Simple Outlet Question

m.nichols19 · June 14, 2010, 16:47

I am attempting to execute a simple test case using the icoFoam solver and have encountered a presumably easy problem that I cannot figure out. The mesh of the test case is a cylinder with a L-W ratio of 10:1. The inlet and outlet are on opposite faces of the cylinder. The inlet is given a relatively small initial velocity.

What should the boundary field conditions of the outlet be? I have attempted setting the velocity as zero and zeroGradient, and pressure as zeroGradient; however, those conditions return the following error:

Code:

Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.

The test case only runs when the boundary field condition of the outlet is given a velocity greater than zero.

best regards,
Matt

AlanR · June 15, 2010, 01:09

Matt,

The basic setup is to define the velocity value at the inlet (i.e. type fixedValue; value uniform (2 0 0)

and set velocity as zeroGradient at the outlet. For pressure, use zeroGradient at the inlet and a constant value of 'type fixedValue; value uniform 0;' at the outlet. For a good example, look in the pitzDaily tutorial (tutorials/incompressible/simpleFoam/pitzDaily). The airFoil2D and pitzDailyExptInlet tutorials have similar setups - the last one has an inlet velocity profile. I hope this helps,

Alan

m.nichols19 · June 15, 2010, 11:20

Hi Alan,

Thank you very much for you response. My issue was the pressure at the outlet.

I will also look at the tutorials that you mentioned.

best regards,
Matt

trex930 · June 25, 2010, 01:44

Hi Foamers,

Just a quick question.

When setting inlet velocity as fixed value. you have to type

type fixedValue;
value uniform (0 0 0);

What im curious about is the uniform part. If i put (2 0 0) does that mean 2m/s in x?

So if i have an angled inlet, should I use the components of the XY velocity?

Also one can choose to use inletflowRateVelcoityInlet correct? so when i type the flow rate. that does not have to be the components right?

What are the differences between those two?!

Thanks in advance!

Cheers,
Terence

June 14, 2010, 16:47	Simple Outlet Question	#1
m.nichols19 Member Join Date: Jun 2010 Posts: 31 Rep Power: 15	I am attempting to execute a simple test case using the icoFoam solver and have encountered a presumably easy problem that I cannot figure out. The mesh of the test case is a cylinder with a L-W ratio of 10:1. The inlet and outlet are on opposite faces of the cylinder. The inlet is given a relatively small initial velocity. What should the boundary field conditions of the outlet be? I have attempted setting the velocity as zero and zeroGradient, and pressure as zeroGradient; however, those conditions return the following error: Code: Continuity error cannot be removed by adjusting the outflow. Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow. The test case only runs when the boundary field condition of the outlet is given a velocity greater than zero. best regards, Matt

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June 15, 2010, 01:09		#2
AlanR Member Alan Russell Join Date: Aug 2009 Location: Boise, Idaho USA Posts: 61 Rep Power: 16	Matt, The basic setup is to define the velocity value at the inlet (i.e. type fixedValue; value uniform (2 0 0) and set velocity as zeroGradient at the outlet. For pressure, use zeroGradient at the inlet and a constant value of 'type fixedValue; value uniform 0;' at the outlet. For a good example, look in the pitzDaily tutorial (tutorials/incompressible/simpleFoam/pitzDaily). The airFoil2D and pitzDailyExptInlet tutorials have similar setups - the last one has an inlet velocity profile. I hope this helps, Alan

June 15, 2010, 11:20		#3
m.nichols19 Member Join Date: Jun 2010 Posts: 31 Rep Power: 15	Hi Alan, Thank you very much for you response. My issue was the pressure at the outlet. I will also look at the tutorials that you mentioned. best regards, Matt

June 25, 2010, 01:44		#4
trex930 Member Join Date: Jun 2010 Posts: 33 Rep Power: 15	Hi Foamers, Just a quick question. When setting inlet velocity as fixed value. you have to type type fixedValue; value uniform (0 0 0); What im curious about is the uniform part. If i put (2 0 0) does that mean 2m/s in x? So if i have an angled inlet, should I use the components of the XY velocity? Also one can choose to use inletflowRateVelcoityInlet correct? so when i type the flow rate. that does not have to be the components right? What are the differences between those two?! Thanks in advance! Cheers, Terence