# Opening Boundary Condition

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 August 21, 2010, 09:34 Opening Boundary Condition #1 New Member   Rosa Esposito Join Date: May 2009 Posts: 5 Rep Power: 8 I am trying to model an opning Boundary Condition. The flow regime is Subsonic, but I am unsure about the Mass and MOmentum. I don't know which condition would be better, the opening pressure and direction or the entrainment. I read all the post about this topic and also the guide of cfx but the difference between these two conditions is still not clear to me. Can anyone explain to me the difference (with some picture), or at least give me some paper or reference ? I can give my private mail. Any help would be appreciated.

 August 21, 2010, 09:45 #2 Member   Ciro Cannavacciuolo Join Date: Mar 2009 Posts: 35 Rep Power: 8 hi, try to explain me better your simulation. Your name sounds italian, we can avoid to talk in english if I'm right. My private email is cannavacciuolociro@gmail.com Bye

 August 22, 2010, 08:18 #3 New Member   Rosa Esposito Join Date: May 2009 Posts: 5 Rep Power: 8 Ciao! I am simulating the flow of an annular aspiration duct (d=3 mm). I put this aspiration duct in a big room, I suppose, somthing like 200 mm. But if I give different conditins to the opening, (opening pressure r entrainment) I got VERY different result. The thing is, I know that maybe I should reproduce a bigger domain, but i am not sure that I have the computational resources to do that ( I already have something like 4000000 cells and believe me). So my question is: Why the entrainment condition affects sooo much my result? HAs anyone already some experience with this matter? Is entrainment indeed the best choice for this case? I can not put the case online, but of course I can mail to you.

 August 22, 2010, 13:38 #4 Member   Ciro Cannavacciuolo Join Date: Mar 2009 Posts: 35 Rep Power: 8 I'm not sure I've understood your simulation and in particoular I didn't understand where you have to set the opening condition. Maybe you can show me a picture o something to explain me better the situation. I simulated a semi submerged propeller with an opening condition at the end of my domain. I've not the file with me, know, but I can check as soon as possible the BC I used. About it I can say that the results where very good. So, let me know better your domain and the distribution of your BC. I'll help you , if I can. Another question: which is the goal of your simulation?

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