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-   -   Heat transfer modeling with kOmegaSST at walls (http://www.cfd-online.com/Forums/fluent/109674-heat-transfer-modeling-komegasst-walls.html)

Sören Sander November 23, 2012 07:54

Heat transfer modeling with kOmegaSST at walls
 
Hello everyone,

I try to figure out, how the heat transfer through a wall is calculated in fluent when using the kOmegaSST model. Unfortunately, there is nothing given in the fluent manuel. Is the laminar flow equation used, because yPlus is around 1?

LuckyTran November 25, 2012 20:12

Quote:

Originally Posted by Sören Sander (Post 393809)
Hello everyone,

I try to figure out, how the heat transfer through a wall is calculated in fluent when using the kOmegaSST model. Unfortunately, there is nothing given in the fluent manuel. Is the laminar flow equation used, because yPlus is around 1?

Fluent uses an enhanced wall function appropriate for kOmegaSST model for all equations (including energy). If your mesh is sufficiently fine near the wall (y+ < ~10), then it is equivalent to using the the linear (laminar) model.

Far November 26, 2012 01:16

Yes, with Y+1 you are able to solve the laminar sublayer.

Sören Sander November 28, 2012 05:01

Thanks for your replys. However, now I have found another problem on this topic:

I want to calculate the heat transfer coefficient. fluent can derive it automatically, but again I am not able to find the formulation.

It should be h=(T_wall-T_inf)/q_dot, where q_dot=(T_wall-T_p)/dn
where T_p is the temperature derived in the first cell from the wall and dn is the distance normal from the wall. What value does T_inf have? Is it the same as T_p? Is there any reference to validate how it is calculated?

LuckyTran November 28, 2012 09:35

Quote:

Originally Posted by Sören Sander (Post 394587)
It should be h=(T_wall-T_inf)/q_dot, where q_dot=(T_wall-T_p)/dn
where T_p is the temperature derived in the first cell from the wall and dn is the distance normal from the wall. What value does T_inf have? Is it the same as T_p? Is there any reference to validate how it is calculated?

T_inf should be the driving fluid temperature consistent with Newton's law of cooling. Things like freestream temperature, bulk temperature, recovery temperature are used to get the most physical value of h. T_inf is using nomenclature from low-speed external flows where the freestream temperature is the driving temperature. Otherwise the choice of T_inf is arbitrary as much as length scale is arbitrary in Reynolds number.

Sören Sander November 28, 2012 11:34

So I can define T_inf in fluent?

LuckyTran November 28, 2012 11:58

Quote:

Originally Posted by Sören Sander (Post 394680)
So I can define T_inf in fluent?

Oh yes. T_inf is a user supplied input. It is the reference temperature that is user specified in the reference values. It is specified as a constant. If you want to use a variable T_inf you will need to modify the fluent code (use a UDF).

The wall heat flux and surface temperature are determined from the solution. The heat transfer coefficient is then calculated by applying Newton's law of cooling and using Tref (the reference temperature specified in the reference values).


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