[Ionut G]

Hi,

I want to determine the cell wall distance or to get its values from FLUENT Solver.
I need the cell wall distance to compute the yStar, and eventually to calculate the velocity (to use a custom wall function).

I tried to calculate the cell wall distance by identify the wall thread. The code that I used it is written below.
After I did a simulation I compared the values from of "Cell Wall Distance" variable from fluent with the ones that I compute "dist". I attached a the graph comparing the two variables.

1. What I did wrong in my code?
2. It is possible to get the values of the "Cell Wall Distance" from the solver so that I can use them in my udf? Like a macro or something like that?
3. Is this function "C_STORAGE_R(f,t,SV_WALL_YPLUS)" the yStar?

The geometry that I use is a 3D asymetric diffuser (Diffuser 1 from the article "Geometric sensitivity of three-dimensional separated by Erica M. Cherry" http://www.sciencedirect.com/science...42727X08000131).

DEFINE_ADJUST(ystar, d)
{
	d = Get_Domain(1);
	Thread *t_wall;
	Thread *t_adj;
	cell_t c_adj;
	face_t f;
	
	real f_cen[ND_ND], c_cen[ND_ND], dist;
	real k, y_star;
	
// Identify the wall cell thread	
	int wall_id = 11;
	t_wall = Lookup_Thread(d,wall_id);
	
	begin_f_loop(f,t_wall)
	{
// Identify the adjacent cells and thread to the wall
		c_adj = F_C0(f,t_wall);
		t_adj = THREAD_T0(t_wall);
		
// Extract Turbulent Kinetic Energy from solver
		k = C_K(c_adj,t_adj);
		
// Get the face and cell centroid near the wall
		F_CENTROID(f_cen,f,t_wall);
		C_CENTROID(c_cen,c_adj,t_adj);
		
// Compute the distance from the cell of first layer to the face on the wall		
		dist = sqrt(ND_SUM(pow(c_cen[0]-f_cen[0],2),pow(c_cen[1]-f_cen[1],2),pow(c_cen[2]-f_cen[2],2)));
		C_UDMI(c_adj,t_adj,2) = dist;

// Extract yStar
		C_UDMI(c_adj,t_adj,1) = C_STORAGE_R(f,t_wall,SV_WALL_YPLUS);
		
// Compute yStar		
     	y_star = (DENSITY*pow(CMU,(1./4.))*pow(k,(1./2.))*dist)/MU;
     	C_UDMI(c_adj,t_adj,0) = y_star;
     	//printf("dist: %d\n", dist);
	}
	end_f_loop(f,t_wall)
}

Thank you for support.