I want to write a UDF for parabolic velocity proifles for flow in a 3-Dimensional pipe. Can any one suggest me.

It's just the same as in 2D. Write the equation of the paraboloid which represents your profile.

Suppose your flow is oriented along the z axiz. Center the inlet with the origin of your reference system. Your profile will assume the simple form:

z = a*x^2 + b*y^2 + c

Use the macro F_CENTROID to retrieve the cell centroid coordinates, with a line like the following:

F_CENTROID(x,f,t);

where x is an array of dimension ND_ND, f is the face and t the thread. Then, you can put

x = x[0];

y = x[1];

and use

F_PROFILE(f, t, i) = a*pow(x,2) + b*pow(y,2) + c;

replacing a, b and c with their values.

Hi

ap

ap,

why do you put Hi

at the end of your message?

Just a nice and short way to say "Hello and good work". A smile always helps.

Hi

ap

Hi everyone,

Suppose i am using the velocity at the inlet of the st. pipe is 0.45 m/s. The ID of the tube is 0.0102 m, by using these values i made a UDF for 3D as

#include "udf.h"

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

begin_f_loop(f, thread)

{

F_CENTROID(x,f,thread);

y = x[0];

z = x[1]; F_PROFILE(f,thread,position)=0.45-y*y/(.0051*.0051)*0.45-z*z/(.0051*.0051)*0.45;

} end_f_loop(f, thread) }

when is read the velocity at the inlet of the tube it shows 2400 m/s. there is somthing wrong, can you please suggest me what is wrong here.

If your velocity profile is function of y and z coordinates, these two lines are wrong:

y = x[0];

z = x[1];

The x vector contains in the order x,y,z coordinates. So:

x[0] -> x coordinate

x[1] -> y coordinate

x[2] -> z coordinate

To check the paraboloid equation, just plot it in a softwnare like gnuplot.

Hi

ap