The following guidelines can help you make sure your CFD simulation is a success. Before contacting your technical support engineer, make sure you do the following:
There are two basic things that you should do before you start a simulation:
If there are mesh problems, you may have to re-mesh the problem.
In FLUENT, all physical dimensions are initially assumed to be in meters. You should scale the grid accordingly. Other quantities can also be scaled independent of other units used. FLUENT defaults to SI units.
For problems with conjugate heat transfer, when the conductivity ratio is very high, smaller values of the energy under-relaxation factor practically stall the convergence rate.
The node-based averaging scheme is known to be more accurate than the default cell-based scheme for unstructured meshes, most notably for triangular and tetrahedral meshes.
Residual plots can show when the residual values have reached the specified tolerance. After the simulation, note if your residuals have decreased by at least 3 orders of magnitude to at least 10 . For the pressure-based solver, the scaled energy residual must decrease to 10 . Also, the scaled species residual may need to decrease to 10 to achieve species balance.
You can also monitor lift, drag, or moment forces as well as pertinent variables or functions (e.g., surface integrals) at a boundary or any defined surface.
A converged solution is not necessarily a correct one. You should use the second-order upwind discretization scheme for final results.
After the simulation, note if overall property conservation has been achieved. In addition to monitoring residual and variable histories, you should also check for overall heat and mass balances. At a minimum, the net imbalance should be less than 1% of smallest flux through domain boundary.
You should ensure that the solution is grid-independent and use grid adaption to modify the grid or create additional meshes for the grid-independence study.
If flow features do not seem reasonable, you should reconsider your physical models and boundary conditions. Reconsider the choice of the boundaries location (or the domain). An inadequate choice of domain (especially the outlet boundary) can significantly impact solution accuracy.
You are encouraged to collaborate with your technical support engineer in order to develop a solution process that ensures good results for your specific application. This type of collaboration is a good investment of time for both yourself and the FLUENT support engineer.