# mixing flow

 Register Blogs Members List Search Today's Posts Mark Forums Read

 May 11, 2009, 03:44 mixing flow #1 New Member   Join Date: May 2009 Posts: 6 Rep Power: 10 The model is basically a large diameter duct with a thin injection tube on the side (T-shape with 2 inlets and 1 outlet). After running the sym, the air speed at the interior goes to the order of 10^16 m/s! During the first iterations, the speed starts going crazy at the inlet of the small tube. Afterwards the whole system has this unrealistic velocity gradients. The inlets speeds are supposed to be around 15 m/s and I`ve tried for boundery conditions the "velocity inlet" and "pressure inlet". I`ve also tried refining the mesh and using various turbulance models. I was hoping to get something close to laminar flow (15m/s) at the center of the tubes. I`d appreciate it if you have any idea of what`s causing this problem .

 May 11, 2009, 10:40 #2 Member   zhao peng Join Date: Mar 2009 Posts: 41 Rep Power: 10 How did you set the outlet boundary?

 May 11, 2009, 18:37 #3 New Member   Join Date: May 2009 Posts: 6 Rep Power: 10 zhao peng, thank you for your reply. I set the outlet boundary as a pressure outlet, with stagnation pressure of 1atm

 May 12, 2009, 01:10 #4 Member   zhao peng Join Date: Mar 2009 Posts: 41 Rep Power: 10 what is the pressure differential between major inlet and outlet?and is the air compressible?

 May 12, 2009, 01:59 #5 New Member   Join Date: May 2009 Posts: 6 Rep Power: 10 Between the inlet and outlet of the large pipe is 135 Pa and the gauge total pressure of the injection inlet is 540 Pa. This way I got a initialization speed of 15 m/s in the large duct and 30m/s in injection tube. Thank you again.

 May 12, 2009, 19:29 #6 New Member   Join Date: May 2009 Posts: 6 Rep Power: 10 I forgot to mention I`m treating it as incompressible beacuse of the low speed of the airflow.

 May 12, 2009, 21:55 #7 New Member   Martin Gariepy Join Date: Mar 2009 Location: Laval Posts: 13 Rep Power: 10 Dear kikimon There is something wrong with your boundary condition and/or operating pressure. The veloity you obtain let me think about a pressure differential between the inlet and oulet of around 100000Pa. What might happen is this:if you set your operatiing pressure at, let say 101325, then you should set all the pressure as gauge pressure, then your outlet pressure will be zero and the inlet pressure will be 0+delta_P where delta_p his suppose to be the pressure differential that you want beetween the inlet and outlet. Hope it's help Martin

 May 13, 2009, 02:31 #8 New Member   Join Date: May 2009 Posts: 6 Rep Power: 10 Thank you Martin for your response. I did set the outlet pressure as 0Pa and took into consideration the gauge term. Anyway, the problem is solved, it was the solver equations I was using. I ran 40 iterations with simple-standard and 100 more with coupled-second order and finally got it to converge with reasonalbe quatities. It might be something I should`ve known, but this was the first all-by-myself fluelnt sym, thank you both for your answers.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post kevin FLUENT 8 August 11, 2015 13:00 goodegg Main CFD Forum 12 January 22, 2013 12:47 srinivas FLUENT 0 November 8, 2006 05:52 diaw Main CFD Forum 104 February 16, 2006 06:44 Wen Long Main CFD Forum 3 September 24, 2002 08:47

All times are GMT -4. The time now is 22:05.