{"id":295212,"date":"2023-07-27T16:29:40","date_gmt":"2023-07-27T16:29:40","guid":{"rendered":"\/forum\/forums\/topic\/convergence-issues-with-nist-real-gas-modell-at-increasing-velocity-inlet\/"},"modified":"2023-07-27T16:29:40","modified_gmt":"2023-07-27T16:29:40","slug":"convergence-issues-with-nist-real-gas-modell-at-increasing-velocity-inlet","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/convergence-issues-with-nist-real-gas-modell-at-increasing-velocity-inlet\/","title":{"rendered":"Convergence issues with NIST real gas modell at increasing velocity inlet"},"content":{"rendered":"<p>Hello everyone, Im studying an airflow inside a finned tubular heat exchanger at various inlet velocities in Fluent with real gas model. Starting at 10 ms inlet velocity it runs smoothly and converges (and i get right results) but with increasing velocity it starts to diverge (at 12,5ms) and i just cant explain why. Ive tried many different things: k-epsilon and omega SST models, enhanced wall treatment or without, different inlet turbulence intensities and settings (initial pressure), restricted backflow reversal, lower relaxation factors, etc.. Im using NIST real gas model of air. My initial guess was that it has to do with the mesh quality and y+ value, but after doubling the number of cells i still get the same results. Ideal gas model works fine at even larger velocities. Analyzing the results, my turbulent Reynolds number just skyrockets at the end of the domain and the inlet pressure is way too low (around -20kPa when I have 0Pa outlet condition doesnt make any sense, it should be around 5kPa). Furthermore if i put mass flow inlet corresponding to the approximate value for the same velocity, the simulation converges normally. Is there a problem with NIST real gas model and velocity inlet? And why does it happen at a such specific velocity value? I would appreciate any help .<\/p>\n","protected":false},"template":"","class_list":["post-295212","topic","type-topic","status-closed","hentry","topic-tag-fluent-cfd-ansys-1","topic-tag-fluent"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["290309","199"],"_bbp_author_ip":["23.206.193.154"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["657"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["295212"],"_bbp_forum_id":["27792"],"_bbp_engagement":["199","290309"],"_bbp_voice_count":["2"],"_bbp_reply_count":["6"],"_bbp_last_reply_id":["295702"],"_bbp_last_active_id":["295702"],"_bbp_last_active_time":["2023-07-31 15:41:06"]},"test":"tanasovcampus-tu-berlin-de"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/295212","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\/295212\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=295212"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}