# Jet fan and Tunnel simulation

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 April 6, 2009, 12:30 Jet fan and Tunnel simulation #1 New Member   Join Date: Mar 2009 Posts: 8 Rep Power: 9 Hello, I am simulating a jet fan in a tunnel. The fan is set in a simple way: a cylinder with one end as entrance of the jet fan and another end as exit of the jet fan. A tunnel air domain was cut by this fan cylinder and set the entrance of jet fan as an outlet and the exit of the jet fan as an inlet of the domain. Two ends of the tunnel were set as openings with static pressure zero Pa. The jet fan has 26m/s velocity with area 1.16m^2 The tunnel section is 45m^2 and 300m length. The simulation went well and converged well, but the result looks not realistic. The tunnel average velocity is 20m/s! It needs a huge power to drive this flow. The jet fan obviously has a small portion of such a power. Where it was wrong...? Turbulence model used is k-e with 5% intensity Thanks for any help Ahlo

 April 6, 2009, 16:44 #2 Senior Member   Michael P. Owen Join Date: Mar 2009 Posts: 196 Rep Power: 9 I'm not sure I understand the problem set up, but it sounds like you may have a poorly defined problem that may admit multiple solutions. You say that you have 0 static pressure openings defined at both ends of the tunnel? The wind can blow through the tunnel at any speed in a case like this.

April 9, 2009, 10:18
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Quote:
 Originally Posted by michael_owen I'm not sure I understand the problem set up, but it sounds like you may have a poorly defined problem that may admit multiple solutions. You say that you have 0 static pressure openings defined at both ends of the tunnel? The wind can blow through the tunnel at any speed in a case like this.

Thank you, Michael

It is possible the BC were not well defined and it risks in having multiple solutions.
I assumed there is friction induced pressure drop along the tunnel, and this will somehow limit the air speed although with end of the tunnel have Pstatic=0. I added some back pressure at exit end of the tunnel, it improved, but velocity still looks high.

Any Suggestion to set better BC?

 April 15, 2009, 07:02 #4 New Member   Tassi Join Date: Mar 2009 Location: Mumbai, India Posts: 11 Rep Power: 9 Hi Didn't understand you description that well. I suggest you give outlet BC as velocity or mass flow and inlet as Static Pressure.

 April 16, 2009, 02:55 #5 Member   Pratik Mehta Join Date: Mar 2009 Posts: 32 Rep Power: 9 Hi, I would suggest that you attach a .jpeg of your case describing your domain in that image . To me also it not clear how your problem is setup and the way you are defining your boundary conditions Best regards Pratik

 June 10, 2010, 06:12 jet fan boundary condition #6 New Member   Join Date: May 2010 Posts: 4 Rep Power: 8 hi there i was wondering if i can find help with my issue. i ve been using fluent in simulation of ventilation in rooms. my main task is to simulate a garage ventilation model using gambit and fluent. concerning the jet fans, i wonder wht kind of boundry condition shall i insert in the inlet and outlet. shall i treat the inlet as PRESSURE OUTLET, and outlet of the fan as VELOCITY INLET? or there is another boundary identification concerning the fan? thats for the normal ventilation, and soon i ll send a question concerning the smoke extraction. i hope i ll find help with that. thank u in advance

 June 10, 2010, 08:04 #7 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 Doesn't Fluent have a fan boundary condition. Not sure. You are asking the wrong forum, this is the CFX forum.

 March 7, 2012, 11:25 #8 New Member   christopher Join Date: Feb 2012 Posts: 1 Rep Power: 0 Hi, I want to make a jet fan simulation in a tunnel too, but I'm new in openFoam and a I really need some help. What solver do you use to get the simulation? How do you set the boundary conditions? Can you send me some tutorial or information about jet fan simulation ? or can you send me your work? I'll be very grateful!

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