# Boundary condition for Natural convection

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 August 21, 2013, 07:30 Boundary condition for Natural convection #1 New Member   rabbi tonmoy Join Date: Aug 2013 Location: dhaka Posts: 1 Rep Power: 0 My project is laminar free convection over a vertical plate. my domain is 100x100 cm and body size 2x6 cm may be I face problem for setting boundary condition. I set boundary condition as- 1.Inlet at the bottom (pressure inlet)gauge pressure 0 pa, and intial pressure 0.inlet temp 275k 2.outlet at the top (pressure outlet) gauge pressure o.back flow temp 275k. 3. object (wall). convection-Heat transfer coefficient-25, body temp 325k 4.symmetry(right and left portion) of domain operating condition 101325 pa, gravity on,operating density on (1.225) I face problem in reversed flow. Is there something I am missing in setting up the pressure boundary conditions? please give a solution for overcoming this problem

 August 21, 2013, 09:37 #2 Super Moderator     Alex Join Date: Jun 2012 Location: Germany Posts: 3,033 Rep Power: 43 The reversed flow WARNING only indicates that at some faces, the fluid flows in the opposite direction (out of the domain at the inlet or into the domain at the outlet). If you think about the flow field that is prodced by a heat source especially if the flow is turbulent, a backflow is very likely. You could try to initialize the flow field with a small velocity pointing in the right direction. But if the reversed flow warning appears again this is most likely the correct physical behavior of the flow. Edit: The assumption of laminar flow might be wrong. How did you get to this conclusion? Last edited by flotus1; August 25, 2013 at 08:59.

 August 25, 2013, 08:58 #3 New Member   JAY Join Date: Jul 2013 Posts: 10 Rep Power: 11 I have some problem with my boundary condition that how i utilize the neumann condition(∂φ/∂x = 0) at outlet. Can i select pressure outlet at outlet? my inlet condition is : flat velocity profile =40m/s Re=1.916*10^5 turbulent intensity=4.5% And Inlet height of duct=5mm I select velocity inlet at inlet because my flow is incompresible. And axis boundary condition applied along the centerline. and no slip condition at wall. pls help me.

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