A Quote from Anany, 2010, p. 15, Numerical Modelling of Combustion Processes at Elevated Pressures:
"On the other hand, chemically reactive flows are characterized by strong heat release accompanying the chemical reactions and, hence, by temperature-coupled density variations. Applying the time-averaging procedure to reacting flows introduces extra source terms to the transport equations due to these density variations. In order to avoid the density-related source terms, mass-averaging (Favre-averaging) techniques instead of time-averaging ones are implemented to overcome such inconvenience."
So for me in chemically reacting flows, the Favre average should be theoretically applied. There are many more sources from the 'Flamlet' community which state the usage of the Favre averaged equations. So, what does ANSYS Fluent use, when and under what conditions?
Best regards