{"id":455787,"date":"2026-04-05T08:57:40","date_gmt":"2026-04-05T08:57:40","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/issue-with-continuity-residuals-when-using-time-varying-inlet-flow-udf-in-dynami\/"},"modified":"2026-04-05T08:57:40","modified_gmt":"2026-04-05T08:57:40","slug":"issue-with-continuity-residuals-when-using-time-varying-inlet-flow-udf-in-dynami","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/issue-with-continuity-residuals-when-using-time-varying-inlet-flow-udf-in-dynami\/","title":{"rendered":"Issue with Continuity Residuals When Using Time-Varying Inlet Flow UDF in Dynami"},"content":{"rendered":"

<p><\/p><p data-start=”85″ data-end=”204″>From the current setup, it can be observed that there are a chamber, a valve, an air port inlet, and a fuel port inlet.<\/p><p data-start=”206″ data-end=”527″>The objective of this study is to quantitatively evaluate the mixing quality as air and fuel enter the chamber. To achieve this, I attempted to implement the valve using a UDF with a dynamic mesh. Similarly, I applied a dynamic mesh at the bottom surface, like a piston, to create an expansion effect in the lower region.<\/p><p data-start=”529″ data-end=”809″>For the inlet conditions, I believed that assigning constant mass flow rates for both air and fuel would not be appropriate. Therefore, I implemented UDFs in which the mass flow rates follow a cosine function—starting low, reaching a peak in the middle, and then decreasing again.<\/p><p data-start=”811″ data-end=”1097″>However, when running the simulation with this setup, I observed that the continuity residual increases at every new time step. Although it eventually decreases back to a certain level, it rises again in the next step. This repetitive increase led me to believe that there is a problem.<\/p><p data-start=”1099″ data-end=”1316″>When I changed the air flow rate to a constant value, the continuity residual stabilized around 1. Based on this, I suspect that the way I implemented the time-varying flow rate using a UDF might be causing the issue.<\/p><p data-start=”1318″ data-end=”1485″>I would like to ask for your opinion on whether the UDF-based flow rate implementation could indeed be the source of the problem, and how this issue might be resolved.<\/p><\/p>\n","protected":false},"template":"","class_list":["post-455787","topic","type-topic","status-publish","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27792"],"_bbp_topic_id":["455787"],"_bbp_author_ip":["2001:2d8:8244:ad3b:a1f0:15a2:149a:809d"],"_bbp_last_reply_id":["0"],"_bbp_last_active_id":["455787"],"_bbp_last_active_time":["2026-04-05 08:57:40"],"_bbp_reply_count":["0"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["1"],"_bbp_engagement":["110365"],"_btv_view_count":["12"],"_bbp_topic_status":["unanswered"]},"test":"a1531318naver-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/455787","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\/455787\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=455787"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}