Hello to everyone.
I recently asked about the same topic, thinking everything worked and I was just in need of the correct report; it was not correct.
My goal were to make a transient simulation of a brake disk, starting at t=0 with a certain temperature, let the air stream cool it down and see in how much time it reaches the goal (lower) temperature.
So, about the problem: I have a simple brake disk with a surrounding enclosure, no Boolean Substract in order to keep my disk as a "solid" inside the enclosure and assign it the material; set up all what i needed to make a basic flow simulation, but i'm having problems with the thermal part.
After some researches, I thought it was just necessary to set up a transient simulation with the energy equation on, initializate and then patch my disk region with the initial temperature and then let it simulate. But the disk temperature stay at the imposed temperature.
Where did I do wrong?
Thank you for any suggestion.
Hi,
do you have connected the fluid part (zone) of your simulation with the solid part (zone) by an interface where you allow Fluent to calculate the heat flux over that interface?
Regards,
Dr. Th. Frank.
Hi Dr. Frank and thanks for the answer.
I didn't because thought the mesher did it by itself, as in other simulations did.
But, looking at it right now, I don't see any interface. Maybe something changed while I was try and error.
If i'm not wrong I should create it in the Mesher, but how?
Regards,
Edoardo Frinconi
The interface between a solid and a fluid zone is not a meshing issue. It is setting a physical model for the solver on how to deal with heat transfer at this mesh interface.
It is different from just having 2 adjacent pieces of mesh in a fluid domain, where such a mesh interface would be silently treated as an interior boundary between two fluid zones.
And of course you need to solve an energy equation in the solid zone, if not yet done already.
Regards,
Dr. Th. Frank.
Thanks for the suggestion. Looked online and seems now it recognizes the interface: as the simulation goes on, the temperature is finally changing.
Badly that in the first 4 time steps it went from the starting 300°C to -400 to 2000 in the 4th. I guess there's still something wrong, but maybe it's just normalizing and I need to wait the end of the simulation?
I would guess, that this is some kind of numerical instability and that the result is already close to garbage. Maybe caused by a too large timestep of the simulation and too strong temperature gradients.
In particular in transient simulations it is absolutely important, that each individual timestep is converging to the target. Otherwise the end result is wrong, since the intermediate integral balances are not satisfied anymore.
Regards,
Dr. Th. Frank.
It was, thanks for the suggestion!
I've set 30 iterations x time step and reduced a bit all the parameters of relaxation factors from the default values. Now it's going perfectly fine!
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