[Pyrokrates]

Hey,


short (and maybe simple) question. I wold like to use scalar transport equation with an source term which is a function of my scalar itself meaning:

dC/dt + v * grad(C) = - alpha * C

So if I understand the manual correctly my source which I return would be:

 source = - alpha * C

while my implicit part would be as follows:

ds[eqn] = - alpha

Problem here for me is, that the explicit source part is stil a function of my scalar value, which is zero in every cell at the beginning and only defined at inlet boundary faces. Another problem for me is, when calling DEFINE_SOURCE, I need to set a value for C but from my understanding, for solving the equation implicit, I don´t need to set C because it should be the C from next time step and not the old one.


Thanks for any help in advance


Chris

[AlexanderZ]

from my understanding there are two options for you:
1. use DEFINE_INIT function to set your scalar values (C = 0, as you told)
2. initialize steady state simulation, patch your scalar = 0, everywhere. On BC you put some value explicitly anyway. Calculate -> so you will get some scalar distribution.
Switch to transient, continue simulation

[Pyrokrates]

Hi and thank you for the quick answer.


Sorry but I don´t understand, what´s the advantage of 1. for my code...
If I´m using UDS, it should be initialize with zero everywhere... And under boundary conditions in fluent, I can define the value at the inlet... But my problem is that if I give a value of my cells to the source it is the one from previous step and not explicit? Isn´t a fully implicit source term possible?


I have also done some simulations using OpenFOAM and there I can just define if fully implicit.


Thanks in advance


Chris