Dear users,

I have a doubt. While specifying the 'Pressure boudary' for scalar, is it mandatary to specify the mass fraction in case of multicomponet problems as in most of the cases the outlet concentration is unknown? kindly let us know if there is any way of avoiding the concentration input with pressure boundary condition.

thank you, pathak

The mass fractions only become interesting when you got inflow conditions on your pressure boundary. It is pretty much the same as with temperature at the pressure bc. Nevertheless, you should have an idea of the scalar concentrations at the outlet as a result of the inlet conditions anyway.

thats true. but in transient cases the outlet concentration is varying with time whose values are difficult to predict beforehand. So we can not give a constant value for all the time.

Good point. You have a number of options then.

Move your pressure boundary downstream in order to prevent inflow.

If it is just a smallish recirculation in your pressure bc, have a look if the recirculated flow is transported upstream. If not it might not have any impact on the regions of interest.

Just use average values of concentrations or use an inert gas in case of combustion.

What is it you are modelling?