# Thermal Boundary layer

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 March 21, 2012, 22:01 Thermal Boundary layer #1 New Member   Leandro Join Date: Mar 2012 Posts: 8 Rep Power: 7 Hello guys! I have been working in a simulation that consists in a air flow over a heated rotating cylinder. I' m trying to visualize the thermal boundary layer. I have used the Coutours- Static temperature, but the results doesn't look good, the thermal boudary layer is quite big. On the other hand, I have used the wall temperature ( outer surface) and the results look closer to the expected, thinner. But my doubt is if I can use the wall temperature ( outer surface) to visualize the thermal bounday layer instead of the static temperature. Does anybody know the difference between the 2 methods?? Thanks!!

 March 21, 2012, 22:06 #2 New Member   Leandro Join Date: Mar 2012 Posts: 8 Rep Power: 7 and what about the velocity bounday layer? Does anybody know how to visualize ??? thanks once more

 March 22, 2012, 23:04 #3 New Member   Leandro Join Date: Mar 2012 Posts: 8 Rep Power: 7 Does anybody know?

 March 23, 2012, 10:28 #4 Member   Join Date: Nov 2011 Posts: 86 Rep Power: 8 The velocity boundary layer you can visualize it with normal velocity contours or vector plots. I don't think that the wall temperature can be used. I have no idea on how Fluent defines it. What is the value of your y+ at the wall? How you obtain the rotation of the cylinder? Cheers, Rob

March 24, 2012, 01:01
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Quote:
 Originally Posted by leomec88 Hello guys! I have been working in a simulation that consists in a air flow over a heated rotating cylinder. I' m trying to visualize the thermal boundary layer. I have used the Coutours- Static temperature, but the results doesn't look good, the thermal boudary layer is quite big. On the other hand, I have used the wall temperature ( outer surface) and the results look closer to the expected, thinner. But my doubt is if I can use the wall temperature ( outer surface) to visualize the thermal bounday layer instead of the static temperature. Does anybody know the difference between the 2 methods?? Thanks!!
For thermal boundary layer, plot static temperature was you were doing
For velocity boundary layer, you need to plot the appropriate velocity.

You shouldn't be using wall temperature, since that is a surface/wall condition and has nothing to do really with your fluid. Boundary layers strictly refer to the fluid profiles. Plot static temperature, the answer is there. It's possible the thermal boundary layer from the simulation is wrong if the simulation was poorly done. It's also possible the simulation is correct and that there is nothing wrong with the solution.

As an aside on the wall temperature and inner/outer surface business...
When energy is involved, the way the heated/cooled walls is handled is to apply two very thin solid regions very close to the wall. Two regions are necessary to define both the surface temperature and the surface heat flux. I forget how each surface is treated specifically but in general the two temperatures of the inner and outer surface are different. The difference in temperature is what provides the gradient in the solid necessary to drive the heat flux. Read the fluent manual if you're really interested in this aspect.

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