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-   -   UDF problem : inlet velocity in cyl. coord. system (https://www.cfd-online.com/Forums/fluent/33972-udf-problem-inlet-velocity-cyl-coord-system.html)

 Jongdae Kim June 15, 2004 11:21

UDF problem : inlet velocity in cyl. coord. system

Computational domain of the (tornado) simulation is defined in the 3-dimensional cylindrical coordinate system.

I'd like to change the uniform inlet velocities (radial, swirl and axial velocities) to the boundary layer type velocities.

Please let me know how to define such velocities using UDF.

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Why boundary layer type?

From the 2-dim. axisymmetry analysis of a tonado, the uniform inlet boundary condition gives more intensive tornadic core than the case of using the boundary layer type inlet velocity condition. Also, when boundary layer type inlet velocity is used, the velocity profiles show similar trend with the experimental data from tornadic chamber test.

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The following is the UDF used for the inlet velocity profiles for a 2-dim axisym. analysis.

/************************************************** **/

/* UDF for specifing the inlet */ /* radial & swirl velocity profile */ /* for inlet boundary condtions */

/************************************************** **/

#include "udf.h"

#define ALFA 0.113

#define ZH 0.025

#define VH 0.3

#define VISC 1.7894e-05

#define DEFU 1.00 /* deffuser effect compesstor */

#define S 0.28 /* swirl ratio */

{

real x[ND_ND];

real z;

face_t f;

{

z = x[0];

F_PROFILE(f, thread, position) = (-DEFU*VH)*pow (z/ZH, ALFA);

}

}

/* Profile for swirl-velocity */

{

real x[ND_ND];

real z;

real V;

face_t f;

{

z = x[0];

V = S*2.0*VH;

F_PROFILE(f, thread, position) = (DEFU*V)*pow(z/ZH, ALFA);

}