{"id":366539,"date":"2024-05-12T12:03:33","date_gmt":"2024-05-12T12:03:33","guid":{"rendered":"\/forum\/forums\/topic\/weird-behaviour-of-residuals-in-transient-simulation\/"},"modified":"2024-05-12T12:03:33","modified_gmt":"2024-05-12T12:03:33","slug":"weird-behaviour-of-residuals-in-transient-simulation","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/weird-behaviour-of-residuals-in-transient-simulation\/","title":{"rendered":"Weird Behaviour of Residuals in transient simulation"},"content":{"rendered":"<p>Hi, I&#8217;m trying to simulate supersonic flow (M=1.6) through a duct with shocks, first in steady state, then as a transient simulation by varying outlet pressure.<br \/>&nbsp;I was able to get a good and stable steady-state solution only after using high-speed numerics. After that i tried to run a transient simulation and used a udf to vary the outlet pressure sinusoidally. But I&#8217;m noticing a bizarre behaviour of residuals.<\/p>\n<p>During each iteration it is continuously increasing. The timestep I used is 1e-6, which I think is small enough for the frequency of oscillations of the outlet pressure (1000hz).<br \/>Some of the other settings are:&nbsp;<br \/><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/05\/12-05-2024-1715514692-mceclip0.png\"><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/05\/12-05-2024-1715514704-mceclip1.png\"><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/05\/12-05-2024-1715515264-mceclip4.png\"><br \/>Some other settings- pressure inlet, k-w sst model, density based solver.<br \/>Here is a picture of the residuals<br \/><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/05\/12-05-2024-1715515329-mceclip5.png\"><\/p>\n<p>And here is the dp\/dt contour from the exit,which looked pretty uniform at the start, looks weird and distorted after few iterations &#8211;&nbsp;<br \/><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/05\/12-05-2024-1715515061-mceclip3.png\"><br \/>I have been trying to figure out the reason for this problem since it seems like a pretty simple one but i haven&#8217;t been able to fix it. Is it because of some numerical problem, or some scheme i chose ? Kindly help, Thanks.<\/p>\n","protected":false},"template":"","class_list":["post-366539","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["288974","8124"],"_bbp_author_ip":["23.216.133.166"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["469"],"_bbp_topic_status":["unanswered"],"_bbp_likes_count":["1"],"_bbp_topic_id":["366539"],"_bbp_forum_id":["27792"],"_bbp_engagement":["8124","288974"],"_bbp_voice_count":["2"],"_bbp_reply_count":["4"],"_bbp_last_reply_id":["368758"],"_bbp_last_active_id":["368758"],"_bbp_last_active_time":["2024-05-27 16:39:44"]},"test":"ae22b001smail-iitm-ac-in"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/366539","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\/366539\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=366539"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}