Hello,

I am running scalar mixing of air and fuel inside a small tube. When I start the solver I get a message like:

Unless the flow is supersonic the outlet boundary is not well posed.

The flow is not supersonic at the outlet. I get M close to 0.7 near one of the inlets, but the outlet diametre is much larger.

Does anyone know what this could mean?

thanks,

Thomas

An outlet boundary can be used for compressible flows only under limited circumstances. There's a section in chapter 6 of the user guide which explains these.

thanks

Hi, generally outlet boundaries are not used for compressible flows. This has been the rule for all solvers. Try using a different boundary condition, instead of 'outlet' boundary.