Discussion Forum

Hello Everyone,

I currently have a pipe with water flowing through it. I have verified/solved this model to as accurately as I can. I then have insert a small nozzel at one end of the pipe (1/20th the length of the pipe). This is injecting fluid with Exactly The Same Properties, but the Flow Rate will be different.

Using Pousille I have calculated for my flow rates an expected inlet velocity for the pipe and the nozzle.
I then set my inlet BC's to "Mass Flow Rate" using the desired inlet's. It solves wonderfully, my Delta_P is what I expected. My exit flow rate is the combination of both mass flow rates, and *My inlet velocity on the pipe and nozzle are what I calculated*

Question - However, when entering any other inlet conditions I'm unable to solve. If I enter my BC's as "Velocity" it will not solve. The same goes for setting laminar inflow "Average velocity" and "Flow Rate". Though I suspect the laminar inflow case is because Comsol is having trouble with two assumed full developed flows intersecting, thus no longer being fully developed.

The Reynolds number is around ~ 400. The flows should exhibit no turbulence, though I know their is natural turbulence when flows will mix, is this causing the problem?

Thanks for any tips understanding the various inlet conditions. I assume if I can get it working with the correct physics for mass flow rate, I should be able to calculate velocity and pressures and have it solve as well.