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Old   December 14, 2011, 09:38
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Hi all

about UDF, when do need to use C_P(c,t) and when F_P(c,t), also the other parameters like U_P(c,t) and F_P(c,t) and so on....
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Old   December 16, 2011, 08:42
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C_P(t,c) gives the pressure value in the centroid of the cell.
F_P(t,f) gives the pressure value in the centroid of the face.
I would recommend to read the manual regarding these macros. The face values are not available in the entire domain for all variables!
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Old   December 16, 2011, 09:19
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thanks for the reply, iv actually read already but get confused a bit,
im wondering if the following is correct for calculating pressure at outlet:


DEFINE_EXECUTE_AT_END(network_calculation)
{

FILE *flow_rate,*update,*velocity;


Domain *d;

real force=0.;
real NV_VEC(A);
face_t f;
Thread *t;
d = Get_Domain(1);
t = Lookup_Thread(d,2);

PF = 0.0;
area = 0.0;
force = 0.0;

begin_f_loop(f,t)
{
F_AREA (A,f,t);
force+=F_P(f,t)*NV_MAG(A);
area +=NV_MAG(A);
PF= force/area;
}
end_f_loop(f,t)
}

thank you
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Old   December 16, 2011, 10:07
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It looks ok if the outlet zone id is 2.
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Old   December 17, 2011, 05:37
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thanks for reply,
but the point is, for example when i measure the area in solid work it is a bit different from the area+=NV_MAG(A) computed through this code in fluent,
that is why it makes me feel doubt about how correct the code i use is..
please let me know
thanks so much again...
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Old   December 17, 2011, 10:42
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That's easy: Solid Works or any other CAD software keeps the surface as a parametric object (meaning there is an equation describing the surface), whereas fluent keeps the same surface as a triangular surface (meaning a discrete form). The discrete form will always include a discretization error based on the size of the discretization, so there is no surprise that you get a difference. This difference, between the CAD and CFD software should decrease if you have a finer mesh.
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