TRANSIENT HEAT TRANSFER - SOLVE STAGE 2 INQUIRY

[mar.wen]

Please refer to this tutorial:

https://help.autodesk.com/view/SCDSE/2021/ENU/?guid=GUID-404667FB-869A-412D-BE50-D2B70905E28C

At "Solve Stage 2"; the Flow was turned off and the Heat transfer turned ON.

My question is that this set-up assumed that the flow previously set up is still running?

And the reason for this is that the set-up was divided into 2 phases?

If we will plan to run it in 1 stage then we will turn both the Flow and heat transfer ON?

Am I right with my comprehension?

[karol.suchon]

Hello.

In that case, we need to divergence the solution by two steps because it is a transient heat simulation.

We need the calculated velocity field before we run the transient thermal to get stable heat exchange boundary conditions between the fluid and solid. You could imagine that in the real world the solution also does not start from the velocity equal to 0.

If we turned off the flow in physics, the flow works as being "frozen". So the flow parameter will be not changed.

If we have the velocity field calculated and we do not expect the natural convection, the velocity field will do not change and we could compute only heat transfer. heat transfer will use previously calculated velocity etc.

If you have any questions feel free to ask.

Best regards,

Karol

[mar.wen]

Thank you for the explanation but I have a follow-up question on this explanation of yours:
"If we have the velocity field calculated and we do not expect the natural convection, the velocity field will do not change and we could compute only heat transfer. heat transfer will use previously calculated velocity etc."

Do you mean that there should be no natural convection on the set-up or this part of the assumption? I asked because there is natural convection for the outer surfaces of my set-up and also on the tutorial, the film coefficient was specified (natural convection).
https://help.autodesk.com/view/SCDSE/2021/ENU/?guid=GUID-7AF0A530-67CA-405F-8C94-DEFFD595DBA0

[karol.suchon · Accepted solution]

The boundary conditions applied only tell about the heat exchange conditions, but the fluid velocity is high enough to get the forced convection near that surface. So the BC are fine but overall they will do not have an influence on the velocity field results, so there is no reason to compute it once again. The situation will look different if you have a much lower velocity on the inlet. If you are still not sure about it, you could run the simulation with the flow and variable air with a proper gravity vector to compare the results.

Best regards,
Karol