In ANSYS Fluent, the Nusselt number is not directly available as a predefined post-processing variable. However, you can calculate it using the temperature and velocity gradients at the wall manually.

You don't necessarily need to write custom code to calculate the Nusselt number. Instead, you can use Fluent's built-in functions to extract the necessary data, such as temperature and velocity profiles at the wall, and then perform the calculations manually using an external tool like Excel or MATLAB.

Alternatively, you can use Fluent's User Defined Functions (UDFs) to define custom expressions to calculate the Nusselt number within the software itself. This allows you to directly access the required variables and perform the calculations without exporting data to external software. @Omar Ennaya

Farnaz Hosseini thank you madame for your interaction

This is what i thought too, can you describe the steps to calculate the parameters needed to calculate the nusselt.

There's two temperatures: the wall temperature and the mean(or mixing) temperature, i wanna make sure what i did is correct(i used the report definitions option to do this).

There's something confusing me: to calculate the nusselt number we need the heat flux exchanged betweeen the wall and the fluid can you tell me how to calculate it in fluent cuz i'm not sure about what i did.

Thank you again for your feedback madame.