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Inlet Velocity icm Outlet Velocity as boundery conditions doesn't work. Why?

Question asked by Luc Spruyt on Aug 12, 2013
Latest reply on Aug 21, 2013 by Jared Conway

Hello there,


Again I have a small issue with Flow Simulation.

It's probably due to the fact that I'm a little unexperienced.


Here's the question.


The job is to engineer a ducting system with the use of Fabric (e.g. FabricAir ) in order to fill a room with air going appr. 0.05 m/s.

The first try out is as shown on the picture.

The blue vertical tubes go outside the room.

The red ones represent the fabric channels that blow air inside.

We intend to create horizontal flowing air from the inlets to the outlets.

There is no temperature delta so convection is negligible.


We can asume that each clilinder produces air at a constant velocity of 0.05 m/s.

Therefore the boundery condition is " inlet velocity: 0.05 m/s" for all red cilinder surfaces.


When I put a "Static Pressure" boundery condition in the blue cilinders, I get realistic results.

But in real life the blue cilinders will have a pressure a little less then atmospheric because they are connected to the inlet channel of Fans.

They will suck air in.

So I thought, lets change the "Static Pressure" into "Outlet Velocity 0.05 m/s".

Because that the only parameter we have. The fabric is designed for this speed.

That combination didn't work.


So the question is:


Why can't we have a Outlet Velocity in combination with Inlet Velocity for a study.



When I change it back to Static Pressure of lets say 1 bar (atm = 1.03 ) so 3000 Pa under pressure then there is no flow.


What am I doing wrong.


ps sorry for the poor englisch writing here and there.


Thanks again.

Luc Spruyt