{"id":30599,"date":"2018-09-26T02:38:36","date_gmt":"2018-09-26T02:38:36","guid":{"rendered":"\/forum\/forums\/topic\/udf-for-atmospheric-boundary-layer-abl\/"},"modified":"2018-09-26T02:38:36","modified_gmt":"2018-09-26T02:38:36","slug":"udf-for-atmospheric-boundary-layer-abl","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/udf-for-atmospheric-boundary-layer-abl\/","title":{"rendered":"UDF for Atmospheric Boundary Layer (ABL)"},"content":{"rendered":"

Hello,<\/p>\n

<\/p>\n

I have been trying to simulate a homogenous ABL profile based on Richards and Hoxey’s 1993 approach<\/a> using FLUENT software, which requires a UDF at the inlet. I succeeded in  creating the velocity profile using the log law<\/p>\n

<\/p>\n

Uref= u (log(href\/z0)\/log(h\/z0)) [shown below in code]<\/p>\n

<\/p>\n

Uref<\/strong>: reference velocity at refernce height (<\/strong>href)<\/strong>, u<\/strong>: velocity at h (height), and z0<\/strong>: aerodynamic roughness height.<\/p>\n

<\/p>\n

The result was successful as shown:<\/p>\n

<\/p>\n

\"\"<\/p>\n

<\/p>\n

However, a homogenous turbulence kinetic energy (TKE) and dissipation rate (TDR) were not generated despite the inserted constant values (calculated from the mentioned apprach relative to friction velocity, u*) in the inlet display window as shown (the values were changed from 1 and 1 to differnt numbers of course).  The results changed due to the ground roughness (may be) that might be another possible influence (UDF?).<\/p>\n

<\/p>\n

\"\"<\/p>\n

<\/p>\n

So I tried making a UDF code for both TKE and TDR as well to keep them constant based on the codes below, but it didn’t work as well, the TKE gave high values at the top and minimum (zero) at the bottom:<\/p>\n

<\/p>\n

#include “udf.h”<\/p>\n

 #define z0 0.0000824          \/* constants *\/
 #define z1 0.4
 #define uref 14.7
 #define CMU 0.09
 #define VKC 0.41<\/p>\n

 \/* profile for x-velocity *\/<\/p>\n

 DEFINE_PROFILE(log_velocity,thread,index)
 {
   real y[ND_ND];
   real z2;
   face_t f;<\/p>\n

   begin_f_loop(f,thread)
   {
        F_CENTROID(y,f,thread);
    z2 = y[1];
    F_PROFILE(f,thread,index) = uref*log(z2\/z0)\/log(z1\/z0);
    }
 end_f_loop(f,thread)
   }<\/p>\n

 \/* profile for kinetic energy *\/
 
 DEFINE_PROFILE(k_profile,thread,index)
 {
    real y[ND_ND], lgr, ustr;
    real k;
    face_t f;<\/p>\n

    lgr = log((z1+z0)\/z0);
    ustr = (uref*VKC)\/lgr;
       <\/p>\n

    begin_f_loop(f,thread)
      {
         F_CENTROID(y,f,thread);<\/p>\n

<\/p>\n

         k = pow(ustr,2.)\/sqrt(CMU);
         F_PROFILE(f,thread,index) = k;
          
        }
      end_f_loop(f,thread)
   }<\/p>\n

\/* profile for dissipation rate *\/
 
 DEFINE_PROFILE(dissip_profile,thread,index)
 {
    real y[ND_ND], lgr, ustr;
    real eps;
    face_t f;<\/p>\n

    lgr = log((z1+z0)\/z0);
    ustr = (uref*VKC)\/lgr;
    <\/p>\n

    begin_f_loop(f,thread)
      {
         F_CENTROID(y,f,thread);<\/p>\n

<\/p>\n

         eps = pow(ustr,3.)\/(VKC*(z1+z0));
         F_PROFILE(f,thread,index) = eps;<\/p>\n

        }
      end_f_loop(f,thread)
 }<\/p>\n

<\/p>\n

 <\/p>\n

<\/p>\n

what should I do?<\/p>\n

<\/p>\n

Kindly notice that, I’m not good coder, in fact I don’t know how to write codes, my efforts were done to try understand them, so this code is  a beginner trial. My question is How?, Am I missing something?<\/p>\n

<\/p>\n

and yes, I read the manual.<\/p>\n

<\/p>\n

 <\/p>\n

<\/p>\n

Thank you for support<\/p>\n

<\/p>\n

Ahmad<\/p>\n","protected":false},"template":"","class_list":["post-30599","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_old_topic_id":["2771"],"_bbp_old_topic_author_name_id":["Anonymous"],"_bbp_old_is_topic_anonymous_id":["false"],"_bbp_old_closed_status_id":["publish"],"_bbp_author_ip":[null],"_bbp_old_sticky_status_id":["normal"],"_bbp_likes_count":["0","0","0","0","0"],"_btv_view_count":["2200"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["30599"],"_bbp_forum_id":["27792"],"_bbp_engagement":["25","199","4948","22555","158541","162684","175441"],"_bbp_voice_count":["7"],"_bbp_reply_count":["23"],"_bbp_last_reply_id":["112668"],"_bbp_last_active_id":["112668"],"_bbp_last_active_time":["2020-04-27 11:38:41"]},"test":"ahmadzaki"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/30599","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\/30599\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=30599"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}