Exhaust's air flow in wrong direction

Sandy7 · February 8, 2017, 19:46

Hello Star CCM + users,

The air flow at the house exhaust is going inward, however, exhaust type is pressure outlet. Secondly, velocity value at outlet is higher as compared with inlet value. The screenshot is attached. Any suggestions? what could be wrong?
In back-flow specifications
Direction: Boundary-Normal(this option doesn't specify the direction)
Pressure - Environmental

Thanks,
Sandy

me3840 · February 10, 2017, 09:55

A pressure boundary condition doesn't set the flow direction, it's dependent on the physics of the problem. If there is reversed flow then the pressure of the system must be lower than the outlet pressure.

The velocity at the outlet being higher from your picture is probably fine since there are multiple smaller outlets, so mass is probably still conserved.

Sandy7 · February 15, 2017, 13:19

Thanks me3840!

You are right, I figured out that the volume fraction of air inside the building wasn't defined in initial conditions that is why there was reverse flow!

Sandy

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February 10, 2017, 09:55		#2
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	A pressure boundary condition doesn't set the flow direction, it's dependent on the physics of the problem. If there is reversed flow then the pressure of the system must be lower than the outlet pressure. The velocity at the outlet being higher from your picture is probably fine since there are multiple smaller outlets, so mass is probably still conserved.

February 15, 2017, 13:19		#3
Sandy7 New Member Sandy Join Date: Dec 2016 Posts: 10 Rep Power: 9	Thanks me3840! You are right, I figured out that the volume fraction of air inside the building wasn't defined in initial conditions that is why there was reverse flow! Sandy