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Physics Simulation
Simcenter STAR-CCM+ can model a wide range of physics phenomena including fluid mechanics, solid mechanics, heat transfer, electromagnetism, and chemical reactions. Scenarios with multiple time scales can be solved within the same simulation.
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.
Eulerian Multiphase (EMP)
The Eulerian Multiphase (EMP) model in Simcenter STAR-CCM+ is based on an Eulerian-Eulerian formulation where each distinct phase has its own set of conservation equations.
Modeling Eulerian Multiphase Flow
You use the Eulerian Multiphase (EMP) flow model if the phases are expected to be mixed on length scales smaller than the length scales to resolve, or if both stratified and dispersed two-phase flow coexist in the flow domain. In this 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.
Modeling Bubbly and Droplet Flows
Bubbly and droplet flows are where one liquid or gas phase is dispersed within another liquid or gas phase throughout the domain at all times.
Modeling Potential Forces
Potential forces, such as capillary pressure and osmotic pressure, occur in a range of physical applications. The User-Defined Potential Force models a potential $Φ$ that applies to a Eulerian phase for a particular physical application.

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Physics Simulation
Simcenter STAR-CCM+ can model a wide range of physics phenomena including fluid mechanics, solid mechanics, heat transfer, electromagnetism, and chemical reactions. Scenarios with multiple time scales can be solved within the same simulation.
- Defining Physics Workflow
  Simcenter STAR-CCM+ contains a wide range of physics models and methods for the simulation of single- and multi-phase fluid flow, heat transfer, turbulence, solid stress, dynamic fluid body interaction, aeroacoustics, and related phenomena. These physics models are all selected using a physics continuum.
- Setting Up Physics
  This section provides information on how to set up physics models in STAR-CCM+.
- Running Physics Simulations
  This part of the documentation describes preparation and procedures for running a Simcenter STAR-CCM+ simulation.
- Motion
  In general, motion can be defined as the change in position of a body with respect to a certain reference frame.
- Space
  The primary function of the Space models in Simcenter STAR-CCM+ is to provide methods for computing and accessing mesh metrics. Examples of mesh metrics include cell volume and centroid, face area and centroid, cell and face indexes, and skewness angle.
- Time
  The primary function of the time models in Simcenter STAR-CCM+ is to provide solvers that control the iteration and/or unsteady time-stepping.
- Mesh Motion and Adaption
  Many simulations that involve motion or geometry change require you to move or deform the mesh. Other simulations require localized mesh adaption in order to achieve an accurate solution.
- Materials
  Material models simulate substances, including various mixtures.
- Fluid Flow
  Many engineering design projects require you to predict the effect of flowing fluids on containing structures or immersed objects. While you can analyse simple scenarios with hand calculations, complex scenarios require you to apply numerical methods for accurate solutions.
- Viscous Flow
  Viscous Flow is a finite element approach for use with viscoelastic materials and other highly viscous non-Newtonian fluids, such as liquid plastics and rubber, dough and similar foodstuffs, molten glass, and mud. Viscoelastic materials resemble elastic materials, but also exhibit viscous effects, rebounding slowly from deformations.
- Passive Scalars
  Passive scalars are user-defined variables of arbitrary value, assigned to fluid phases or individual particles. They are passive because they do not affect the physical properties of the simulation. An intuitive way to think of passive scalars is as tracer dye in a fluid, but with numerical values instead of colors, and with no appreciable mass or volume.
- Heat Transfer
  Heat transfer is the study of energy in transit due to a temperature difference in a medium or between media. Heat transfer extends thermodynamic analysis through the study of the modes of energy transfer and through development of relations to calculate energy transfer rates.
- Species
  This chapter provides information about the chemical species models in Simcenter STAR-CCM+. A species model is activated whenever a multi-component liquid or multi-component gas is chosen from the Material model section of the Physics Model Selection dialog.
- Porous Media
  Simcenter STAR-CCM+ allows you to simulate the transport of a fluid or energy (e.g. heat, electrical charge) through porous materials using the concept that the action of the porous media can be represented using appropriate loss (or 'diffusion') coefficients.
- Adjoint
  The adjoint method is an efficient means to predict the influence of many design parameters and physical inputs on some engineering quantity of interest, that is, on the engineering objective of the simulation. In other words, it provides the sensitivity of the objective (output) with respect to the design variables (input).
- Fans and Blowers
  Simcenter STAR-CCM+ provides models for axial and radial fans where classical fan laws apply.
- Virtual Disk Model
  The virtual disk model is based upon the principle of representing propellers, turbines, rotors, fans, and so on, as an actuator disk. The actuator disk treatment is practical when you are concerned about the influence of the rotor/propeller behavior on the flow rather than knowing about the detailed interactions between the flow and the blades of the rotating device.
- Turbulence
  Most fluid flows of engineering interest are characterized by irregularly fluctuating flow quantities.
- Transition
  The term transition refers to the phenomenon of laminar to turbulence transition in boundary layers. A transition model in combination with a turbulence model predicts the onset of transition in a turbulent boundary layer.
- Wall Distance
