Reply To: Unexpected Downward Trend in Turb. Intensity Using Variable k and ε in Fluent

[anupamkrishnan91]

Hi, Thank you for the reply. 
#UDF Starts from the next line#

#include "udf.h"

#include "math.h"

#include "stdlib.h"

 

// Define constants

#define C_MU 0.09

#define LENGTH_SCALE 0.07 /* Approximate length scale as 7% of characteristic length */

#define VELOCITY 1.46 /* Mean velocity (m/s) */

#define MIN_TI 0.44 /* Minimum turbulence intensity: 44% */

#define MAX_TI 0.60 /* Maximum turbulence intensity: 60% */

 

// Function to set time-dependent turbulent kinetic energy (k)

DEFINE_PROFILE(variable_k, thread, position)

{

    real time = CURRENT_TIME; /* Get current simulation time */

    real I; /* Turbulence intensity */

    real k; /* Turbulent kinetic energy */

    face_t f;

 

    /* Predefined turbulence intensity values*/

    real TI_values[15] = {0.44, 0.44, 0.44, 0.48, 0.51, 0.53, 0.56, 0.58, 0.56, 0.55, 0.53, 0.50, 0.49, 0.48, 0.46}; // Values adjusted

 

    int index = (int)(time); /* Convert time to an integer index (0 to 14) */

    if (index > 14) 

    {

        index = 14; /* Cap the index at 14 to keep TI at 46% after 15 seconds */

    }

 

    I = TI_values[index]; /* Assign the corresponding turbulence intensity */

 

    begin_f_loop(f, thread)

    {

        /* Compute turbulent kinetic energy (k) based on turbulence intensity (I) */

        k = 1.5 * pow(I * VELOCITY, 2); /* k = 3/2 * (I * U)^2 */

 

        F_PROFILE(f, thread, position) = k;

    }

    end_f_loop(f, thread)

}

 

// Function to set time-dependent turbulent dissipation rate (ε) based on k

DEFINE_PROFILE(variable_epsilon, thread, position)

{

    real time = CURRENT_TIME; /* Get current simulation time */

    real I; /* Turbulence intensity */

    real k; /* Turbulent kinetic energy */

    real epsilon; /* Turbulent dissipation rate */

    real l = LENGTH_SCALE; /* Turbulence length scale */

    face_t f;

 

    /* Predefined turbulence intensity values */

    real TI_values[15] = {0.44, 0.44, 0.44, 0.48, 0.51, 0.53, 0.56, 0.58, 0.56, 0.55, 0.53, 0.50, 0.49, 0.48, 0.46}; // Values adjusted

 

    int index = (int)(time); /* Convert time to an integer index (0 to 14) */

    if (index > 14) 

    {

        index = 14; /* Cap the index at 14 to keep TI at 46% after 15 seconds */

    }

 

    I = TI_values[index]; /* Assign the corresponding turbulence intensity */

 

    begin_f_loop(f, thread)

    {

        /* Compute turbulent kinetic energy (k) */

        k = 1.5 * pow(I * VELOCITY, 2); /* k = 3/2 * (I * U)^2 */

 

        /* Compute dissipation rate (ε) */

        epsilon = pow(C_MU, 0.75) * pow(k, 1.5) / l;

 

        F_PROFILE(f, thread, position) = epsilon;

    }

    end_f_loop(f, thread)

}

###

This is the UDF that I am using. 

Hope this would define the problem. 
Thanks in advance.