{"id":436101,"date":"2025-07-04T13:44:28","date_gmt":"2025-07-04T13:44:28","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/uds_flux-incorrectly-computing-advective-sink-term\/"},"modified":"2025-07-04T13:44:28","modified_gmt":"2025-07-04T13:44:28","slug":"uds_flux-incorrectly-computing-advective-sink-term","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/uds_flux-incorrectly-computing-advective-sink-term\/","title":{"rendered":"UDS_FLUX incorrectly computing advective sink term"},"content":{"rendered":"

<p>Hello all,<br><br>I am trying to implement a custom advection-like term that occurs at a gas-liquid interface using User-Defined Scalara functions. See equation (1) <br><br><br>To accomplish this term I am manipulating the DEFINE_UDS_FLUX term. See image below :<br><br>To implement this term using DEFINE_UDS_FLUX, the volume fraction gradient is obtained from a specific adjustment function where it is read by the DEFINE_UDS_FLUX. To make this term a flux, I linearly interpolate the volume fraction gradient values at neighboring cells to get a face value. See code below: <\/p><div><div>DEFINE_UDS_FLUX(VolumFracGrad_Sink, f, t, i)<\/div><div>{<\/div><div>    cell_t c0, c1 = -1;<\/div><div>    Thread *t0, *t1 = NULL;<\/div><div>    real NV_VEC(A), flux = 0.0;<\/div><div> <\/div><div>    \/\/ Cell pointers<\/div><div>    c0 = F_C0(f, t);<\/div><div>    t0 = F_C0_THREAD(f, t);<\/div><div>    c1 = F_C1(f, t);<\/div><div>    t1 = F_C1_THREAD(f, t);<\/div><br><div>    real grad_alpha[3];<\/div><br><div>    \/\/ Compute face area vector<\/div><div>    F_AREA(A, f, t);<\/div><br><div>    if (BOUNDARY_FACE_THREAD_P(t))<\/div><div>     {<\/div><div>            flux = 0;<\/div><div>     }<\/div><div>    else<\/div><div>    {<\/div><br><div>      \/\/ ——————————-<\/div><div>    \/\/ 5. Gradient of alpha<\/div><div>    \/\/ ——————————-<\/div><div>    grad_alpha[0] =(C_UDMI(c0, t0, 0)+C_UDMI(c1, t1, 0))*0.5;<\/div><div>    grad_alpha[1] =(C_UDMI(c0, t0, 1)+C_UDMI(c1, t1, 1))*0.5;<\/div><div>    grad_alpha[2] =(C_UDMI(c0, t0, 2)+C_UDMI(c1, t1, 2))*0.5;<\/div><br><br><div>    flux =  <span style=”font-size: 14pt;”>-NV_DOT(grad_alpha,A);<\/span><\/div><br><br><div>    }<\/div><div> <\/div><br><div>    return flux;<\/div><div>}<br><br>However, when I run this code using a volume of fluid approach with a sharp interface and a highly refined domain, I obtain this result.<\/div><\/div><p><br><br><br>Has anyone came across a similar problem? I’d expect a uniform result, not a skewed result. If I just take the x-direction gradient with no face area attachted, I get this result :<br><br><br>It is very strange because If I plot the volume fraction gradient obtained in the defined adjust function (which is saved as C_UDMI(c,t,0 to 2) this is the results: <br><br><br>However, it does seem that ansys is predicting a y-direction volume fraction gradient.. could this be the issue? <br><br><br><br><\/p><\/p>\n","protected":false},"template":"","class_list":["post-436101","topic","type-topic","status-publish","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27792"],"_bbp_topic_id":["436101"],"_bbp_subscription":["12734","62368"],"_bbp_author_ip":["217.147.184.241"],"_bbp_last_reply_id":["436928"],"_bbp_last_active_id":["436928"],"_bbp_last_active_time":["2025-07-15 16:45:51"],"_bbp_reply_count":["1"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["2"],"_bbp_engagement":["12734","62368"],"_btv_view_count":["179"],"_bbp_topic_status":["unanswered"]},"test":"anthony_bowersstudent-uml-edu"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/436101","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\/436101\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=436101"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}