Learning Forum

[DongwooChoi]

Hello, I'm little confused about temperature settings.

When I set initialization temperature of 290K in contained fluid like picture below, fluid's temperature became 290K

[Rob]

The initialisation value is just that, it's the value in the domain at iteration 0, ie before you start solving the model.
The boundary condition is the value added to the domain from that boundary.
As the solvers are iterative we need a first "guess" at the solution. The solver takes that and then uses the boundary settings, models etc to calculate the solution. In steady state the initial condition wants to be sensible but generally doesn't have much impact on the solution (pressure in and pressure out with compressible flow is an exception - you need a good starting solution). In the transient case the solver also adds time into the mix, so a silly initial condition may take many time steps to be removed from the results.

[DongwooChoi]

Thank you for replying! (I'm sorry about Duplicated post I thought that was deleted)

I initially thought initialisation value is just for guessing solution(as you said), so whatever I enter at there, I thought maybe there could be difference in calculation time, but there should be no difference at fluid's initial temperature.
But when I enter 200K at initialisation temperature, fluid's initial temperature became 200K, when I enter 300K, fluid temperature start from 300K.
So, I thought it might be setting for initial(at 0second) temperature.
It still makes me little bit confusing.
Can you give me some light ?

[Rob]

Initial temperature is the setting for t=0 assuming you use the standard initialisation or patch. In your model I might patch the gas region at 200K and the solid at 500K as my starting point. I'll then watch the hot bit cool down and the cold bit warm up over the solution.
Material entering the domain will take the boundary temperature. So an inlet temperature of 250K means air will enter the domain at 250K. If you set a wall temperature, the wall will be that temperature and the neighbouring fluid will slowly move towards the same value.

[DongwooChoi]

Thank you very much, sir