[Cschwatz]

Hello Fluent Wizards,

I'm trying to simulate a multiphase flow in which one of the phases has a non-Newtonian viscosity. Additionally, this viscosity is a function of that phase volume fraction. I had a read in the Fluent UDF manual, as well as some other posts in this forum to come up with something. In this UDF I'm using C_VOF to define volume fraction, but I'm not using the VOF model in my multiphase simulation (I'm using Euler-Euler). Can I still use this macro, despite not using the VOF model?

So far, this is what the UDF is looking like:

---

#include "udf.h"
#include "sg_mphase.h"

DEFINE_PROPERTY(cell_viscosity,c, t)
{
/*Input parameters for the Quemada rheological model*/
real mu_quem, rrbc, k_inf, k0, shear_crit, q, mu_p, exponent, stress,
stress_div, sum_s_crit, sum_s_bracket, sum_b_bracket, e;

Thread *t_rbc = THREAD_SUB_THREAD(t, 1); /* Defining the solid phase*/

rrbc = C_VOF(c, t_rbc);
mu_p = 1020.0;
e = 2.71828;
exponent = -6.0 * rrbc;
sum_s_crit = rrbc + 0.05;
k_inf = 1.0;
k0 = (5.0*pow(rrbc, 0.7)*pow(e, exponent)) + 1.9;
shear_crit = 1.65*pow(sum_s_crit, -0.3);
q = 0.5;
stress = C_STRAIN_RATE_MAG(c, t);
stress_div = stress / shear_crit;
sum_s_bracket = k_inf + ((k0 - k_inf) / (1.0 + pow(stress_div, q)));
sum_b_bracket = 1.0 - (0.5*rrbc*sum_s_bracket);

mu_quem = mu_p * pow(sum_b_bracket, -2.0);

return mu_quem;

}

-----

When I build this UDF in fluent, no errors appear in the console. However, when I try to initialize my simulation the following error appears:

================================================== ============================

Node 0: Process 10896: Received signal SIGSEGV.

================================================== ============================
MPI Application rank 0 exited before MPI_Finalize() with status 2
The fl process could not be started.

What could be causing it?

https://imgur.com/a/nvGNwPw

PS: I've attached a link to an image of the equation used to write the UDF, so it makes easier to follow how I tried to write it in #C.

[AlexanderZ]

try this

#include "udf.h"
#include "sg_mphase.h"

DEFINE_PROPERTY(cell_viscosity,c, t)
{
/*Input parameters for the Quemada rheological model*/
real mu_quem, rrbc, k_inf, k0, shear_crit, q, mu_p, exponent, stress,
stress_div, sum_s_crit, sum_s_bracket, sum_b_bracket, e;
Thread *t_rbc = THREAD_SUB_THREAD(t, 1); /* Defining the solid phase*/

rrbc = C_VOF(c, t_rbc);

return 1e7;

}

best regards

[Cschwatz]

Hello Alexander,

Thanks for the reply! Even though I compiled the code as you have written, it still gave me the same error outcome. By the way, why did you erase the viscosity calculation and asked the code to return a constant value? I think I'm missing something here.

Thanks again!