UDF for critical strain rate to extinction
 

Hello everyone

I am using partially premixed combustion model with propane. My problem arises when I try to define critical strain rate to extinction g_cr=U^2/alpha, where U is laminar burning velocity and alpha is thermal diffusivity. Fluent compiles or interprets UDF without any problem (I tried both options). My "headache" starts when I hook UDF. Fluent gives following error:

Error:

FLUENT received fatal signal (ACCESS_VIOLATION) 1. Note exact events leading to error. 2. Save case/data under new name. 3. Exit program and restart to continue. 4. Report error to your distributor. Error Object: ()

Interrupting... Done.

This is a very simple UDF:

/************************************************** ********* strain1.c UDF for critical strain rate to extinction ************************************************** *********/

#include "udf.h"

#include "sg_mem.h"

DEFINE_PROPERTY(critical_strain_rate,c,t) { real S_ext; real alpha_c; real u_lam = C_LAM_FLAME_SPEED(c,t); real k_c = C_K_L(c,t); real rho_c = C_R(c,t); real cp_c = C_CP(c,t); alpha_c = k_c/(rho_c*cp_c); S_ext = (u_lam*u_lam)/alpha_c;

return S_ext; }

I will appreciate for any hints and tips, how I could solve this problem.

Thanks, Birute

Hi,

This (too) late, this is not a fix. It's rather a conceptual matter.
You need the "unburnt" thermal diffusivity for the expression of the critical rate of strain, that is you need to use the unburnt mixture properties. I wrote a UDF for that but I use mean mixture fraction polynomial curve fits to compute the unburnt thermal diffusivity (you can get these from Fluent). However, for some reason, it's not giving me what I expect. Did you manage to figure out how to do this eventually?

Ace