# Why my UDF return Zero?

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 August 27, 2015, 04:40 Why my UDF return Zero? #1 Member   Siamak Join Date: Jul 2014 Location: Australia Posts: 33 Rep Power: 4 Hello Friends, I am going to calculate the following expression in FLUENT to plot the vorticity in my 2D model. D=(du/dx+dv/dy)^2-4(du/dx*dv/dy-du/dy*dv/dx) I write the following UDF: DEFINE_ON_DEMAND(vorticity) { Domain *domain; cell_t c; Thread *t; domain=Get_Domain(1); thread_loop_c (t,domain) { begin_c_loop (c,t) { C_UDMI(c,t,0) = pow((C_DUDX(c,t)+C_DVDY(c,t)),2)+4*(C_DUDX(c,t)*C_ DVDY(c,t)-C_DUDY(c,t)*C_DVDX(c,t)); } end_c_loop (c,t) } Message("Done!"); } But when I run the execution on demand, it returns zero, that means this code is not working? I change the formula and write C_UDMI(c,t,0) = C_DUDX(c,t) and again it returns zero. Why velocity derivatives are not working? Thank you in advance for your assistance Siamak

 August 27, 2015, 06:16 #2 Senior Member   Bruno Machado Join Date: May 2014 Posts: 258 Rep Power: 5 Add this line before your message and compute manually the values to make sure you are reading them correctly: if((c%10000) == 0) Message("DUDX %f, DVDY %f, DUDY%f, DVDX %f\n", C_DUDX(c,t), C_DVDY(c,t), C_DUDY(c,t), C_DVDX(c,t));

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