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Outlet with mass flow specified: temperatures diverge

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Old   April 25, 2016, 08:57
Default Outlet with mass flow specified: temperatures diverge
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Sarah Leenknegt
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Dear,

I am trying to run a case with an air curtain at the entrance of a large building, including an outdoor "box" with athmospheric boundaries.
I keep seeing the temperatures at the outlet boundary diverge to unrealistic high values. The meshcheck is successfull, and further refinements have also been made, so I assume the problem is my boundary condition at the outlet. The high temperatures occur at the boundary cells at the outlet area. Already after 20 iterations, the problem starts.

I can post pictures of the geometry with mesh, when required.

The case is running with buoyantboussinesqsimplefoam and kwSST, GAMG solver for p_rgh.

My outlet BDC:
- p = fixedfluxpressure
- p_rgh = fixedfluxpressure
- T = 12 C (in case of backflow)
- v = x 0; y 1.8; z 0 m/s
- omega = zero gradient
- k = zero gradient
- kappa, alpha, nu = calculated

Important is that I can define the mass flow at the outlet, otherwise the supplied hot air from the air curtain would just flow through the door to outside.

I would appreciate any feedback on potential errors! I have been playing around with different BDC's, but have not found a solution. Or should I look again at my mesh or something else going on with the solver?


In case relevant:

My inlet BDC:
- p = fixedfluxpressure
- p_rgh = fixedfluxpressure
- T = 32 C
- v = x 0; y 0; z -6 m/s
- omega = turb mix length 0.1 m
- k = turb intensity 5 %
- kappa, alpha, nu = calculated

My athmospheric BDC:
- p = fixedfluxpressure
- p_rgh = totalpressure
- T = -4 C
- v = pressureinletoutletvelocity
- omega = turb mix length 0.1 m
- k = turb intensity 5 %
- kappa, alpha, nu = calculated

Thanks a lot!

Sarah
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Old   May 10, 2016, 05:38
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Sarah Leenknegt
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In case it can help someone else:

The solution was to set the thermal boundary condition at the outlet to zero gradient.
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buoyanboussinesqsimple, divergence of temperature, outlet bc

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