{"id":392715,"date":"2024-11-05T07:34:40","date_gmt":"2024-11-05T07:34:40","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/turbulent-viscosity-ratio-and-convergence-issues\/"},"modified":"2024-11-05T07:34:40","modified_gmt":"2024-11-05T07:34:40","slug":"turbulent-viscosity-ratio-and-convergence-issues","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/turbulent-viscosity-ratio-and-convergence-issues\/","title":{"rendered":"turbulent viscosity ratio and convergence issues"},"content":{"rendered":"<p>&lt;p&gt;Hello,&nbsp;&lt;\/p&gt;&lt;p&gt;I am trying to simulation a shell side condensation with tubeside thermal BC in Fluent.&lt;\/p&gt;&lt;p&gt;Initially, i used the simple model to simulate and make the physics right and after achieving good results, i have gone into a little complex geometry.&lt;\/p&gt;&lt;p&gt;I have used the VOF-implicit model, k-epsilon and for around 20 30 timesteps(500 iterations), the simulation runs smooth and then reverse flow started in the domain, later after 10 20 timesteps (total of 1000+ iterations), turbulent viiscosity ratio started to appears in the simulation, its increases to a high value and then decreases to zero and repeat again until the solution gets diverge.&lt;\/p&gt;&lt;p&gt;1- I have tried to reduce under relaxation factors,&lt;\/p&gt;&lt;p&gt;2- Or tried to change the scheme from PISO to Simplec&lt;\/p&gt;&lt;p&gt;3- or reduce the timesteps size to min 6e-7 &amp; max 1e-5 with adaptive scheme (multiphase specific) where timestep size = min cell size \/ velocity is around 3e-5.&nbsp;&lt;\/p&gt;&lt;p&gt;4- Tried to change (3 &#8211; 4) geometry structure &amp; remesh it and simulate but this turbulent viscosity ratio and divergence is permanent.&nbsp;&lt;\/p&gt;&lt;p&gt;5- One thing to note is, the simulation is stable with Eulerian multiphase flow more then VOF but the turbulent viscosity ratio and divergence achieved within 5000-10000 iterations.&lt;\/p&gt;&lt;p&gt;&nbsp;&lt;\/p&gt;&lt;p&gt;I am not sure where is this thing going wrong as the same model works on a simpler geometry very well.&lt;\/p&gt;&lt;p&gt;Can you guide me here please.&lt;\/p&gt;<\/p>\n","protected":false},"template":"","class_list":["post-392715","topic","type-topic","status-publish","hentry","topic-tag-multiphase_models-1","topic-tag-divergence","topic-tag-divergence-detected","topic-tag-ImplicitVOF-1"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"Hello, I am trying to simulation a shell side condensation with tubeside thermal BC in Fluent.Initially, i used the simple model to simulate and make the physics right and after achieving good results, i have gone into a little complex geometry.I have used the VOF-implicit model, k-epsilon and for around 20 30 timesteps(500 iterations), the simulation\" \/>\n\t<meta name=\"robots\" content=\"max-image-preview:large\" 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