fluidized Beds Multiphase Separators Stepped Spillway Multiphase Pumps Phase Change equipments
Fluid Film Predicts the dynamic characteristics of wall films using boundary layer approximations and assumed velocity and temperature profiles across the depth of the film. Film transport is predicted using thin shells that lie across the surface of solid walls on which the film is formed. The Fluid Film model is suitable for stratified thin liquid film flows over surfaces.	Vehicle Rainwater Management Selective Catalytic Reduction (SCR) Fuel Sprays Lubrication Spray Coating/Deposition Aircraft Ice Protection
Mixture Multiphase (MMP) A simplified multiphase model that can be used to model the flow of miscible phases. In this model, the computational efforts are reduced by assuming the multiphase mixture to be a homogeneous single-phase system for which only one set of transport equations is solved. The MMP model is suitable for dispersed flows of mixtures of bubbles in liquid or droplets in gas.	Partially resolved gearbox/tank sloshing Multiphase pumps Fuel Cells Boilers Steam generators
Two-Phase Thermodynamic Equilibrium A simplified multiphase mixture implementation, which is designed for applications that involve two phases of the same substance, typically water and steam, which are in thermodynamic equilibrium. The Two-Phase Thermodynamic Equilibrium model is suitable for dispersed flows of two thermodynamic phases of the same material.	Steam Generators Boilers Steam Turbines
Volume Of Fluid (VOF) Multiphase Provided for systems containing two or more immiscible fluid phases, where each phase constitutes a large structure within the system (such as typical free surface flows). This approach captures the movement of the interface between the fluid phases, and is often used for marine applications. The VOF model is suitable for stratified flows (free surfaces).	Marine Hydrodynamics and Seakeeping Fuel Tank Sloshing Oil and Gas Flow Assurance IC Engine Cooling
Discrete Element Method (DEM) This model is an extension of the Lagrangian framework. Individual particles are modeled rather than representative parcels and inter-particle contact forces are explicitly accounted for. DEM is used to model densely packed granular flows where particle shape and collision behavior are important. The DEM model is suitable for dispersed flows of discrete solid particles with high volume fraction of the particles.	Fluidized beds Rock mechanics Conveying aggregates Tablet coating Plugging fissures in oil wells Crop harvesting and lawn mowing
Smoothed-Particle Hydrodynamics (SPH) SPH is a numerical method that overcomes meshing-related constraints occurring with mesh-based models, while still being based on the Navier-Stokes equations. Due to its Lagrangian characteristic and particle approach, the SPH method can model a wide range of applications involving dynamic flows with complex interfaces. SPH is particularly well-suited for fast dynamic flows and complex boundaries, including interfaces with fragmentations and reconnections such breaking waves, jets and splashes, and moving parts.	Powertrain lubrication with oil bath Sloshing
Lagrangian Multiphase (LMP) Solves the equation of motion for representative parcels of the dispersed phase as they pass through the system. For the continuous phase, the conservation equations for mass, momentum, and energy are solved. It is intended for systems that consist mainly of a single continuous phase carrying a relatively small volume of solid discrete particles, droplets, or bubbles. It is suited where the interaction of the discrete phase with physical boundaries is important. The LMP model is suitable for dispersed flows of discrete particles (bubbles, droplets, solid particles) with low volume fraction of the particles.	Vehicle Water Management Cyclone Separation Erosion Aerosol Dispersion Liquid Fuel Combustion Spray Cooling Spray Coating

Simcenter STAR-CCM+ provides a selection of multiphase and phase interaction models to simulate a wide range of multi-regime and multi-scale multiphase flows. In addition, hybrid modeling can be used to model multiple flow regimes of a phase material by using a combination of several different multiphase models.

A common framework has also been developed to specify the models that define how pairs of phases interact with each other. These models are known as phase interactions.

The multiphase models can also be used with the complementary technologies available in Simcenter STAR-CCM+, such as the population balance modeling to predict the size distribution of the dispersed phase, adaptive mesh refinement (AMR) for providing a solution-refined mesh, and adaptive time-stepping for automatic time-step adjustments.