  Wall distance is a parameter that represents the distance from a cell centroid to the nearest wall face with a non-slip boundary condition. Various physical models require this parameter to account for near-wall effects.
- Radiation
  The Radiation Model is the gateway, or entry point to all of the radiation modeling capabilities of Simcenter STAR-CCM+. This section describes Simcenter STAR-CCM+’s radiation modeling.
- Aeroacoustics
  Aeroacoustics investigates the aerodynamic generation of sound.
- Reacting Flow
  Simcenter STAR-CCM+ provides a selection of models that you can use to simulate a wide range of reacting flow applications.
- Internal Combustion Engines
  In an internal combustion engine (ICE), for example a gasoline engine, the process of combustion takes place in a cylinder (or cylinders) within the engine. The working fluid is a fuel and oxidizer mixture (usually air), which reacts to form combustion products.
- 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.
  - Multiphase Framework
    In mathematical terms, there are two main frameworks in the formulation of the multiphase models in Simcenter STAR-CCM+, the Eulerian and Lagrangian modeling strategies.
  - Multiphase Simulation Concepts
    This section presents the key concepts you come across when using the Simcenter STAR-CCM+ multiphase models.
  - 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.
  - Defining Eulerian Phases
    A Eulerian phase in Simcenter STAR-CCM+ represents a distinct physical substance – the phase material – that is modeled in a Eulerian framework. Two materials constitute two different Eulerian phases. The definition of a Eulerian phase includes the set of models that apply to the phase material and the relevant material properties.
  - Defining Phase Interactions
    A phase interaction is an object that defines the choice of models that are used to predict the influence of one phase upon another phase within a multiphase flow simulation. Define a phase interaction for every possible significant coupling.
  - Discrete Element Method (DEM)
    The Discrete Element Method (DEM) is an engineering numerical method to simulate motion of many interacting discrete objects that are typically solid particles. Although DEM modeling demands significant computing power, it provides detailed resolution that other methods cannot achieve. In Simcenter STAR-CCM+, DEM can be applied to regions with or without a volume mesh.
  - Dispersed Multiphase (DMP)
    The Dispersed Multiphase (DMP) model simulates dispersed phases in a Eulerian manner. The Dispersed Multiphase model combines aspects of both the Lagrangian Multiphase (LMP) model and the Eulerian Multiphase (EMP) models.
  - Eulerian Multiphase (EMP)
    The Eulerian Multiphase (EMP) model in Simcenter STAR-CCM+ is based on an Eulerian-Eulerian formulation where each distinct phase has its own set of conservation equations.
    - Boiling
      The Wall Boiling and Bulk Boiling models within the Eulerian Multiphase framework of Simcenter STAR-CCM+ are aimed at forced-convection, subcooled, boiling applications.
    - Particle Size Distributions
      Particle size is a vital parameter for calculating particle hydrodynamics in dispersed multiphase flows.
    - Modeling Eulerian Multiphase Flow
      You use the Eulerian Multiphase (EMP) flow model if the phases are expected to be mixed on length scales smaller than the length scales to resolve, or if both stratified and dispersed two-phase flow coexist in the flow domain. In this 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.
      - Modeling Bubbly and Droplet Flows
        Bubbly and droplet flows are where one liquid or gas phase is dispersed within another liquid or gas phase throughout the domain at all times.
        Modeling Droplet Evaporation
        The Droplet Evaporation Rate models account for mass transfer due to evaporation and condensation.
        Modeling Dissolution Mass Transfer
        For Eulerian multi-component multiphase flows, transfer between the components of each phase can occur. The Dissolution Mass Transfer Rate model includes the case where one phase is liquid and one phase is gaseous, and the case where both phases are liquid.
        Modeling Interphase Reactions
        Mass transfer can be modeled as a reaction between two multi-component Eulerian phases, usually one liquid and one gas phase.
        Modeling Emulsions
        An emulsion is a dispersion of small droplets of one liquid in another liquid, where the droplets are not soluble or miscible. To model the non-Newtonian viscosity of such a fluid, use the Emulsion Rheology model.
        Modeling Potential Forces
        Potential forces, such as capillary pressure and osmotic pressure, occur in a range of physical applications. The User-Defined Potential Force models a potential $Φ$ that applies to a Eulerian phase for a particular physical application.
        Example: Modeling Capillary Pressure in Foam Drainage
        You can model capillary pressure with the User-Defined Potential Force. An example application, modeling foam drainage, is presented.
        Example: Modeling Flow in a Porous Medium
        You can model capillary pressure with the User-Defined Potential Force. An example application, modeling flow in a porous medium, is presented.
      - Modeling Multiple Flow Regimes
        The Multiple Flow Regime Phase Interaction model is used for cases where both segregated and dispersed two-phase flows exist in the same domain. An example scenario is a flow of a liquid and gas under undulating motion.
      - Modeling Particulate Flows
        Particulate flows describe multiphase flow regimes that deal with gas-solid or liquid-solid flows. Examples of these flows are fluidized beds, pneumatic conveyors, and cement.
      - Modeling Mixture Turbulence
        You can model the effects of turbulence on the multiphase mixture.
      - Modeling Boiling
        The boiling models can be used for forced-flow, subcooled boiling applications.
      - Modeling Adaptive Multiple Size-Group Particle Size Distribution
        To correctly simulate the flow behavior in dispersed multiphase flows, you must account for the particle size distribution.
      - Modeling S-Gamma Particle Size Distribution
