Changing from explicit to implicit ????

ReCr · November 13, 2014, 12:02

My professor keeps asking us to go through the tutorials and run the same trial but switch from implicit to explicit to see how the results vary. But everything I have read online and in the user guide suggest this can't be done...I'm i right or is my professor?

ghorrocks · November 13, 2014, 17:20

Switch between implicit and explicit for what? There are many different parts of the CFD solver and some are implicit and some are explicit. But if you mean the main pressure-momentum coupling equations (ie the Navier Stokes solver) then CFX is an implicit solver and has no explicit option.

ReCr · November 13, 2014, 17:57

I'm assuming that he meant for solving the NS equations. The only other way to change between explicit and implicit would be for the turbulence, Correct?

ghorrocks · November 13, 2014, 20:01

No, turbulence is implicitly included in the solution. It is solved in a separate matrix so it is loosely coupled with the NS equations but still is implicit.

I think I got my wires crossed there. Fluent allows selection of several implicit or explicit options, including for the NS equations and for several multiphase models as well. I do not think CFX has an explicit option of any model that comes to mind.

sircorp · June 8, 2015, 08:16

Quote:

Originally Posted by ghorrocks

No, turbulence is implicitly included in the solution. It is solved in a separate matrix so it is loosely coupled with the NS equations but still is implicit.

I think I got my wires crossed there. Fluent allows selection of several implicit or explicit options, including for the NS equations and for several multiphase models as well. I do not think CFX has an explicit option of any model that comes to mind.

Interesting : (Only for Fluent Users : I am not an expert, just tying to find quicker way to solve Density Based Implicit Method in Fluent).

Question is ? Can I stop half way through an implicit method and switch to explicit method ? Will it save time ? (assuming I use current value from implicit method in explicit method ) ?

Shane

ghorrocks · June 8, 2015, 19:44

No idea. Try asking on the Fluent forum.

November 13, 2014, 12:02	Changing from explicit to implicit ????	#1
ReCr New Member Adam Join Date: Nov 2014 Posts: 6 Rep Power: 11	My professor keeps asking us to go through the tutorials and run the same trial but switch from implicit to explicit to see how the results vary. But everything I have read online and in the user guide suggest this can't be done...I'm i right or is my professor?

November 13, 2014, 20:01		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	No, turbulence is implicitly included in the solution. It is solved in a separate matrix so it is loosely coupled with the NS equations but still is implicit. I think I got my wires crossed there. Fluent allows selection of several implicit or explicit options, including for the NS equations and for several multiphase models as well. I do not think CFX has an explicit option of any model that comes to mind. sircorp likes this.

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November 13, 2014, 17:20		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Switch between implicit and explicit for what? There are many different parts of the CFD solver and some are implicit and some are explicit. But if you mean the main pressure-momentum coupling equations (ie the Navier Stokes solver) then CFX is an implicit solver and has no explicit option.

November 13, 2014, 17:57		#3
ReCr New Member Adam Join Date: Nov 2014 Posts: 6 Rep Power: 11	I'm assuming that he meant for solving the NS equations. The only other way to change between explicit and implicit would be for the turbulence, Correct?

June 8, 2015, 19:44		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	No idea. Try asking on the Fluent forum.