{"id":459858,"date":"2026-06-16T13:15:10","date_gmt":"2026-06-16T13:15:10","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/how-to-simulate-the-fluid-penetration-through-the-wall-without-using-porous-jump\/"},"modified":"2026-06-16T13:15:10","modified_gmt":"2026-06-16T13:15:10","slug":"how-to-simulate-the-fluid-penetration-through-the-wall-without-using-porous-jump","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/how-to-simulate-the-fluid-penetration-through-the-wall-without-using-porous-jump\/","title":{"rendered":"How to simulate the fluid penetration through the wall without using porous jump"},"content":{"rendered":"

<p>Hi everyone,<\/p><p class=”ds-markdown-paragraph”><span class=””>I am currently working on a biomechanical simulation involving a flexible hose that undergoes large rotational motion and significant flexible deformation. My primary objective is to simulate fluid seepage (leakage) through micro-pores distributed along the wall of this hose, while accurately capturing the two-way Fluid-Structure Interaction (FSI) between the internal flow and the deforming solid structure. I am using <\/span><span class=””>ANSYS System Coupling<\/span><\/strong><span class=””> to handle the bidirectional coupling (Fluent + Mechanical).<\/span><\/p><p class=”ds-markdown-paragraph”><span class=””>My Initial Approach & The Bottleneck:<\/span><\/strong><br><span class=””>To model the porous seepage, I initially extended the fluid domain by adding a thin porous zone adjacent to the inner wall and applied a <\/span><span class=””>”Porous Jump”<\/span><\/strong><span class=””> boundary condition at the interface. However, this geometric modification has proven to be highly problematic for the FSI process. Because the hose deforms and rotates, the additional porous region requires complex mesh motion and, more critically, introduces a massive amount of additional mapping\/interpolation at the FSI interface. This significantly increases the computational cost and severely deteriorates the convergence stability of the coupling iterations.<\/span><\/p><p class=”ds-markdown-paragraph”><span class=””>The Core Question:<\/span><\/strong><br><span class=””>I would like to eliminate the extended domain and the “Porous Jump” condition altogether. <\/span><span class=””>Is it possible to implement this seepage effect directly on the original, unchanged wall boundary (i.e., keeping the default no-slip wall topology) using a User-Defined Function (UDF)?<\/span><\/strong><\/p><p class=”ds-markdown-paragraph”><span class=””>Specifically, I am looking for a UDF that can impose a local mass flux or velocity normal to the wall (simulating the seepage) directly on the wall faces, <\/span><span class=””>without<\/span><\/em><span class=””> changing the boundary type from “Wall” in the Fluent GUI. The boundary should simultaneously:<\/span><\/p><\/p>\n

    \n
  1. <p class=”ds-markdown-paragraph”><span class=””>Act as a standard wall for the tangential flow (no-slip).<\/span><\/p><\/li>\n
  2. <p class=”ds-markdown-paragraph”><span class=””>Allow a specified normal outflow (seepage) driven by the local pressure gradient.<\/span><\/p><\/li>\n
  3. <p class=”ds-markdown-paragraph”><span class=””>Maintain the exact same geometric face zones so that the FSI load transfer (pressure and viscous forces to Mechanical) remains straightforward and does not require additional mapping interfaces.<\/span><\/p><\/li>\n<\/ol>\n

    <p class=”ds-markdown-paragraph”><span class=””>Specific Inquiries:<\/span><\/strong><\/p><\/p>\n

      \n
    1. <p class=”ds-markdown-paragraph”><span class=””>Which UDF macro is most suitable for this purpose?<\/span><span class=””> Alternatively, would it be better to apply a source term (<\/span>DEFINE_SOURCE<\/code><span class=””>) to the adjacent wall-adjacent cell layer?<\/span><\/p><\/li>\n
    2. <p class=”ds-markdown-paragraph”><span class=””>If I impose a mass flux via UDF on a standard wall, will the pressure force calculated on that face and transmitted to System Coupling automatically account for the momentum loss due to the outflow, or do I need to manually adjust the force vectors in the UDF?<\/span><\/p><\/li>\n
    3. <p class=”ds-markdown-paragraph”><span class=””>Are there any inherent limitations in System Coupling regarding permeable walls defined via UDF (e.g., does the mesh displacement mapping still function correctly when the wall is permeable)?<\/span><\/p><\/li>\n<\/ol>\n

      <p class=”ds-markdown-paragraph”><span class=””>Thank you in advance for your time and insights.<\/span><\/p><p class=”ds-markdown-paragraph”><span class=””>Best regards,<\/span><br><span class=””>Alex<\/span><\/p><\/p>\n","protected":false},"template":"","class_list":["post-459858","topic","type-topic","status-publish","hentry","topic-tag-fluent-ansys-1","topic-tag-2-way-fsi","topic-tag-flow-through-porous-1","topic-tag-porous"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27792"],"_bbp_topic_id":["459858"],"_bbp_subscription":["699141","199"],"_bbp_author_ip":["216.183.237.39"],"_bbp_last_reply_id":["459864"],"_bbp_last_active_id":["459864"],"_bbp_last_active_time":["2026-06-16 14:45:58"],"_bbp_reply_count":["2"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["2"],"_bbp_engagement":["699141","199"],"_btv_view_count":["61"],"_bbp_topic_status":["unanswered"],"_bbp_notification_enabled":["699141"]},"test":"alexandern-zhaofoxmail-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/459858","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\/459858\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=459858"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}