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-   -   Fully implicit scheme (http://www.cfd-online.com/Forums/openfoam/60798-fully-implicit-scheme.html)

johndeas June 24, 2008 12:14

Maybe a dumb question but... H
 
Maybe a dumb question but... How is it that Fluent is capable of fully-implicit time discretisation while OpenFOAM is not ?
Or, if put another way, what would be required to have fully-implicit time discretisation in OF ?

eugene June 24, 2008 12:39

What do you mean by "fully imp
 
What do you mean by "fully implicit" time discretization, and why do you think there is a difference between Fluent and OpenFOAM in this regard?

billy June 24, 2008 12:46

You would need to solve the eq
 
You would need to solve the equations of mass, momentum and energy simultaneously instead of segregated.

johndeas June 24, 2008 12:49

For example, you won't have li
 
For example, you won't have limitation on your Courant Number in Fluent.

This question arised as the Courant number can be a limitating factor and force you to have timesteps smaller than the one required by the eddy dissipation time.

eugene June 24, 2008 13:11

Most of the time schemes in Op
 
Most of the time schemes in OpenFOAM are "fully implicit". There are probably other things that Fluent does to run stable at very high CFL numbers.

On the other hand I regularly run LES with maximum CFL numbers of 2-3 without problems. It depends on the solver and your limiters I guess.

hjasak June 24, 2008 13:50

Sorry Eugene - time to read a
 
Sorry Eugene - time to read a book. The guy is talking about a block solution of the compressible flow system, which is "more implicit" than the segregated solution you are used to.

This is coming with my new block matrix implementation.

Hrv

liu June 24, 2008 13:59

Hrv, "This is coming with my
 
Hrv,
"This is coming with my new block matrix implementation"

When? I have been looking forward for this for a long time.

hjasak June 24, 2008 14:37

As you may have guessed, it is
 
As you may have guessed, it is all about funding: fully financed projects get priority, deadlines etc, meaning that interesting pieces of work get delayed.

It has been delayed for an inexcusable number of times, but it will make you happy to know that some people are already running block-coupled solutions.

Apologies for the delay,

Hrv

billy June 24, 2008 14:46

We should thank you for develo
 
We should thank you for developing such a great software!

liu June 24, 2008 18:23

Great! Hrv I should also th
 
Great! Hrv

I should also thank you for sharing.

pbohorquez June 25, 2008 08:40

Dear Hrv I wondered if the
 
Dear Hrv

I wondered if the community can enjoy such piece of work via the development version? This would be thankful news (among others).

Best wishes
Patricio


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