initialisation in CFX
 

I am just wondering if I don't set up any initialisation, what initial conditions will be used in CFX simulation. many thanks

littlelz

If you don't initialize a problem it takes some more time to get converge.with out initialization you can run a problem

thanks. that's exactly what I experienced. I need more time to get converged result. I can run the problem without initialisation. however, I guess CFX must have some estimated initialisation in order to start the running although we don't know exactly what they are.

I am running one problem with M=0.25. If I set nothing for initialisation, it will fail because of overflow. however, if I set freestream conditions as initial data, it will converged very quickly.

for another case with M=0.8, without initialisation, it can be converged, but need longer time, with some initial setting, it can be converged quickly.

could anyboday give me some explaination on it?

many thanks

littlelz

for any numerical method you need to provide a starting point for the calculations. obviously the closer you are to the solution the faster the process. CFD is no different and choosing realistic initial conditions for your problem will yield to faster convergence. I think the solver will use default initial values for variables if an initialization setup is missing; although I have to say I might be wrong as I dint test the above and I don't particularly try to make my life difficult on purpose.

If you don't specify anything CFX uses zero for all variables everywhere. For simple stuff this is OK, but tricky simulations need a better guess than this to get started.

thanks guys,

your reply are very helpful. many thanks.

littlelz