[aar007]

Hi, I am trying to model a UDF for my wind tunnel inlet using power law.
1; when I try computing my inlet conditions from in reference value I get *nan* in velocity section
(#include "udf.h"

#define P 1./7. //power law n value 7//
#define uref 1.32 // m higeht of inlet//


DEFINE_PROFILE(inlet_x_velocity, thread, position)
{
real x[ND_ND]; /* this will hold the position vector */
real z;
face_t f;

begin_f_loop(f, thread)
{
F_CENTROID(x,f,thread);
z = x[2];
F_PROFILE(f, thread, position) = 40*pow(z/uref,P);
}
end_f_loop(f, thread)
}

2; I get the same issue and error when I try using the function expression.

uref [m s^-1] * (z / z_ref [m]) ** alpha3.my inlet is at x=-1 using magnitude and direction under velocity specification method

[vinerm]

The UDF is alright and you can use it. However, this cannot be used for initialization. DEFINE_PROFILE is not executed before initialization. You have to initialize by providing some value for the velocity.

[ved prakash]

Hi, have you found the solution?? I am also trying to use this expression. Please help me out.

[AlexanderZ]

solution is written by vinerm one line above