{"id":367254,"date":"2024-05-17T06:40:58","date_gmt":"2024-05-17T06:40:58","guid":{"rendered":"\/forum\/forums\/topic\/udf-error-4\/"},"modified":"2024-05-17T06:40:58","modified_gmt":"2024-05-17T06:40:58","slug":"udf-error-4","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/udf-error-4\/","title":{"rendered":"UDF Error"},"content":{"rendered":"

I have attached the UDF at the end. I am trying to use the heat flux to update the mass flow rate at different x values on the inlet surface. I keep getting errors and the temp distribution is weird. On some faces it make sense and others its completely wrong<\/span><\/p>\n

Temp of face 391: -nan(ind) K<\/span><\/p>\n

Heat flux on face 392: -4.41347e+07 W\/m^2<\/span><\/p>\n

Temp of face 392: -nan(ind) K<\/span><\/p>\n

Heat flux on face 393: -2.6595e+06 W\/m^2<\/span><\/p>\n

Temp of face 393: 99.0877 K<\/span><\/p>\n

Heat flux on face 408: 6.20341e+06 W\/m^2<\/span><\/p>\n

Temp of face 408: 1249.73 K<\/span><\/p>\n

Heat flux on face 409: 4.17052e+06 W\/m^2<\/span><\/p>\n

Temp of face 409: 921.292 K<\/span><\/p>\n

Heat flux on face 410: 3.9361e+06 W\/m^2<\/span><\/p>\n

Temp of face 410: 900.957 K<\/span><\/p>\n

pdf_initial_enthalpy: failed to converge for T = -nan(ind), fmean = 0.7, fvar = 0, error = -nan(ind)<\/span><\/p>\n

pdf_initial_enthalpy: failed to converge for T = -nan(ind), fmean = 0.7, fvar = 0, error = -nan(ind)<\/span><\/p>\n

pdf_initial_enthalpy: failed to converge for T = -nan(ind), fmean = 0.7, fvar = 0, error = -nan(ind)<\/span><\/p>\n

