KNOWN ISSUE: Use of Residual Material model with fuel vapour (Class 3 Error)
When running cases that combine premixed or partially premixed models for combustion with the Residual Material Model, the CFX-Solver can produce unphysical temperatures and may even crash.
The internal CFX model for mixing fuel material with residual material in a premixed or partially premixed combustion calculation assumes some partial relaxation to chemical equilibrium, which may lead to the dissociation of CO2 within the residual material. In some circumstances, e.g. fuel evaporation from particles, this can lead to unphysical results often depicted by very low gas temperatures. It is more appropriate in the majority of cases to have inert mixing of the fuel and residual materials.
No workaround is currently available.
ANSYS CFX Release 12.1. A custom executable for ANSYS CFX Release 12.0 is available on request.