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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.
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.
Defect Prediction Using Criteria Functions
Criteria functions are post-processing items to help predict casting defects like macro- or micro-porosity and to estimate relevant microstructural quantities such as primary and secondary dendrite arm spacings.
Criteria Functions Definitions
Niyama Criterion
The scalar quantity Niyama Criterion estimates the porosity probability from the ratio between the shrinkage rate and the feeding distance.

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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.
- 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.
  - Selecting the Physics Models for the Melt
    You select the multiphase models, a laminar flow regime, and the casting model.
  - Selecting the Physics Models for the Mold
    The mold is a solid material. To investigate the heat transfer in the mold, you activate the solution of the energy equation in the solid. Optionally, you can take radiation into account.
  - Selecting the Pure Thermal Model
    A pure thermal simulation simulates only the solidification process of the melt. The solution of the flow equations is de-activated and only the solution of the energy equation is activated. This simulation type lets you analyze the behavior of the solidifying melt with respect to temperature without any flow.
  - Selecting the Variable Density Compensation Model
    You use the variable density compensation model for any solid region with a non-constant solid density. The variable density compensation model applies the corrective energy source term. The corrective energy source is a source term that compensates the changes of the system mass in the energy transport equation due to shrinkage of a solidifying part with temperature-dependent density.
  - Working With the Casting Material Database
    The accuracy of a casting simulation depends on the quality and completeness of the material data that you use. Therefore, a database that contains certified and qualified property data for casting is essential for high quality casting simulations.
  - Importing Casting Materials and Properties in Simcenter STAR-CCM+ From an External File
    You can import casting materials and properties into the Simcenter STAR-CCM+ Material Database. You can then use the materials in a physics continuum, and use the material properties as boundary values.
  - Detecting Shrinkage-Related Defects
    You can use the Macro Porosity model to detect shrinkage-related defects in a cast part. When isolated liquid melt regions occur during the solidification process of a cast part, shrinkage cannot be compensated for by supplying extra melt, and pores form.
  - Defect Prediction Using Criteria Functions
    Criteria functions are post-processing items to help predict casting defects like macro- or micro-porosity and to estimate relevant microstructural quantities such as primary and secondary dendrite arm spacings.
    - Setting Up a Criteria Function
      You select the particular criteria function that you require as a phase interaction model.
    - Criteria Functions Definitions
      - Liquid Residence Time
        The fluid enters the computational domain in a liquid state with a temperature above the solidus temperature. The Liquid Residence Time is the time between the fluid entering the computational domain and the moment that the temperature decreases below the solidus temperature.
      - Solidification Time
        The Solidification Time is the time that is taken to cool down the VOF phase from liquidus temperature to solidus temperature.
      - Local Solidification Time
        The scalar quantity Local Solidification Time is collected for all specified Criteria Temperatures below the liquidus temperature. The Local Solidification Time is the value of the Solidification Time passive scalar in the cell at the moment the temperature decreases below the respective Criteria Temperature.
      - Cooling Rate
        The scalar quantity Cooling Rate is the time derivative of temperature. The cooling rate is computed for all specified Criteria Temperatures.
      - Isotherm Speed
        The scalar quantity Isotherm Speed is an approximation of the propagation velocity of the isotherm at the respective Criteria Temperature.
      - Temperature Gradient
        The vector quantity Temperature Gradient $Δ T |_{T_{c r i t}}$ is the spatial derivative of temperature. It is computed for all specified Criteria Temperatures.
      - Mean Cooling Rate
        The scalar quantity Mean Cooling Rate is the average cooling rate over the entire solidification process.
      - Solidification Velocity
        The vector quantity Solidification Velocity is an approximation for the velocity of the solidification front. This quantity is computed for all specified Criteria Temperatures.
      - G/v
        The scalar quantity G/v is the ratio between the temperature gradient $G$ and the solidification velocity $v$ and is an important measure for the resulting micro structure.
      - Niyama Criterion
        The scalar quantity Niyama Criterion estimates the porosity probability from the ratio between the shrinkage rate and the feeding distance.
      - Dimensionless Niyama Criterion
        You can use the dimensionless Niyama criterion to directly predict the amount of shrinkage porosity during solidification of metal alloy castings.
      - Primary Dendrite Arm Spacing
        The scalar quantity primary dendrite arm spacing (also referred to as PDAS or DAS) is the distance between the axes of the dendrites. This quantity is computed only for liquidus temperature.
      - Secondary Dendrite Arm Spacing (LST)
        The scalar quantity Secondary Dendrite Arm Spacing (LST) (also referred to as SDAS-LST) is the distance between the arms of dendrites. This quantity is computed for all specified Criteria Temperatures.
      - Secondary Dendrite Arm Spacing (CR)
        The scalar quantity Secondary Dendrite Arm Spacing (CR) (also referred to as SDAS-CR) is the distance between the arms of dendrites. This quantity is computed for all specified Criteria Temperatures.
    - Criteria Functions Properties
      You specify the critical temperatures between the solidus and liquidus temperatures at which Criteria Functions are evaluated.
  - Artificial Compressibility
    Typically, for casting simulations, the gas phase is considered to be compressible and the ideal gas law is applied. The melt is a liquid and has a constant density. Therefore, the multiphase mixture is not compressible throughout the entire computational domain. This inhomogeneity results in regions with finite and infinite speeds of sound, which can lead to numerical instabilities and convergence problems.
  - Casting Field Functions
    The following primitive field functions are available to the casting simulation.
  - Casting Bibliography
- 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.

Niyama Criterion

The scalar quantity Niyama Criterion estimates the porosity probability from the ratio between the shrinkage rate and the feeding distance.

The shrinkage rate is assumed to be proportional to the Solidification Velocity and the feeding distance is assumed to be proportional to the Temperature GradientGradient. The criterion is computed for all Critical Temperatures.

Figure 1. EQUATION_DISPLAY

K_{Niyama} = \frac{\nabla T |_{T_{c r i t}}}{\sqrt{- \dot{T} |_{T_{c r i t}}}}

(367)

The Niyama Criterion predicts central porosity areas that appear as a result of melt contraction in the last stages of solidification. This criterion applies to low-carbon steel alloys. The critical value of this criterion, below which shrinkage defects form, is determined experimentally.