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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.
Turbulence
Most fluid flows of engineering interest are characterized by irregularly fluctuating flow quantities.
Reynolds-Averaged Navier-Stokes (RANS) Turbulence Models
RANS turbulence models provide closure relations for the Reynolds-Averaged Navier-Stokes equations, that govern the transport of the mean flow quantities.
Spalart-Allmaras Turbulence
The Spalart-Allmaras turbulence model is a one-equation model that solves a transport equation for the modified diffusivity $\tilde{ν}$ in order to determine the turbulent eddy viscosity.
Deciding on a Spalart-Allmaras Model
To choose the appropriate model and wall treatment for your application take into account the following recommendations:

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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.
  - Selecting a Turbulence Modeling Approach
    Selecting the turbulence modeling approach is possible with or without auto-select.
  - Reynolds-Averaged Navier-Stokes (RANS) Turbulence Models
    RANS turbulence models provide closure relations for the Reynolds-Averaged Navier-Stokes equations, that govern the transport of the mean flow quantities.
    - Deciding on a RANS Turbulence Model
      There are four major classes of RANS turbulence models currently in Simcenter STAR-CCM+. This section presents broad guidelines as to the applicability of each of these.
    - Spalart-Allmaras Turbulence
      The Spalart-Allmaras turbulence model is a one-equation model that solves a transport equation for the modified diffusivity $\tilde{ν}$ in order to determine the turbulent eddy viscosity.
      - Deciding on a Spalart-Allmaras Model
        To choose the appropriate model and wall treatment for your application take into account the following recommendations:
      - Accounting for Anisotropy of Turbulence
      - Spalart-Allmaras Model Reference
        The Standard Spalart-Allmaras model allows you to compute the modified diffusivity $\tilde{ν}$ to provide closure to the Reynolds-Averaged Navier-Stokes equations.
      - Spalart-Allmaras Initial Conditions Reference
        This section details the conditions and values that are required for initialization of the Standard Spalart-Allmaras turbulence model.
      - Spalart-Allmaras Boundaries Reference
        This section details the conditions that are required for each boundary type that is supported by the Standard Spalart-Allmaras turbulence model. In addition, information is provided about the values for each boundary type.
      - Spalart-Allmaras Regions Reference
        This section details the conditions that are required for each region type that is supported by the Standard Spalart-Allmaras turbulence model. In addition, information is provided about the values for each region type.
      - Spalart-Allmaras Solvers Reference
        This section details the solvers that are associated with the Standard Spalart-Allmaras turbulence model: turbulence and turbulent viscosity.
      - Spalart-Allmaras Field Functions Reference
        This section details the field functions that are made available to the simulation when the Standard Spalart-Allmaras turbulence model is used.
    - K-Epsilon Turbulence
      The K-Epsilon turbulence model is a two-equation model that solves transport equations for the turbulent kinetic energy $k$ and the turbulent dissipation rate $ε$ in order to determine the turbulent eddy viscosity.
    - K-Omega Turbulence
      The K-Omega turbulence model is a two-equation model that solves transport equations for the turbulent kinetic energy $k$ and the specific dissipation rate $ω$ —the dissipation rate per unit turbulent kinetic energy ( $ω \propto ε / k$ )—in order to determine the turbulent eddy viscosity.
    - Reynolds Stress Transport (RST) Turbulence
      Reynolds Stress Transport (RST) models, also known as second-moment closure models, directly calculate the components of the Reynolds stress tensor $R$ by solving their governing transport equations.
    - Scale-Resolving Hybrid (SRH) Turbulence
      The Scale-Resolving Hybrid (SRH) turbulence model is a continuous hybrid RANS-LES model that combines the accurate prediction capabilities of LES with the low numerical cost of RANS. On fine meshes and when the time step is small, the SRH approach allows a RANS model to continuously switch to LES mode and resolve unsteady information of large-scale turbulent structures. In Simcenter STAR-CCM+, this hybrid method can be applied to K-Epsilon and K-Omega models.
    - Initialization and Inflow for RANS Turbulence Models
      The specification of realistic initial and inflow boundary values is important for good convergence and accurate simulation results.
    - Troubleshooting RANS Turbulence Solvers
      This section provides guidance for fixing problems with Reynolds-Averaged Navier-Stokes (RANS) turbulence solvers.
    - Modeling Turbulent Heat Flux
      The Temperature Flux Model replaces the Boussinesq approximation in the energy equation by an algebraic formulation for the turbulent heat flux. In Simcenter STAR-CCM+, this approach is available for the Standard K-Epsilon Low-Reynolds Number model.
    - Scaling Turbulent Viscosity
      The Turbulent Viscosity User Scaling model allows you to apply a custom scaling factor to the turbulent viscosity of K-Epsilon and K-Omega turbulence models.
    - Atmospheric Boundary Layers
      The Atmospheric Boundary Layer (ABL) is an important part of simulating wind and is used in modeling weather and wind-borne pollution, and in designing wind-farms.
  - Scale-Resolving Simulations
    In contrast to RANS models, scale-resolving simulations resolve the large scales of turbulence and model small-scale motions.
  - Wall Treatment
    Walls are a source of vorticity in most flow problems of practical importance. Therefore, an accurate prediction of flow and turbulence parameters across the wall boundary layer is essential.
- 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.

Deciding on a Spalart-Allmaras Model

To choose the appropriate model and wall treatment for your application take into account the following recommendations:

The Standard Spalart-Allmaras model, combined with the all- $y^{+}$ wall treatment, is recommended for most, if not all, applications.
The Standard Spalart-Allmaras model, combined with the low- $y^{+}$ wall treatment, could be used in situations where the mesh is known to be fine enough to resolve the viscous sublayer everywhere. The model is designed to give substantially the same results as the all- $y^{+}$ wall treatment.
The Detached Eddy Spalart-Allmaras model is only available with unsteady simulations, since detached eddy simulation is an inherently unsteady phenomenon.

The available Spalart-Allmaras models and wall treatments available in Simcenter STAR-CCM+ are:


Spalart-Allmaras Variant	Wall Treatment
Standard	low- $y^{+}$ , all- $y^{+}$
Detached Eddy	low- $y^{+}$ , all- $y^{+}$