        To correctly simulate the flow behavior in dispersed multiphase flows, you must account for the particle size distribution.
      - Modeling Phasic Turbulence
        You can model the effects of turbulence on both the continuous and dispersed phases.
      - Setting Boundary Conditions
        You specify the boundary conditions and values for each phase.
      - Setting the Solver Parameters
        Set the solver parameters. The under-relaxation factors are important and are common to all solvers. The other settings are typically used for troubleshooting.
    - Physics Models Reference
  - Fluid Film
    Problems where a thin film of fluid exists on solid boundaries are common in engineering practice. Examples include fluid film on the internal surfaces of automotive engines, gas turbines, spray-cooling systems and ink-jet printers.
  - Lagrangian Multiphase (LMP)
    A wide variety of flow processes involve the transport of solid particles, liquid droplets, or gas bubbles—known as dispersed phases—by a gaseous or liquid continuous phase.
  - Mixture Multiphase (MMP)
    In the Mixture Multiphase (MMP) model, mass, momentum, and energy are treated 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. The model is computationally more efficient than models that simulate each phase separately.
  - Resolved Transition
    Simcenter STAR-CCM+ provides the Resolved Transition model as a phase interaction model, which lets you capture the breakup of pools of liquid to form droplets emerging/stripping from a free surface or small bubbles stripped from a large bubble. This model is meant to be used as part of a hybrid multiphase approach where the Volume of Fluid (VOF) model or Mixture Multiphase (MMP) model is used alongside the Lagrangian Multiphase (LMP) model.
  - Smoothed-Particle Hydrodynamics (SPH)
    Smoothed-Particle Hydrodynamics (SPH) is a numerical method that overcomes the volume meshing-related constraints occurring with mesh-based models. SPH represents the fluid as a collection of particles with material properties that move with the fluid, making it well-suited for applications with highly dynamic free-surface flows.
  - Two-Phase Thermodynamic Equilibrium
    The Two-Phase Thermodynamic Equilibrium is a multiphase mixture approach that is restricted to modeling two phases. With this model Simcenter STAR-CCM+ solves the mass, momentum, and energy as mixture quantities rather than phase quantities. Therefore, the computational efforts are reduced by assuming the suspension to be a homogeneous single-phase system.
  - Volume Of Fluid (VOF) Multiphase
    The Volume Of Fluid (VOF) Multiphase model is a simple multiphase model. It is suited to simulating flows of several immiscible fluids on numerical grids capable of resolving the interface between the phases of the mixture.
  - Modeling VOF Waves
    The VOF Waves model is used to simulate surface gravity waves on the interface between a light fluid and a heavy fluid. This model is typically used with the 6-DOF Motion model for marine applications.
- Dynamic Fluid Body Interaction
  Dynamic Fluid Body Interaction (DFBI) in Simcenter STAR-CCM+ allows you to simulate the motion of a 6-DOF body with the displacement and rotation resulting from the defined mechanical and multiphysics interaction (flow, DEM, solid stress, EMAG).
- Harmonic Balance
  Some unsteady flows have a regularly repeating flow pattern, that is, they are time-periodic. Consider the flow from a fan blade passing across the entrance to a duct. Measurements of the instantaneous flow just within the duct would show a regularly repeating pattern. If the flow disturbances are sufficiently large, and propagate to the end of the duct, measurements of the unsteady flow at any point within the duct show repeating patterns. Such time-periodic patterns can be expressed using Fourier series.
- Solid Stress
  Simcenter STAR-CCM+ allows you to model the response of a solid continuum to applied loads, including mechanical loads and thermal loads that result from changes in the solid temperature.
- Electromagnetism
  Simcenter STAR-CCM+ allows you to model engineering applications involving electromagnetic phenomena. Example applications are electric motors, electric switches, and transformers, which can be modeled based on the classical theory of Electromagnetism.
- Electrochemistry
  Electrochemistry is the study of chemical reactions which occur due to an imposed electrical charge, or a difference in electrical potential at a boundary between a conductor–such as a metal–and an electrolyte. Simcenter STAR-CCM+ provides models that allow you to simulate batteries, corrosion, etching, and other electrochemical reactions.
- Electric Circuits
  Electrical circuits are conducting loops of interconnected electrical components, such as batteries, power sources, resistors, and inductors.
- Plasma
  Plasma is a state of matter similar to a gas that is composed partially or completely of charged particles such as ions and electrons which are not bound to each other.
- Batteries
  You can simulate batteries in Simcenter STAR-CCM+ using battery cells and battery cycling procedures that are defined either directly in Simcenter STAR-CCM+, or in the external software package Simcenter Battery Design Studio.
- Casting
  Casting simulations are performed using transient multiphase simulations using the VOF model with solidification. Conjugate heat transfer is applied between the solidifying melt and the solid mold.
- Region Sources
  This section provides some guidelines on how to use region sources for some common problems.
- Cell Quality Remediation
  The Cell Quality Remediation model helps you get solutions on a poor-quality mesh. This model identifies poor-quality cells, using a set of predefined criteria, such as Skewness Angle exceeding a certain threshold. Once these cells and their neighbors have been marked, the computed gradients in these cells are modified in such a way as to improve the robustness of the solution.
- Guidelines for Applying Simcenter STAR-CCM+
  This part of the documentation provides guidelines on applying Simcenter STAR-CCM+ models to your applications.
- Common Solvers Reference
  In Simcenter STAR-CCM+, solvers compute the solution during the simulation run.

