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3D UDF Paraboilc Velocity Profile with max velocity

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Old   January 4, 2011, 15:35
Default 3D UDF Paraboilc Velocity Profile with max velocity
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John Gosselin
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Hello,

I am simulating the air flow over a 3D building in a wind domain using a paraboilc velocity inlet profile.

I have this UDF but i would like have a max velocity in my UDF, exemple 5 m/s

// UDF code for 3D parabolic Velocity Profile //

#include "udf.h"

DEFINE_PROFILE(inlet_x_velocity, thread, position)

{

real x[ND_ND];

real z; // Vertical Distance

face_t f;

begin_f_loop(f, thread)

{

F_CENTROID(x,f,thread);

z = x[2];

F_PROFILE(f, thread, position) = 24.9 *pow(z,0.27);

}

end_f_loop(f, thread)

}

Thank you
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Old   January 4, 2011, 22:45
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If you just want to limit the velocity, you could look at the lesser of two values: your function, and 5.0. Like this:
Code:
#include "udf.h"

DEFINE_PROFILE(inlet_x_velocity, thread, position)
{
	real x[ND_ND];
	real z; // Vertical Distance
	face_t f;
	begin_f_loop(f, thread)
	{
		F_CENTROID(x,f,thread);
		z = x[2];
		F_PROFILE(f, thread, position) = MIN(24.9 *pow(z,0.27),5.0);
	}
	end_f_loop(f, thread)
}
If the MIN function is giving you trouble (can't remember if Fluent's interpreter has it built-in), you can get the same functionality with:
Code:
#include "udf.h"

DEFINE_PROFILE(inlet_x_velocity, thread, position)
{
	real x[ND_ND];
	real z; // Vertical Distance
	face_t f;
	begin_f_loop(f, thread)
	{
		F_CENTROID(x,f,thread);
		z = x[2];
		F_PROFILE(f, thread, position) = 24.9 *pow(z,0.27);
		if ((24.9 *pow(z,0.27))>5.)
		{
			F_PROFILE(f, thread, position) = 5.0;
		}
	}
	end_f_loop(f, thread)
}
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