# Simple Model Problem (Reversed Flow)

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 April 26, 2012, 00:45 Simple Model Problem (Reversed Flow) #1 New Member   Dominic Ow Join Date: Apr 2012 Posts: 9 Rep Power: 14 Dear all, I am trying to obtain the velocity streamline for a ventilation system and I have generated a simple 5m by 5m room with a protruded squared surface that represents the air-conditioning system. The general idea is to observe the streamline pattern as it fills the room and exits through the window. However, the flow profile doesn't behave as expected as it 'creeps' through the walls rather than filling the empty room spaces. Please advice! Uploaded with ImageShack.us

 April 26, 2012, 01:16 #2 New Member   mj Join Date: Apr 2010 Posts: 5 Rep Power: 16 I think your simulation didn't reach convergence (see legend of the left top, do u think the velocity in your problem will be higher than 1e2m/s)

 April 26, 2012, 01:24 #3 New Member   Dominic Ow Join Date: Apr 2012 Posts: 9 Rep Power: 14 Many thanks for the swift reply doctor evil. No, of course it wouldn't be that high. (that said, I don't know how it got that value, my inlet velocity was set to 5 m/s) Also, How do I ensure convergence has occured?

 April 26, 2012, 04:37 #4 Member   Daniel Tanner Join Date: Apr 2009 Posts: 54 Rep Power: 17 Are you sure that the size of your room is what you think it is? If it is a cm to meter difference this might explain why the velocities are high. Check the domain size in the scale dialogue.

April 26, 2012, 05:01
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Join Date: Nov 2011
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Moreover what boundary condition do you use for outlet? What turbulence model do you use? Is it isothermal case? Also some information about mesh would help us (Mesh -> Info -> Quality, Mesh -> Info -> Size).

Quote:
 Also, How do I ensure convergence has occured?
At least values of residuals for continuity and velocity should be below 10^-3. For energy it is 10^-6. However more important is to monitor quantities, which have physical meaning. For example, for your problem it could be mass flow of air on inlet and outlet. Difference between them shouldn't be higher then several percents.

Last edited by Sixkillers; April 26, 2012 at 05:17.

 Tags backflow, fluent, streamline, velocity, ventilation

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