Learning Forum

[manelaero2020]

Hello evry one ;

I am simulating a swirling flow inside a cyclonic filter.

I have tried two turbulence models :

1/ Standard K_Epsilon

2/ K-epsilon -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 itérations

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

[Federico2594]

Hi 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

[Rob]

Read 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 k-e and k-w 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