Migrating from STAR-CD

This section lists details and limitations that guide you in migrating your STAR-CD files to Simcenter STAR-CCM+.

To convert a STAR-CD simulation to run under Simcenter STAR-CCM+, remember:

  • Simcenter STAR-CCM+ contains a Model Selection dialog where all physical and numerical models are chosen. The dialog contains an Auto-select recommended models checkbox which is ticked by default. Accept this setting unless you require special selections.
  • The high-Reynolds number formulation of the “standard” K-Epsilon turbulence model is commonly used in STAR-CD simulations. On the other hand, the Auto-select option is likely to lead to a Realizable Two-Layer K-Epsilon model. In most cases, the Realizable Two-Layer K-Epsilon model has acceptable, or even better results.
  • The default STAR-CD setting for initial k and ϵ values (as displayed on the STAR-CD GUI) is 0. When migrating your simulation, you are advised to use the Simcenter STAR-CCM+ (non-zero) defaults. Better still, use values that are in keeping with representative velocity, turbulence intensity and turbulent viscosity values in your problem.
  • There are important differences in the definition and required boundary conditions for inlet boundaries. Note in particular that, for mass flow inlets, the STAR-CD boundary conditions include velocity, density, static temperature and a “Flow Switch” setting. The corresponding Simcenter STAR-CCM+ conditions are mass flow rate, flow angle, pressure and total temperature.
  • For problems that involve porous media, STAR-CD uses settings for α and β. The corresponding settings in Simcenter STAR-CCM+ are porous inertial resistance Pi and porous viscous resistance Pv, respectively.
  • Follow Simcenter STAR-CCM+ guidelines on choosing suitable boundary conditions for your type of problem. For example, use pressure boundaries rather than outlets for compressible flows. As a result, change the definition of some of your existing STAR-CD boundary regions to more appropriate types.
  • There is no direct equivalent for the STAR-CD Maximum Residual Error Tolerance for use as an overall solution convergence criterion in steady-state problems. Similar criteria exist in Simcenter STAR-CCM+ and are available via the Monitors node, with each transport equation being solved. To form a composite stopping criterion:
    • Set up monitors for one or more of these equations.
    • Select the Create Stopping Criterion from Monitor option
    • Combine all monitor stopping criteria with the Maximum Steps criterion.
  • The default setting for convective flux discretization is a likely cause for significant differences in convergence rate between the two codes. STAR-CD uses first-order upwind differencing. Simcenter STAR-CCM+ uses a second-order differencing scheme which, in general, offers a better trade-off between accuracy and convergence rate.
  • To produce the equivalent of a STAR-CD surface (or hidden-line) velocity vector plot near wall boundaries, use the Cell Relative Velocity field function.
  • All of the Simcenter STAR-CCM+ post-processing plot types are defined in a suitable Scene. At the end of the simulation run certain plots, such as the Cell Relative Velocity, require that you click the Initialize button before the plot can be produced.
  • The Simcenter STAR-CCM+, option Thermodynamic Polynomial Data for specific heat is equivalent to the Polynomial option in STAR-CD when specifying physical properties for chemical reaction components. The polynomial curve fits for Cp (plus enthalpy and entropy) are read in from the Chemkin database. With these curve fits, values for Heat of Formation and Standard State Temperature are implicit in the curve fit for enthalpy. Simcenter STAR-CCM+ offers other options for specific heat: Polynomial in T (Cp is a piece-wise polynomial in temperature) or Constant (Cp is constant). If you use either option alone, specify the Heat of Formation and Standard State Temperature to determine the enthalpy in a simulation involving combustion.
  • The default setting in STAR-CD for combustion problems using the Eddy Break-up model is to include reaction product mass fractions in the calculation of the chemical reaction rate (option Use Products). Simcenter STAR-CCM+’s default setting for the rate calculation is ‘Do not use products’. This means that the chemical reaction simulation starts as soon as fuel and oxidizer come into contact. If you tick the ‘Use products’ option, set up an ignition model explicitly under the Ignitors node .