[yonpanman]

Hello everyone!

I am trying to create an increase of velocity in a flow over a wing in order to simulate a gust wind. The idea is to apply a momentum source in a region upstream of the wing and let the perturbation flow downstream through convection. I found this

https://www.sharcnet.ca/Software/Flu...ug/node309.htm

When I use the UDF below I get strange changes in the velocity field where smaller cells gets a much higher velocity than larger. I suppose it sort of makes sense the source term divides by the volume and I fear I have misunderstood something.

If anyone have experience with this kind of implementation, or has another suggestion of achieving a similar result, it would be of great help. Below you find the udf and a picture of the flowfield.

#include "udf.h"

real A[ND_ND]; /* Declared as global variables*/
real area;

DEFINE_ON_DEMAND(face_area)
{
Domain *d = Get_Domain(1);
Thread *ft;
face_t f;

thread_loop_f(ft,d) /* Finding the area of the cell face with a define on demand macro. Found this in another thread here on CFD-online */
{
begin_f_loop(f,ft)
{
real NV_VEC(A);
F_AREA(A,f,ft);
area = NV_MAG(A);
}
end_f_loop(f,ft)
}

}

DEFINE_SOURCE(source_still_in_sharp_smooth, c,t,dS,eqn)
{

real x[ND_ND];
C_CENTROID(x,c,t)
real x_0 = x[0];
real pi = 3.14159265359;

real Wg = 10; /* amplitude gust */

real start_g = -5; /* start gust source region */
real length_g = 1; /* length gust source region */
real end_g = (start_g + length_g); /* end gust source region */

real real_time = CURRENT_TIME;
real start_time_gust = 0.01; /* start time gust */
real end_time_gust = 0.51; /* end time gust */
real gust_time = (real_time - start_time_gust);
real gust;


if(0 <= gust_time && gust_time <= end_time_gust)
{
if(start_g <= x_0 && x_0 <= end_g)
{
gust = (C_U(c,t) + 5) * C_R(c,t) * area / C_VOLUME(c,t); /* flux through cell, 5 [m/s] is the perturbation */
}
else
{
gust = 0.0;
}
}
else
{
gust = 0.0;
}


real source = gust; /* whetever your source is */
dS[eqn] = C_R(c,t) * area / C_VOLUME(c,t); /* derivative source term */

return source;

}