[mmj_blackforce]

Dear members;
i have been trying to add a vertical gust through momentum source udf.
i have succeeded in compiling and running the udf, however there remains a problem which i could not understand as yet.

my main concern is what should be the value of source so as to induce a perturbation of 15m/s as y-gust component. how is the value of source calculated?

Can someone please answer the querry.
my udf is as follows.

# include "udf.h"

DEFINE_SOURCE(gust,cell,thread,dS,eqn)
{
real source=0.0;
real PI=3.14;
real XGS=-7.5; /* X-center of source*/
real YGS=0.0; /* Y-center of source*/
real ZGS=0.0; /* Z-center of source*/
real X= 1.0; /* X, Y, Z dimensions make the source-Volume=1m^3*/
real Y= 1.0;
real Z= 1.0;
real t = CURRENT_TIME;

real centroid[ND_ND];
C_CENTROID(centroid,cell,thread);
real x_loc=centroid[0];
real y_loc=centroid[1];
real z_loc=centroid[2];
if (t>1.0 && t<1.2)
{
if (fabs(x_loc-XGS)<X && fabs(y_loc-YGS)<Y && fabs(z_loc-ZGS)<Z)
{
real rho=C_R(cell,thread);
real vol=C_VOLUME(cell,thread);
source=((rho*(15.0+C_V(cell,thread))/CURRENT_TIMESTEP))/vol; /*15(m/s) is perturbation in Y direction*/
dS[eqn]=0.0;
}
}
else
{
source=0.0;
dS[eqn]=0.0;
}
return source;
}

[mmj_blackforce]

Hi everyone,
Can anyone please explain the relation between velocity and momentum source term equation?