My FLUENT model includes fluid and solid regions, with Discrete-Ordinates (DO) radiation model.
The heating boundary conditions are defined by a named expression of Temperature-Time for the heating units. I'm having the issue that the temperatures in various parts of the model exceed the max value defined in the expression, even the heating units themselves.
The calculations completed normally.
What could be the possible causes?
Let's assume that during the calculation, the amount of heat generated by the heating element is first determined, and then the temperature field is calculated. If you do not calculate the temperature inside the heater and turn off the heating based on the surface temperature of the heater, then if the cooling conditions of the heating element worsen, the heat released at the previous stage will heat the heating element even after turning it off.
Its a bit of a guess without seeing the details of your model, but inherent to certain types of numerical simulation are feedback mechanisms that can lead to violations of the Discrete Maximum Principle. See the following or similar explanatory papers. This can sometimes be reduced by local mesh refinement, but again, that will be highly dependent on the details of your model.
https://www.tandfonline.com/doi/abs/10.1080/10407799308955890
Usually, temperature overshoots with radiation occur in skewed cells. Even if there is only one, then it propagates to the surrounding cells. So, maybe you can try to locally improve the mesh quality in the parts where this overshoot occurs.
Additionally, if it is not the case, ensuring that the angular discretization of the DO model is high enough (Theta and Phi divisions >= 3) could also help.
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