Divergence while using RSM turbulence model

Bharatt · June 16, 2012, 05:18

Hello everyone,

i am running a simulation for different turbulence models for an airfoil. I am facing AMG divergence or sometimes FLOATING ERROR: OVERFLOW when i am shifting to RSM turbulence model.
the procedure i am following is achieving convergence in K-epsilon at first place and then shifting to RSM, the following parameters i used in initial(K-epsilon) stage.

Solver:- pressure based, Green-gauss node based
Viscous:- Standard K-epsilon
Boundary conditions(under turbulence):- K and epsilon
Scheme:- SIMPLE 1st order for 100 iterations then 2nd order(URF:- momentum reduced to 0.5 from 2nd order)

By about 4000 iterations convergence is achieved.
NOW, i go back to viscous:-
under solver-->viscous:- RSM, linear pressure strain etc and rest kept the same(parameters which i used for k-epsilon).

By about 100 iterations AMG divergence occurred

P.S:- please correct me if i am doing anything wrong!
-do i have to initialize it again?

thanks in advance

bharat

meangreen · July 18, 2012, 19:23

You don't have to initialize again, you can use the solution from k-epsilon to converge with RSM.

I wonder if you are running into issues with your boundary conditions. Are you checking your Y+ values at the walls?

Bharatt · July 19, 2012, 06:16

Hey Casey,

Thanks for your comments. i'll keep that point in mind.
and yes i am checking for y+ values.

bharat

Rami · July 23, 2012, 06:16

Smells like a Fluent simulation to me. If so - why don't you post it in the Fluent-dedicated forum?

June 16, 2012, 05:18	Divergence while using RSM turbulence model	#1
Bharatt Member Bharat Join Date: Jul 2011 Location: Delhi, India Posts: 49 Rep Power: 15	Hello everyone, i am running a simulation for different turbulence models for an airfoil. I am facing AMG divergence or sometimes FLOATING ERROR: OVERFLOW when i am shifting to RSM turbulence model. the procedure i am following is achieving convergence in K-epsilon at first place and then shifting to RSM, the following parameters i used in initial(K-epsilon) stage. Solver:- pressure based, Green-gauss node based Viscous:- Standard K-epsilon Boundary conditions(under turbulence):- K and epsilon Scheme:- SIMPLE 1st order for 100 iterations then 2nd order(URF:- momentum reduced to 0.5 from 2nd order) By about 4000 iterations convergence is achieved. NOW, i go back to viscous:- under solver-->viscous:- RSM, linear pressure strain etc and rest kept the same(parameters which i used for k-epsilon). By about 100 iterations AMG divergence occurred P.S:- please correct me if i am doing anything wrong! -do i have to initialize it again? thanks in advance bharat

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July 18, 2012, 19:23		#2
meangreen Member Casey Join Date: Jun 2009 Posts: 98 Rep Power: 17	You don't have to initialize again, you can use the solution from k-epsilon to converge with RSM. I wonder if you are running into issues with your boundary conditions. Are you checking your Y+ values at the walls?

July 19, 2012, 06:16		#3
Bharatt Member Bharat Join Date: Jul 2011 Location: Delhi, India Posts: 49 Rep Power: 15	Hey Casey, Thanks for your comments. i'll keep that point in mind. and yes i am checking for y+ values. bharat

July 23, 2012, 06:16		#4
Rami Senior Member Rami Ben-Zvi Join Date: Mar 2009 Posts: 155 Rep Power: 17	Smells like a Fluent simulation to me. If so - why don't you post it in the Fluent-dedicated forum?