Unphysical particle and gas temperature values are encountered in particle tracking simulations in the CFX 10.0 Solver.
This problem may occur in the following cases:
- particle convective heat transfer only
- when using the particle evaporation model
The problem is more likely to occur if the particle mass loading is high. Both particle and gas temperatures may be unphysical. Unphysical temperatures are caused by overshoots in the particle source values. This situation can be dealt with in a number of ways, depending on the models used.
If the simulation does not include particle evaporation, it may be sufficient to set a suitable particle under-relaxation factor for the particle energy source. A value of 0.1 is a suitable starting point. Setting the same under-relaxation factor for the particle momentum source is recommended.
For evaporation cases it may also be necessary to under-relax the particle mass source and disable particle enthalpy source linearisation. This is because the particle mass source is not linearised and having only one source linearised can cause instability. Setting the same under-relaxation factor for enthalpy, mass and again momentum is recommended.
The following expert parameter setting disables particle enthalpy source linearisation:
'pt linear src coef multiplier = 0.0'
In cases where the particle sources are under-relaxed, more iterations may be required to achieve a converged solution.