[Mondal131211]

Dear Foamers,


What is the process of calculating Nusselt number from OpenFoam simulations. I am simulating natural convection along a vertical plate using buoyantPimpleFoam (OpenFoam Version 3.0.1). Is it possible to find it by putting function inside the controlDict?

Any help will be appreciated.



Thank You in advance...


Cheers,
Razon

[Eldrael]

Hello Mondal:

Take a look at this.

You might get the same result playing a little bit with wallHeatFlux and the rest of the functionObjects.

[Mondal131211]

Originally Posted by Eldrael

Hello Mondal:

Take a look at this.

You might get the same result playing a little bit with wallHeatFlux and the rest of the functionObjects.

Hi Eldrael,


First of all, thank you for your response. I tried several times in the above process but could not successfully compiling. Here I attached my edited NusseltCalc file and error image. Can you help me please?


Cheers,
Razon

[Eldrael]

Hello Mondal:

I am sorry to say I am not very familiar with the solver that you are posting, C++ nor OpenFOAM coding.

Thing is that you may not need to do it. Let's review how to calculate the Nusselt:

Nu= h L/ k; where the only thing not known in here is the h coefficient, as L is chosen by the user and k is a physical property of the fluid.
h coefficient has an arbitrary definition as the number fulfilling that Q=hA(Tfluid-Twall). Tfluid is set as a "bulk" temperature, so you choose it yourself.

If you are in an incompressible solver you can calculate h by using typing

*typeHereYourSolver* -postProcess -func wallHeatTransferCoeff

which is more like a local approximation, as you will not have imputed Tfluid. As it will be written on a filed, use a function object to average it.

The alternative is to use function objects to:

• Calculate Q with this or quickly approximate it with gradient(T) *k at the wall vicinity.
• Average both your calculation of Q and of temperature at the wall.

At the end of the second step you would have the total heat Q, the area (which is calculated by the function objects) and the average temperature of the wall. Then, calculate h with its definition. Finally, enter with it into the Nusselt definition.

[agustinvo]

Hi,
I normally do it later, during the post processing. What you will need to extract is the wall temperature gradient.

[Mondal131211]

Originally Posted by agustinvo

Hi,
I normally do it later, during the post processing. What you will need to extract is the wall temperature gradient.

Hi Agustinvo,

Thank you for joining in this conversation. Actually, I want to calculate the Nusselt number along the wall or from the whole computational domain. How did you do that? If I want to calculate the nusselt number for the whole domain, what is process of doing that after simulation? Can you please explain it?

Cheers,
Razon

[agustinvo]

Originally Posted by Mondal131211

Hi Agustinvo,

Thank you for joining in this conversation. Actually, I want to calculate the Nusselt number along the wall or from the whole computational domain. How did you do that? If I want to calculate the nusselt number for the whole domain, what is process of doing that after simulation? Can you please explain it?

Cheers,
Razon

Hi Razon,

what I did, I developed a functionObject to get the wall temperature gradient (starting from the wallShearStress one, you have few modifications to do), and using it you can get the Nusselt as





where L is the wall coordinate. I suppose that, for the Nusselt within the fluid (does somebody uses that quantity) you should use the temperature gradient there.