Passive Scalar

Andy R

Folks, I have a combustion problem with multiple gas injectors. The analysis looks good so far but a question has come up. Can I show how much of the unburnt fuel at a given point has come from each injector.

I believe that the way to do this is to use the UDS (user defined scalar) and have set those up and the results seem broadly plausible. But....

I seem to be getting small but finite concentrations of all my passive scalars well upstream of the injection points in the oxidizer air stream. The flow is super sonic at around Mach 2 so certainly these scalars cant be convecting upstream.

Am I just seeing a start up transient to the solution (I am running this SS)? Or am I missing something in my setup?

I have used the default values for UDS diffusivity relative to my "real" scalars. That value defaults to 1.

I am assuming that if I get this set up correctly a finite concentration of a passive scalar will indicate that any unburt fuel in a cell can be traced back to one or more injection locations based on the relative concentrations of the N UDScalars I have defined.

Ultimately I would like to track product production as well but I think I would have to add N more UDScalars and a UDF to destroy the correct amount of fuel tracking scalar and create the correct amount of product tracking scalar.

Any thoughts? Thanks - Andy