Modeling Potential Forces

Potential forces, such as capillary pressure and osmotic pressure, occur in a range of physical applications. The User-Defined Potential Force models a potential $Φ$ that applies to a Eulerian phase for a particular physical application.

For illustrations of how the model can be used in different applications, refer to the following examples:

The User Potential Force model is available in a two-phase Eulerian Multiphase (EMP) simulation with one gas phase and one liquid phase.

The steps in this procedure are intended to follow on from Step 1 in Modeling Bubbly and Droplet Flows.

To model potential forces:

In the liquid phase, open the Phase Model Selection dialog and then, in the Optional Models group box, select User Potential Force.
Specify the User Potential.

The potential can be a function of the volume fraction $α$ and/or other scalars.

See User Potential Properties.
Specify the User Potential Force Prefactor.

See User Potential Force Prefactor Properties.
Specify the User Potential Volume Fraction Derivative.

This value is used for linearization only so there is no requirement for an exact expression. Excessive linearization can slow down the convergence rate, so you are recommended to use the default value $\frac{\partial Φ}{\partial α} = 0$ . However, if the driving force is strong compared to other forces, it can lead to checker-boarding and instability. In these cases, the linearization stabilizes the calculations.

See User Potential Volume Fraction Derivative Properties.
In the phase interaction, set the Drag Force model to use the Field Function (Linearized Coefficient) method.

Return to Modeling Bubbly and Droplet Flows and continue with Step 2.