

November 26, 2020 at 10:17 pmmanelaero2020Subscriber
Hello evry one ;
I am simulating a swirling flow inside a cyclonic filter.
I have tried two turbulence models :
1/ Standard K_Epsilon
2/ Kepsilon RNG Swirling flow ( this is the most appropriate for swirling flows)
Methods are :
3/ Simple for velocity pressure coupling For both turbulence models
4/Upwind second order for turbulence , mass , momentum  For both turbulence models
Calculation with the standard K epsilon model , has converged after 280 itÃ©rations
But Calculation with the K epsilon RNG swirling flow model has not converged , the residus curve continued to oscillate ( instable) even aftre 6000 iterations ( a time of 1:30 h) . I have stopped calculation , because i have concluded that solution will not converge , i will just waste my time.
For more details , please see figures attached.
Since RNG Swirling flow is better than k epsilon to model cyclone inside filter , i prefer using it rather than standar k epsilon model.
I ask you please :
A/ Can you find an explanation about why the residus curve oscillates continually and solution has not converged even after more than 6000 iterations ?
B/ Advice me to change something ? in the order to accelerate convergence of the model ?
Remark : I have tried to reduce the value of residus from 0.001 to 0.01 but , also used Quick Scheme instead of simple but the problem is always here
Thanks tou very much
Kind regards

November 27, 2020 at 11:42 amFederico2594SubscriberHi Aero2020,nDo you have evaluate your mesh?nI think probably that the mesh is not good to describe your phisic problem. Are you in Grid Indipendent solution?nDo you have evaluate your y+ for your turbolence model? Is the inflation layer correct? nDo you begin the calculation with first order to prepare the solution field and than change to second order?nWithout being presumptuous i think you have to see the theory before and then start the calculation.nRegards,nFedericon

November 27, 2020 at 11:50 amRobForum ModeratorRead up on precessing vortex cores: you've probably refined the mesh sufficiently to pick up the transients in the flow field. Also have a look at the model limitations for ke and kw models in highly swirling flows: hint, read up on the Reynolds Stress Model. nmakes good points; in this case y+ is less important as the complex flow is away from the wall: so you need to resolve the volume as well as the near wall. You also want to look at using a hex or poly mesh. n

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