{"id":408466,"date":"2025-02-05T11:19:48","date_gmt":"2025-02-05T11:19:48","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/mixing-of-tracer-with-free-surface-in-stirred-tank-concentration-keeps-rising\/"},"modified":"2025-02-05T11:19:48","modified_gmt":"2025-02-05T11:19:48","slug":"mixing-of-tracer-with-free-surface-in-stirred-tank-concentration-keeps-rising","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/mixing-of-tracer-with-free-surface-in-stirred-tank-concentration-keeps-rising\/","title":{"rendered":"Mixing of Tracer With Free Surface In Stirred Tank &#8211; Concentration Keeps Rising"},"content":{"rendered":"<p>&lt;p&gt;Hi,&lt;\/p&gt;&lt;p&gt;I am attempting to model mixing of tracer in a stirred tank with a free surface (air-water interface, vortex shape forms). I have first computed the free surface of the liquid using VOF solver. I then patched in 2 mL of tracer into the liquid (2.65 L), assuming that the properties of the tracer are the same as the liquid phase and tracer does not disturb the flow so I can switch off all the equations and solve only for species transport.&lt;\/p&gt;&lt;p&gt;I have patched 30 g\/L of tracer for the 2 mL volume by initialising the mass fraction.&nbsp;&lt;\/p&gt;&lt;p&gt;<img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2025\/02\/05-02-2025-1738753657-mceclip0.jpg\" \/>&lt;\/p&gt;&lt;p&gt;What I am noticing is that during the simulation run, the concentration of tracer initially decreases as the tracer is dispersing in the liquid (should be expected due to mixing) but then suddenly increases to a large value of 760 g\/L and the concentration profile shows an inflection and begins to increase rapidly rather than reach a steady value. I am unsure as to what is causing this behaviour as I have tried the same methodology for single phase simulation (assuming flat liquid surface) and it works as expected. Unless I have set up something wrong (and I have repeatedly checked my simulation set-up), then I am struggling to understand what is causing this rapid change in tracer concentration when I have a vortex and not flat liquid surface?&lt;\/p&gt;&lt;p&gt;<img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2025\/02\/05-02-2025-1738754082-mceclip2.jpg\" \/><img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2025\/02\/05-02-2025-1738754076-mceclip1.jpg\" \/>&lt;\/p&gt;<\/p>\n","protected":false},"template":"","class_list":["post-408466","topic","type-topic","status-publish","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27792"],"_bbp_topic_id":["408466"],"_bbp_subscription":["282802","199"],"_bbp_author_ip":["129.11.113.4"],"_bbp_last_reply_id":["422963"],"_bbp_last_active_id":["422963"],"_bbp_last_active_time":["2025-02-24 09:42:14"],"_bbp_reply_count":["30"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["2"],"_bbp_engagement":["282802","199"],"_btv_view_count":["466"],"_bbp_topic_status":["unanswered"]},"test":"ll17s5rleeds-ac-uk"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/408466","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\/408466\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=408466"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}