Flow recirculation - UDF boundary conditions

vinerm · May 21, 2020, 16:30

The conditions you are using are correct. In that case, you should get maximum temperature at the top. How does the temperature profile look?

cfdEng_ · May 26, 2020, 17:49

If I impose Symmetry BC to the sidewalls (as discussed), I can't achieve a converged solution. I get a "hot core" in the middle of my duct and colder air elsewhere.

Nevertheless, by setting no-slip sidewalls, the simulation converges and I get a reasonable temperature profile.

The mesh I used works perfectly with a regular Velocity Inlet but it seems problematic for a Periodic Inlet. Do you think such an issue can be due to the quality of my mesh or is there something else I should look at?

Thank you very much in advance.

vinerm · May 27, 2020, 04:12

Symmetry condition is equivalent to free-slip for momentum and adiabatic for thermal. So, if you want to model infinite domain across width, then it should be symmetry. If there are walls, then no-slip is more accurate. Even if you change it to no-slip wall, default for thermal boundary is still adiabatic and the changes in the thermal profile are only because of convection, which changed because of boundary condition being changed from free-slip (symmetry) to no-slip.

Whether to use no-slip or symmetry depends on whether you have infinite or finite domain across width.

May 21, 2020, 16:30	Thermal Condition	#21
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	The conditions you are using are correct. In that case, you should get maximum temperature at the top. How does the temperature profile look? cfdEng_ likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 27, 2020, 04:12	Symmetry	#23
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	Symmetry condition is equivalent to free-slip for momentum and adiabatic for thermal. So, if you want to model infinite domain across width, then it should be symmetry. If there are walls, then no-slip is more accurate. Even if you change it to no-slip wall, default for thermal boundary is still adiabatic and the changes in the thermal profile are only because of convection, which changed because of boundary condition being changed from free-slip (symmetry) to no-slip. Whether to use no-slip or symmetry depends on whether you have infinite or finite domain across width. cfdEng_ likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

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May 26, 2020, 17:49		#22
cfdEng_ New Member Join Date: Apr 2020 Posts: 26 Rep Power: 6	If I impose Symmetry BC to the sidewalls (as discussed), I can't achieve a converged solution. I get a "hot core" in the middle of my duct and colder air elsewhere. Nevertheless, by setting no-slip sidewalls, the simulation converges and I get a reasonable temperature profile. The mesh I used works perfectly with a regular Velocity Inlet but it seems problematic for a Periodic Inlet. Do you think such an issue can be due to the quality of my mesh or is there something else I should look at? Thank you very much in advance.