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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.
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.
Working with Primary Atomization
Primary atomization refers to the process of forcing liquid through a small orifice at a high pressure, resulting in a fine spray of liquid droplets.

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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.
  - 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.
    - Lagrangian Phases
      A Lagrangian phase in Simcenter STAR-CCM+ is a dispersed phase (droplets, bubbles, or solid particles) modeled in a Lagrangian framework.
    - Parcels
      For flows involving a comparatively small number of dispersed phases, it is possible to formulate and solve governing equations for every droplet, bubble, or particle. However, if the number of dispersed phases is large, a statistical approach is more practical. In this approach, a smaller number of computational parcels represents the total population of dispersed phases.
    - Modeling Lagrangian Multiphase Flow
      To use the Lagrangian Multiphase model, you define the properties of the continuous and dispersed phases, their boundary conditions, their interactions, and their mode of injection.
    - Using the Lagrangian Multiphase Model with Time Models
      The Lagrangian Multiphase model is compatible with all Time models except Harmonic Balance.
    - Lagrangian Multiphase Reference
    - Lagrangian Phase Boundary Conditions
      The “boundary conditions” for a Lagrangian phase describe how particles behave when they impinge on a boundary.
    - Working with Primary Atomization
      Primary atomization refers to the process of forcing liquid through a small orifice at a high pressure, resulting in a fine spray of liquid droplets.
      - Atomization Models
        The atomization models simulate the breakup of a jet or a thin liquid sheet as it emerges from a spray injector.
    - Working with Secondary Breakup
      Liquid droplets sometimes break up under the action of non-uniform surface forces, a phenomenon that is known as secondary breakup.
    - Working with Injectors
      In Simcenter STAR-CCM+, particles enter the fluid continuum through injectors. While the Lagrangian phase defines what particles enter the domain and how they behave, the injector defines where, in what direction, and with what frequency, the particles enter.
    - Working with Particle Tracks
      A track records the history of a parcel.
    - Load Balancing for Lagrangian/Eulerian Flows
      For parallel processing, the traditional approach to decomposing the volume mesh is to give each processor approximately the same number of cells. For cases where the same Eulerian flow equations are solved in each cell, this approach generally gives good performance.
    - VOF-Lagrangian Phase Interaction Model Reference
      Lagrangian models track individual dispersed particles through the domain, while VOF Multiphase models track the volume fractions of two or more segregated phases. When using both modeling techniques (for example, water droplets spraying through the air into a large volume of water), you can link the two forms of modeling with a VOF-Lagrangian phase interaction model.
    - VOF-Lagrangian Stripping
      Lagrangian models track individual packets of finely dispersed particles through the domain, while VOF Multiphase models track the volume of two or more interpenetrating phases. When using both modeling techniques (for example, water droplets spraying through the air into a large volume of water), you can link the two forms of modeling with a Lagrangian Stripping model which is a type of phase interaction model.
    - Lagrangian/Eulerian Passive Scalar Interactions
      Lagrangian phases can interact both with other Lagrangian phases and with phases of other types using Multiphase Interaction models. Both Lagrangian and Eulerian frameworks give the option of using passive scalars as user-defined variables of arbitrary value, assigned to fluid phases or individual particles.
    - Lagrangian Multiphase Field Functions Reference
      This section describes the field functions that are made available to the simulation when the Lagrangian Multiphase model is used.
    - Post-Processing Lagrangian Data
      Simcenter STAR-CCM+ allows you to analyze the flow of Lagrangian phases through the containing fluid, and also the interaction of these phases with boundaries.
  - 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.

Working with Primary Atomization

Primary atomization refers to the process of forcing liquid through a small orifice at a high pressure, resulting in a fine spray of liquid droplets.

Depending on the internal construction of the injector, the liquid at the exit of an injector nozzle can be in the form of a thin liquid sheet or a jet. Simcenter STAR-CCM+ currently provides two models that simulate the atomization process of the liquid exiting the nozzle: the LISA model for the breakup of a thin liquid sheet that is produced with a pressure-swirl atomizer, and the Huh model for the breakup of a liquid jet created through a simple hole-type nozzle. Both types of injectors are grouped under the heading of "Nozzle Injector" that is defined by two basic parameter: orifice dimeter at nozzle exit and injector axis. Additional model-specific parameters are added according to the selected model.

What Is the Pressure-Swirl Atomizer?

The pressure-swirl atomizer, also commonly known as a simplex atomizer, is widely used for liquid-fuel injection in gas turbines, oil furnaces, and direct-injection spark-ignited automobile engines.

In this atomizer type, a swirling motion is imparted to the injected liquid through nozzles that are known as swirl ports. The liquid accelerates as it flows through the swirl ports into a central swirl chamber. Under the action of centrifugal force, it spreads out in the form of a conical sheet and develops a hollow air core. It emerges from the orifice as an unstable thinning liquid sheet, then breaking up into ligaments and then droplets. A sketch of a hollow-cone pressure swirl injector is shown in the figure below.

In the illustration above, three stages in the atomization process are identified: film formation, sheet breakup, and atomization. $δ_{o}$ is the initial film thickness in the nozzle; $2 h_{0}$ is the initial thickness of the film as it exits the nozzle, and $2 h_{b}$ is the thickness of the film at the point of breakup. $θ$ is the spray angle, which is defined as $0.5 \times (inner cone angle + outer cone angle)$ .