{"id":239267,"date":"2022-11-01T06:53:33","date_gmt":"2022-11-01T06:53:33","guid":{"rendered":"\/forum\/forums\/topic\/continuity-not-converging-in-steady-state-energy-equation-off\/"},"modified":"2022-11-01T06:53:33","modified_gmt":"2022-11-01T06:53:33","slug":"continuity-not-converging-in-steady-state-energy-equation-off","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/continuity-not-converging-in-steady-state-energy-equation-off\/","title":{"rendered":"Continuity not Converging in Steady State (Energy Equation OFF)"},"content":{"rendered":"

Hello all,<\/p>\n

I am running various temperature cases of some Fluent simulations. All residuals are set to 4e-4, except for energy which is set to 1e-6. I’m using a realizable k-epsilon model with enhanced wall treatment with under-relaxation. The method I am using for a “faster” simulation is to obtain the steady state conditions for velocity and pressure by only having the Flow and Turbulence equations ON under “Controls” (Energy is Off), then to switch to transient with Flow and Turbulence equations OFF and only Energy equation on. This allows Ansys to save the steady state results obtained and only calculate the unsteady results of temperature. For some reason, I am not able to get my continuity residuals low enough for convergence in steady state. I have experimented with trying all different Schemes overnight as well as trying different initialization methods\/solvers (momentum vs density-based) to no avail. I have over 2000+ iterations and the trend of the residuals for continuty seems to stay constant and have stopped dropping after a certain point. Strangely enough, I tested transient with a timestep size of 0.0001 seconds, with ALL three equations on and it converges okay, it’s just very time consuming.<\/p>\n

I am currently testing out a long transient run to see if I made a weird mistake with mesh interfaces but so far they look fine and I have heat transfer occuring through different bodies at reasonable rates. I increased my time step size to 0.01 seconds and each timestep converges within 100 iterations.<\/p>\n

 <\/p>\n

My current ideas are that<\/p>\n

A) maybe my mesh isn’t fine enough? But does being able to reach convergence in transient imply the mesh is fine enough, or is the solver “stricter” for steady state with energy equation off?<\/p>\n

B) I am running cases where the material properties of the fluid (air) change, would slightly altering the properties of air cause steady state to not be obtainable?<\/p>\n

C) My system may be inherritently unsteady which is why steady state convergence for continuity is so hard to obtain. <\/p>\n

 <\/p>\n

I am running Ansys 2021 R2. Sorry if I used any incorrect terminology, I’m still learning. <\/p>\n

Any help would be appreciated and I can provide more information or screenshots if needed.<\/p>\n

 <\/p>\n

-Rozina Nalbandian<\/p>\n

 <\/p>\n

 <\/p>\n

Screenshots:<\/p>\n

Current Mesh 3.4 million elements:<\/p>\n

<\/p>\n

<\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"template":"","class_list":["post-239267","topic","type-topic","status-closed","hentry","topic-tag-2021-r2","topic-tag-ansys-fluent","topic-tag-continuity-residuals-1","topic-tag-error","topic-tag-fluids","topic-tag-residual","topic-tag-troubleshooting"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["187106","199"],"_bbp_author_ip":["23.220.96.181"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["5774"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["239267"],"_bbp_forum_id":["27792"],"_bbp_engagement":["199","187106"],"_bbp_voice_count":["2"],"_bbp_reply_count":["3"],"_bbp_last_reply_id":["239945"],"_bbp_last_active_id":["239945"],"_bbp_last_active_time":["2022-11-07 10:36:33"]},"test":"rozinanalbandian"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/239267","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/239267\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=239267"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}