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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.
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.
Viscous Flow Reference
This section describes the physics models specific to viscous flow.
Conservative Level-Set Model Reference
Level set method [reflink] is an interface capturing technique that uses a scalar field to track the interface between fluids. The method assigns a phase indicator function $φ_{i} (x, t)$ to each fluid in the system, denoting the regions of the domain occupied by the $i$ th phase at point $x$ and time $t$ . This is conceptually similar to a tracer dye or a passive scalar function. Conservative level set conserves fluid volume across interfaces.

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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.
  - Modeling Rheology
    Rheology distinguishes materials with "memory" from those without.
  - Setting Up Viscous Fluid Flow
    The workflows for setting up viscous flow simulations of different constitutive models are similar. To model a non-Newtonian fluid with a high viscosity or a variable viscosity depending on shear-rate without any elastic effects, choose the Generalized Newtonian Model. If the fluid exhibits time-dependent, shear thinning behavior, choose the Thixotropic Model. If the fluid exhibits normal stress or memory effects, work with the Viscoelastic Model. High shear rates in the flow can lead to a temperature increase—viscous heating. To account for this effect, Simcenter STAR-CCM+ provides the Viscous Energy Model.
  - Setting Up Viscous Multiphase Flow
    You can use the Viscous Multiphase model to simulate extrusion or co-extrusion applications.
  - Extrusion and Free Surface Flow
    You can use the Free Surface model to simulate extrusion processes of polymer melts and other processes involving free surface flow of generalized Newtonian and viscoelastic fluids. A free stream boundary represents the outer surface of the extrudate, and an internal interface identifies the boundary between extrudates in contact. Since its shape is not known at the start of the simulation, the free surface is calculated as part of the solution. Typically, you set up these simulations as steady-state. You can also use time-dependent simulations, in which case the free surface position propagates at the material velocity.
  - Setting Up Extrusion and Free Surface Flow
    Use the following steps for each extrudate continuum in the simulation. This workflow applies to steady-state extrusion simulations where the extrudate length is pre-defined.
  - Setting Up a Film Casting Simulation
    Film casting is modeled as a free-surface flow with a two-dimensional mesh, for a thin film of one or more layers of viscoelastic fluids extruded into free space.
  - Setting Up a Compression Molding Simulation
    Compression molding is a common production processes using polymeric, plastic, or composite parts. The initial charge can contain short or long fibers to produce short-fiber reinforced composites or sheet molding compounds (SMC). Compression molding is modeled with the Partial Fill and Free Surface models. The simulation starts with an initial charge of polymer placed in an open, heated cavity. The cavity is then closed and compressed to force the material to fill the cavity.
  - Viscous Flow Reference
    This section describes the physics models specific to viscous flow.
    - Viscous Flow Model Reference
      The Viscous Flow model is the prerequisite for all viscous flow simulations.
    - Rheology Models Reference
      The available rheology models for viscous flow are the Generalized Newtonian, Viscoelastic, and Thixotropic models.
    - Free Surface Model Reference
      The Free Surface model allows for the simulation of movement and change of shape in the surface of a viscous liquid. This model is supported for both single and multiphase flows.
    - Partial Fill Model
      The Partial Fill model allows the simulation of viscous flows moving in a region they do not fully occupy. It facilitates simulation of injection molding, mixing, and compounding.
    - Surface Tension Model
      The Surface Tension model allows the simulation of the surface tension force at a free fluid surface, including open fluid surfaces (as in partial filling) and the surfaces between two fluids (as in co-extrusion).
    - Viscous Energy Model
      The Viscous Energy model simulates the energy that drives the expansion of a viscous fluid due to shear stress.
    - Viscous Radiation Model Reference
      The Viscous Radiation model enables thermal boundary conditions at walls and free stream boundaries that account for radiation fluxes.
    - Film Casting Model
      The Film Casting model simulates a thin film of viscoelastic fluid extruded into free space. It can be used for both single-layer and multilayer film casting.
    - Material Calibration Model Reference
      This model takes input tables of experimental rheological data and performs material calibration curve fitting on the data, and fills in the model parameters for a generalized Newtonian model, a viscoelastic fluid model, or the Chemorheology model based on the curve derived from the data.
    - Short Fiber Orientation Model Reference
      The Short Fiber Orientation model describes the flow properties of short fibers suspended in a viscous fluid, including their change in mean orientation in response to the fluid flow. This model is supported for both single and multiphase flows.
    - Fiber-Flow Interaction Model
      This model simuates two-way coupling between viscous fluid and short fibers suspended in it. Interaction with the fibers alters flow field variables in addition to the flow altering fiber orientation.
    - Chemorheology Model Reference
      The Chemorheology model simulates the behavior of fluids that change their rheological properties due to an underlying curing process. This model is supported for both single and multiphase flows.
    - Viscous Multiphase Model Reference
      The Viscous Multiphase model allows the simulation of several distinct and immiscible viscous phases in a single continuum.
    - Conservative Level-Set Model Reference
      Level set method [reflink] is an interface capturing technique that uses a scalar field to track the interface between fluids. The method assigns a phase indicator function $φ_{i} (x, t)$ to each fluid in the system, denoting the regions of the domain occupied by the $i$ th phase at point $x$ and time $t$ . This is conceptually similar to a tracer dye or a passive scalar function. Conservative level set conserves fluid volume across interfaces.
  - Mesh Requirements and Guidelines
    As the Viscous Flow Solver uses a Finite Element (FE) approach, the volume mesh must meet certain requirements.
  - Guidelines for the eXtended Pom-Pom Model (XPP)
    The eXtended Pom-Pom (XPP) model applies to complex flows of branched polymers (the "pom-poms") with significant shear flow and extension. To enhance convergence of simulations that use the XPP model, you are advised the following:
  - Viscous Flow Field Function Reference
    The following primitive field functions become available with the activation of viscous flow models. The models required are noted in each entry.
- 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.
- 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.

Conservative Level-Set Model Reference

Level set method [275] is an interface capturing technique that uses a scalar field to track the interface between fluids. The method assigns a phase indicator function $φ_{i} (x, t)$ to each fluid in the system, denoting the regions of the domain occupied by the $i$ th phase at point $x$ and time $t$ . This is conceptually similar to a tracer dye or a passive scalar function. Conservative level set conserves fluid volume across interfaces.


Theory	See Conservative Level Set
Provided By	[physics continuum] > Models > Viscous Multi-Phase Model
Example Node Path	Continua > Physics 1 > Models > Conservative Level-Set
Requires	Material: Multiphase Multiphase Model: Viscous Multiphase
Properties	Key properties are: Diffusion Exponent, Reinitialization Penalty Factor, Lagrange Multiplier Moment. See Conservative Level-Set Model Properties.

Conservative Level-Set Model Properties

Diffusion Exponent: $d$ in Eqn. (1085). The default value is 0.1.
Reinitialization Penalty Factor: Governs how aggressively the reinitialization step of the conservative level set is imposed. The default value is 2. Greater values may result in more accurate values for the phase fields near the interface but can simultaneously cause issues with the convergence of the simulation.
Lagrange Multiplier Moment: $p$ in Eqn. (1081). For simulations with more than two fluids ( $n > 3$ ), higher values of $p$ can improve convergence. The default value is 2.