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UDF velocity inlet. Different values (compile - Fluent)

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Old   July 13, 2018, 18:02
Default UDF velocity inlet. Different values (compile - Fluent)
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Join Date: May 2018
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Hi all,

I am trying to make a UDF file for the inlet velocity of my flow. The flow needs to follow a stepped function:

0 to 0.5 m/s - 0 to 1 second
constant 0.5 m/s - 1 to 2 second
0.5 - 1 m/s - 2 to 3 seconds,

and so on.

Looking tutorials around I made this UDF:

#include "udf.h"

DEFINE_PROFILE(Vinlet, t, i)
real velocity,ct,m;
int NN;
int N=1;
real tstop[7] = {0,1,2,3,4,5,6};
real Vstop[4] = {0,0.2,0.4,0.6};

face_t f;

if (N % 2 != 0)
NN = N*0.5+0.5;
m = (Vstop[NN]-Vstop[NN-1])/(tstop[N+1]-tstop[N]);
velocity = Vstop[NN-1] + m*(ct-tstop[N-1]);
if (N == 2)
velocity = Vstop[1];
} else {
velocity = Vstop[NN];

if (ct <= tstop[N]+0.001 && ct >= tstop[N]-0.001)
N = N+1;

F_PROFILE(f,t,i) = velocity;
I compile it on an on-line compiler and the velocity follows correctly a stepped function. The problem is that when I try this UDF on FLuent, the velocity increases linearly with time, showing a completely different behaviour.

Anyone knows what could be the reason?

thank you,
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fluent - udf, udf

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