Inlet and Outlet BC

Claudio2010 · September 8, 2009, 18:09

Hello,

I am new to Ansys and CFX and I read in a tutorial that an Inlet BC only allows fluid to enter to the domain and Outlet only to exit. Is this so?

Can a fluid actually exit through an Inlet type BC?

I ask this because at one of the boundaries I want to impose a sinusoidal velocity, so fluid will enter and exit the domain through that same boundary.

Or would I have to use a open boundary?

Thanks!

ghorrocks · September 9, 2009, 00:22

Yes, inlets and outlets only allow flow in one direction. If you want to allow flow in both directions you need an opening.

NickFL · September 9, 2009, 07:18

I have done similar problems. For instance if you have flow in a pipe, you can apply a sinusoidal velocity at one end (specified as an inlet) and a opening at the other end. This configuration will allow flow to enter the opening end the domain when the "inlet" has a negative velocity.

A clarification on what Glenn said: yes for inlet boundary condition the flow is only allowed to have one flow direction across the area at each time step. However between time steps the flow can change directions. For instance if at time 1 the flow is entering the domain at an inlet, then at time 2 the flow can leave the same boundary at an inlet. However at time 1 all points on the inlet need to have flow entering the domain (or be zero) and at time 2 all points on the inlet need to have flow leaving the domain (or be zero). Hopefully that isn't too confusing.

September 8, 2009, 18:09	Inlet and Outlet BC	#1
Claudio2010 New Member Claudio Join Date: Jul 2009 Posts: 9 Rep Power: 16	Hello, I am new to Ansys and CFX and I read in a tutorial that an Inlet BC only allows fluid to enter to the domain and Outlet only to exit. Is this so? Can a fluid actually exit through an Inlet type BC? I ask this because at one of the boundaries I want to impose a sinusoidal velocity, so fluid will enter and exit the domain through that same boundary. Or would I have to use a open boundary? Thanks!

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September 9, 2009, 00:22		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Yes, inlets and outlets only allow flow in one direction. If you want to allow flow in both directions you need an opening.

September 9, 2009, 07:18		#3
NickFL Senior Member Join Date: Jun 2009 Location: Technische Universität Chemnitz Posts: 107 Rep Power: 16	I have done similar problems. For instance if you have flow in a pipe, you can apply a sinusoidal velocity at one end (specified as an inlet) and a opening at the other end. This configuration will allow flow to enter the opening end the domain when the "inlet" has a negative velocity. A clarification on what Glenn said: yes for inlet boundary condition the flow is only allowed to have one flow direction across the area at each time step. However between time steps the flow can change directions. For instance if at time 1 the flow is entering the domain at an inlet, then at time 2 the flow can leave the same boundary at an inlet. However at time 1 all points on the inlet need to have flow entering the domain (or be zero) and at time 2 all points on the inlet need to have flow leaving the domain (or be zero). Hopefully that isn't too confusing.