{"id":301836,"date":"2023-08-17T07:55:27","date_gmt":"2023-08-17T07:55:27","guid":{"rendered":"\/forum\/forums\/topic\/fluctuating-variables\/"},"modified":"2023-08-17T07:57:18","modified_gmt":"2023-08-17T07:57:18","slug":"fluctuating-variables","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/fluctuating-variables\/","title":{"rendered":"Fluctuating Variables"},"content":{"rendered":"Hi,<\/p>\n
I am trying to do CHT analysis of an exhaust manifold. Manifold geometry is not complex. I use polyhedral mesh and my mesh quality is sufficient. There is no sudden growth in cell size(i use grow rate 1.1). Some of my solver’s setups are:<\/p>\n
-Turbulence Model: SST k-w. (mesh is adjusted to reach y+ value under to 1)
-Coupled algorithm.
-Gradient: Green-Gauss Node Based
-Pseudo Time Method : Off
-Exhaust gas is defined as a ideal gas.
-Back Pressure is defined to outlet.<\/p>\n
I have 3 inlet and 1 outlet.<\/p>\n
I used hybrid initialization.
I started the analysis with first order and then switched second order(In the first order part, the analysis was converged and variables that i controlled were stabil.).
I iterated with decrease the courant number periodically.(from 200 to 1)
After switching to second order scheme residuals and variables started to fluctuate and fluctuation did not finish.<\/p>\n
What is the reason of fluctuation?
What is solution for convergence and stabilization?<\/p>\n
I added residuals and variables plots.<\/p>\n
Thanks,![\"\"](\"\/forum\/wp-content\/uploads\/sites\/2\/2023\/08\/17-08-2023-1692258533-variable1.png\")
<\/a>![\"\"](\"\/forum\/wp-content\/uploads\/sites\/2\/2023\/08\/17-08-2023-1692258564-variable2.png\")
<\/a>![\"\"](\"\/forum\/wp-content\/uploads\/sites\/2\/2023\/08\/17-08-2023-1692258575-variable3.png\")
<\/a>![\"\"](\"\/forum\/wp-content\/uploads\/sites\/2\/2023\/08\/17-08-2023-1692258592-variable4.png\")
<\/a>![\"\"](\"\/forum\/wp-content\/uploads\/sites\/2\/2023\/08\/17-08-2023-1692258519-residuals.png\")
<\/a><\/p>\n","protected":false},"template":"","class_list":["post-301836","topic","type-topic","status-closed","hentry","topic-tag-ansys-fluent","topic-tag-cht","topic-tag-conjugate-heat-transfer","topic-tag-fluent","topic-tag-fluid-solid-heat-transfer","topic-tag-numerical-instability-2"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["267437","15180","199842"],"_bbp_author_ip":["23.206.193.41"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["1277"],"_edit_lock":["1692258965:196608"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["301836"],"_bbp_forum_id":["27792"],"_bbp_engagement":["15180","199842","267437"],"_bbp_voice_count":["3"],"_bbp_reply_count":["7"],"_bbp_last_reply_id":["305999"],"_bbp_last_active_id":["305999"],"_bbp_last_active_time":["2023-09-11 06:33:43"]},"test":"ysfuznx1998gmail-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/301836","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\/301836\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=301836"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}