wall condition for extended outlet

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 April 6, 2010, 10:52 wall condition for extended outlet #1 New Member   Join Date: Jun 2009 Posts: 20 Rep Power: 10 Sponsored Links Hi everyone! In my calculation, I extended the outlet to prevent inflow as recommend in the CFX documentation. I just want to ask if it's appropriate to assign the wall of the additional region as free slip (no slip in the main domain) so as not to further retard the flow. Is this correct? thanks a lot guys! kuh

 April 6, 2010, 12:55 #2 Member   Dmitry Volkind Join Date: Jan 2010 Location: Ekaterinburg, Russia Posts: 61 Rep Power: 9 Depends on what You are modelling. Why don't You want to retard the flow?

 April 6, 2010, 13:19 #3 New Member   Join Date: Jun 2009 Posts: 20 Rep Power: 10 Hi! Thank you for your reply. I'm simulating 2 phase flow and there is some recirculation near the outlet. My outlet condition is based on experimental data and I'm afraid that further extending it would have some inaccuracy.

 April 6, 2010, 13:35 #4 Member   Dmitry Volkind Join Date: Jan 2010 Location: Ekaterinburg, Russia Posts: 61 Rep Power: 9 What are Your BCs?

 April 6, 2010, 13:37 #5 New Member   Join Date: Jun 2009 Posts: 20 Rep Power: 10 My BCs are velocity in and pressure out. Tnx!

 April 6, 2010, 13:58 #6 Member   Dmitry Volkind Join Date: Jan 2010 Location: Ekaterinburg, Russia Posts: 61 Rep Power: 9 Then moving outlet further away most likely won't affect accuracy. With inlet speed specified You will get a higher inlet pressure then You would expect without moving the boundary. Thus, absolute pressure values might slightly change, but basically pressure differences are important. So, if the absolute pressure level does not have much effect for Your problem and extending the domain won't introduce new geometry features then I think it's OK to move the boundary. By the way, wall shear stress at non-sleep wall is not the only cause of pressure loss, so there's no guarantee that You won't get any pressure drop in free-slip region.

 April 6, 2010, 14:02 #7 New Member   Join Date: Jun 2009 Posts: 20 Rep Power: 10 Thank you very much for the input! I'll run few more simulations and check if there's effect. Thanks again!

 April 6, 2010, 18:41 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,724 Rep Power: 106 The best way to look at it is you want to model what the experimentalists measured. If they had a long runner downstream of the test section, then model that. If they dumped it into a big tank then model that.

 April 8, 2010, 10:30 #9 New Member   Join Date: Jun 2009 Posts: 20 Rep Power: 10 Thanks again Sir Glenn! I'll take note of that.

 Tags outlet wall, slip

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