 <\/p>\n

#include “udf.h”<\/span><\/div>\n
#include <math.h><\/span><\/div>\n
#define rho 754 \/\/kg\/m^3<\/span><\/div>\n
#define Hg 2033631 \/\/J\/Kg<\/span><\/div>\n
#define Hf -310000 \/\/J\/Kg<\/span><\/div>\n
#define T_ref 298 \/\/T<\/span><\/div>\n
#define A 0.01104 \/\/m\/s<\/span><\/div>\n
#define Cp 1500 \/\/J\/(Kg*K)<\/span><\/div>\n
#define E 20557.188 \/\/J\/mol<\/span><\/div>\n
#define R_u 8.314 \/\/J(m*K)<\/span><\/div>\n
#define D_p 0.04064 \/\/port diameter (m)<\/span><\/div>\n
#define L 0.43815 \/\/Length (m)<\/span><\/div>\n
#define alpha .1<\/span><\/div>\n
DEFINE_PROFILE(surface_temperature_profile, t, position)<\/span><\/div>\n
{<\/span><\/div>\n
    face_t f;<\/span><\/div>\n
    real Ts, heat_flux, heat, a_face, Hv, r, Ts_old, Ts_new_prime, Ts_new, error, Area[ND_ND];<\/span><\/div>\n
    int iter;<\/span><\/div>\n
    begin_f_loop(f, t)<\/span><\/div>\n
    {<\/span><\/div>\n
        if (THREAD_ID(t) == 8)  \/\/ Adjust the surface thread ID as per your case<\/span><\/div>\n
        {<\/span><\/div>\n
            Ts = F_T(f, t);  \/\/ Current temperature at the face<\/span><\/div>\n
   <\/span><\/div>\n
            heat = BOUNDARY_HEAT_FLUX(f, t);  \/\/ Calculating the heat flux at face f in watts<\/span><\/div>\n
            F_AREA(Area, f, t);<\/span><\/div>\n
            a_face = NV_MAG(Area);<\/span><\/div>\n
            heat_flux = heat \/ a_face; \/\/ Heat flux in w\/m^2<\/span><\/div>\n
            printf(“Heat flux on face %d: %g W\/m^2\\n”, f, heat_flux);<\/span><\/div>\n
 <\/div>\n
            \/\/ Iterative calculation for new surface temperature<\/span><\/div>\n
            Ts_old = Ts;<\/span><\/div>\n
            iter = 0;<\/span><\/div>\n
            error = 1;<\/span><\/div>\n
            while (error > 1e-6 && iter < 100)<\/span><\/div>\n
            {<\/span><\/div>\n
                Hv = Hg – Hf + Cp * (Ts_old – T_ref);  \/\/ Calculation heat of formation<\/span><\/div>\n
                r = (fabs(heat_flux)) \/ (Hv * rho);  \/\/ Regression rate<\/span><\/div>\n
                Ts_new = E \/ (R_u * (log(A) – log(r)));  \/\/ New surface temperature<\/span><\/div>\n
                error = fabs(Ts_new – Ts_old);  \/\/ Error calculation<\/span><\/div>\n
                Ts_old = Ts_new;  \/\/ Update Ts_old for next iteration<\/span><\/div>\n
                iter++;  \/\/ Increment iteration count<\/span><\/div>\n
 <\/div>\n
            }<\/span><\/div>\n
    Ts_new_prime = Ts+(alpha*(Ts_new-Ts));<\/span><\/div>\n
    printf(“Temp of face %d: %g K\\n”, f, Ts_new_prime);<\/span><\/div>\n
            F_PROFILE(f, t, position) = Ts_new_prime;  \/\/ Update the face temperature profile<\/span><\/div>\n
        }<\/span><\/div>\n
    }<\/span><\/div>\n
    end_f_loop(f, t)<\/span><\/div>\n
}<\/span><\/div>\n
DEFINE_PROFILE(mass_flow_rate_profile, t, position)<\/span><\/div>\n
{<\/span><\/div>\n
    face_t f;<\/span><\/div>\n
    real heat_flux, heat, a_face, Hv, r, m_dot, Ts, Area[ND_ND];<\/span><\/div>\n
    begin_f_loop(f, t)<\/span><\/div>\n
    {<\/span><\/div>\n
        if (THREAD_ID(t) == 8)  \/\/ Adjust the inlet thread ID as per your case<\/span><\/div>\n
        {<\/span><\/div>\n
            Ts = F_T(f, t);  \/\/ Get the current temperature at the face<\/span><\/div>\n
            heat = BOUNDARY_HEAT_FLUX(f, t);  \/\/ Calculating the heat flux at face f<\/span><\/div>\n
            F_AREA(Area, f, t);<\/span><\/div>\n
            a_face = NV_MAG(Area);<\/span><\/div>\n
            heat_flux = heat \/ a_face;<\/span><\/div>\n
            Hv = Hg – Hf + Cp * (Ts – T_ref);  \/\/ Adjusted Hv calculation with temperature dependency<\/span><\/div>\n
            r = (fabs(heat_flux)) \/ (Hv * rho);  \/\/ Regression rate calculation<\/span><\/div>\n
            m_dot = rho * r * a_face;  \/\/ Mass flow rate calculation<\/span><\/div>\n
    printf(“m_dot fuel %d: %g kg\/s\\n”, f, m_dot);<\/span><\/div>\n
            F_PROFILE(f, t, position) = m_dot;  \/\/ Set the profile for the mass flow rate<\/span><\/div>\n
        }<\/span><\/div>\n
    }<\/span><\/div>\n
    end_f_loop(f, t)<\/span><\/div>\n
}<\/span><\/div>\n

 <\/p>\n","protected":false},"template":"","class_list":["post-367254","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t