Fluent offers geometry macros to get the coordinates of the node. Once you know the node coordinates, use the equation of the circle to get the radius. The code below shows how you implement it.

face_t f;

Thread *tf = DT_THREAD(dt);

real xnode, ynode, r;

int n;

begin_f_loop(f,tf) /* Loops over all faces in the thread passed in the DEFINE macro argument */

{

f_node_loop(f,tf,n) /* Loops over all nodes in the face */

{

Node *node;

xnode = NODE_X(node); /* calculate x-coordinate of a grid point on wall */

ynode = NODE_Y(node); /* calculate y-coordinate of a grid point on wall */

r = sqrt(pow(xnode,2)+pow(ynode,2)); /* calculate radial coordinate of the grid point on wall */

}

//Enter your equation here which you want to calculate as a function of radius

}

end_f_loop(f,tf);