- STAR-CCM+ contains a Model Selection dialog where all physical and numerical models used in the simulation are chosen. The dialog contains an Auto-select recommended models checkbox which is ticked by default. In general, you should accept this setting unless you have good reasons for making your own special selections.
- The turbulence model commonly used in STAR-CD simulations is the high-Reynolds number formulation of the "standard" K-Epsilon model. On the other hand, the Auto-select option above is likely to lead to a Realizable Two-Layer K-Epsilon setting. This should prove equally acceptable or even better for your problem.
- The default STAR-CD setting for initial k and
values (as displayed on the STAR-CD GUI) is 0. When migrating your simulation, you are advised to use STAR-CCM+'s own (non-zero) defaults. Better still, you should try to 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 STAR-CCM+ conditions are mass flow rate, flow angle, static pressure and total temperature.
- Try to follow STAR-CCM+ guidelines on choosing suitable boundary conditions for your type of problem (such as using pressure boundaries rather than flow-split outlets for compressible flows, or preferring velocity inlets to mass flow inlets for incompressible flows). As a result, it may be advisable to change the definition of some of your existing STAR-CD boundary regions to more appropriate types.
- There is no direct equivalent to STAR-CD's Maximum Residual Error Tolerance for use as an overall solution convergence criterion in steady-state problems. Similar criteria exist in STAR-CCM+ and are available via the Monitors node, in conjunction with each transport equation being solved. You will therefore need to set up monitors for one or more of these equations, selecting the Create Stopping Criterion from Monitor option to combine them with the Maximum Steps setting and thus form a composite stopping criterion.
- A likely cause for significant differences in convergence rate between the two codes is their default setting for convective flux discretization. The default scheme in STAR-CD is first-order upwind differencing. 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, select option from the velocity field's Function pop-up menu.
- All STAR-CCM+ post-processing plot types are defined in a suitable Scene and may be produced immediately following the end of the simulation run. Most of these plots may be reproduced later by opening the
.sim file and double-clicking the Scene definitions. However, certain plots (such as the one above) require that you first perform an initialization step (i.e. click the Initialize button) before the plot can be produced.
- When specifying physical properties for chemical reaction components in STAR-CCM+, option for specific heat is equivalent to the Polynomial option in STAR-CD; i.e. polynomial curve fits for Cp (plus enthalpy and entropy) are read in from the Chemkin database. With these curve fits, the user need not supply values for Heat of Formation and Standard State Temperature since they are implicit in the curve fit for enthalpy. STAR-CCM+ offers other options for specific heat: (Cp is represented by a piece-wise polynomial in temperature) or (Cp is constant). Either of these alone is not sufficient for determining enthalpy in a simulation involving combustion and therefore the user must provide Heat of Formation and Standard State Temperature as well.
- In solving combustion problems using the Eddy Break-up model, STAR-CD's default setting is to include reaction product mass fractions in the calculation of the chemical reaction rate (option Use Products). This necessitates definition of an ignition mechanism and relevant parameters in order to start off the reaction. 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 the `Use products' option is employed, the user should set up an ignition model explicitly under the Ignitors node .