{"id":391327,"date":"2024-10-25T04:16:29","date_gmt":"2024-10-25T04:16:29","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/issue-with-specific-flux-boundary-condition-at-inlet-for-uds-transport\/"},"modified":"2024-10-25T04:16:29","modified_gmt":"2024-10-25T04:16:29","slug":"issue-with-specific-flux-boundary-condition-at-inlet-for-uds-transport","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/issue-with-specific-flux-boundary-condition-at-inlet-for-uds-transport\/","title":{"rendered":"Issue with Specific Flux Boundary Condition at Inlet for UDS Transport"},"content":{"rendered":"<p>&lt;p&gt;I am trying to solve the transport equation for a user-defined scalar (UDS) representing the number of particles in a single-phase flow, with velocity at the inlet and zero pressure at the outlet. The flux function I am using is the mass flow rate.&lt;\/p&gt;&lt;p&gt;At the inlet, the particles are released at a rate specified as the number of particles per unit area per unit time (flux). The inlet concentration of RP is 2.5 &times; 10^14 particles\/m&sup3; and the inlet concentration of AP is 1.25 &times; 10^13 particles\/m&sup3;.&lt;\/p&gt;&lt;p&gt;I am defining the specific flux at the inlet as:&lt;\/p&gt;&lt;p&gt;<code>-1 &times; UDS diffusivity &times; grad(UDS) &sdot; n<\/code>&lt;\/p&gt;&lt;p&gt;with units of kg\/(m&sdot;s) &times; particles\/m&sup3; &times; m\u207b&sup1;.&lt;\/p&gt;&lt;p&gt;i conduct it by ufd profile like this&lt;\/p&gt;&lt;p&gt;<img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/10\/25-10-2024-1729829628-01.PNG\" alt=\"\" \/>&lt;\/p&gt;&lt;p&gt;When I apply this specific flux model, my simulation crashes. However, when I set a specific value of 2.5 &times; 10^14 for RP and 1.25 &times; 10^13 for AP at the inlet, it runs but I am unsure if it is working correctly.&lt;\/p&gt;&lt;p&gt;Can you help me understand why the specific flux model causes the crash and whether I am correctly setting up the boundary conditions for the UDS?&lt;\/p&gt;<\/p>\n","protected":false},"template":"","class_list":["post-391327","topic","type-topic","status-publish","hentry","topic-tag-udf"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"I am trying to solve the transport equation for a user-defined scalar (UDS) representing the number of particles in a single-phase flow, with velocity at the inlet and zero pressure at the outlet. 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