# Reversed flow at pressure outlet

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 November 29, 2006, 12:48 Reversed flow at pressure outlet #1 Seeker Phil Guest   Posts: n/a Hey all... I was wondering if some of the experts here had any idea about the physical implications of reversed flow at pressure outlets. I am running a problem with an oscillating flow and during half the cycle my flow is reversed at the pressure outlet. I have specified a guage pressure = 0 Pa at this boundary. However, due to this backflow the pressure after iterating is about -1.5 Pa. The documentation does not do a great job of explaining what happens to the flow when a reversed flow at the pressure outlet occurs. So I would appreciate any ideas and thoughts on this. Also, any tips to reduce/avoid this backflow would be appreciated. Thanks, Phil

 November 30, 2006, 21:55 Re: Reversed flow at pressure outlet #2 Ahmed Guest   Posts: n/a Extend your domain at this outlet

 December 1, 2006, 13:41 Re: Reversed flow at pressure outlet #3 Seeker Phil Guest   Posts: n/a Thanks for the suggestion. I will try that out! Phil

 December 19, 2006, 22:06 Re: Reversed flow at pressure outlet #4 chiu Guest   Posts: n/a Phil, please let me know how it goes as i am dealing with a similar flow profile - sinusoidal velocity inlet. but in my case, reversed flow does exist physically within a computed time cycle. cheers chiu

 December 28, 2009, 21:17 Reversed flow ... #5 New Member   Mrt Join Date: Mar 2009 Posts: 21 Rep Power: 17 Is there any other way beside extending the domain to further away? Actually, I have this message ''reversed flow on pressure outlets...'' but there is now problem seems about converging of the Model. Is reversed flow... really a problem that should be fixed? Thanks, Murat

 December 28, 2009, 23:00 #6 New Member   Wah Keng Sern Join Date: Oct 2009 Posts: 6 Rep Power: 16 Hi seeker phil, are you simulating a column or other things ?? Try to set the outlet pressure in vaccum and check whether can solved the reversed problem.

December 30, 2009, 18:01
#7
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Quote:
 Originally Posted by Seeker Phil ;137262 Hey all... I was wondering if some of the experts here had any idea about the physical implications of reversed flow at pressure outlets. I am running a problem with an oscillating flow and during half the cycle my flow is reversed at the pressure outlet. I have specified a guage pressure = 0 Pa at this boundary. However, due to this backflow the pressure after iterating is about -1.5 Pa. The documentation does not do a great job of explaining what happens to the flow when a reversed flow at the pressure outlet occurs. So I would appreciate any ideas and thoughts on this. Also, any tips to reduce/avoid this backflow would be appreciated. Thanks, Phil
Are you saying it is unphysical or is the domain too short? If it's causing problems with conversion you might try setting it to an opening instead, which doesn't create artificial walls when flow is reverse.

 January 1, 2010, 22:16 #8 Senior Member     teguh hady Join Date: Aug 2009 Location: Saga, Japan Posts: 222 Rep Power: 17 "Are you saying it is unphysical or is the domain too short? If it's causing problems with conversion you might try setting it to an opening instead, which doesn't create artificial walls when flow is reverse." Hei kingjewel1 I've the same problem. I have back flow problem. I'm interested in looking further on your advice. By the way, I cannot understand in reading your advice well. i'm sorry if my English is poor!!! thanks teguhtf __________________ Now Or Never!!!

 January 2, 2010, 03:52 #9 Senior Member   Join Date: Jul 2009 Posts: 260 Rep Power: 17 By making the Boundary an Opening the fluid is free to go into the domain as well as out. You can still give it the same properties. But in general back flow into a domain is caused by the domain not extending far enough downstream of the phenomenon

January 2, 2010, 05:21
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What is the name of that opening?? outflow, or what?? well, my project is comparing simulation and experiment about water turbine in 2D. My supervisor asks me to get error below than 10% (difference simulation and experiment). I compare torque. It's difficult for me to get that. my error is high (about 40%). I think there is error in my boundary specification (especially outlet).to reduce back flow i tune gauge pressure and kind of turbulence in that boundary. well, it works but that's not significant. Do you have any advice??

thank you
teguh
PS. I attach my turbulence kinetic energy & summary report.
Attached Images
 TURBULENCE ENEGY CONTOUR.JPG (93.9 KB, 78 views)
Attached Files
 SUMMARY REPORT.txt (95.8 KB, 39 views)
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