[Quinos]

Hello everyone,

I am trying to write a DEFINE_MASS_TRANSFER UDF for my FLUENT model. The code is attached below. This is a test UDF since it just returns a single value at the moment.

My UDF can be interpreted(via Define -> User-Defined -> Functions -> Interpreted...) without errors, and I can select the specific UDF in my model afterwards, but when I try and run my model, the following errors come up.

What am I doing wrong? Any help would be appreciated; I'm new at this.

Updating solution at time level N... done.
iter continuity x-velocity y-velocity z-velocity energy hydrogen+-ph hydrogen+-ph vf-phase-2 time/iter
chip-exec: simple_diff: wrong return type: void udf function expected
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: #f

// UDF to define a simple mass transfer based on simple diffusion from One to Two

#include "udf.h"

DEFINE_MASS_TRANSFER(simple_diff,cell,thread,from_index,from_species_index,to_index,to_species_index)
{
	real m_ot, D_ot;
	real est_area, flux_ot;
	Thread *one = 
	THREAD_SUB_THREAD(thread,from_index);
	Thread *two = 
	THREAD_SUB_THREAD(thread,to_index);
	
	//m_ot = 0.;
	//D_ot = 9.31*pow(10,-9);
	//est_area = pow(C_VOLUME(cell,one),2.0/3.0);
	//flux_ot = -D_ot*(C_YI(cell,one,from_species_index)-C_YI(cell,two,to_species_index));
	//m_ot = flux_ot*est_area*1.7*pow(10,-27)*6*pow(10,23)*C_VOLUME(cell,one);
	
	//return (m_ot);
	real X = 5.0;
	
	return(X);
}