Calculate the viscous forces on a patch
 

Hello!

I am using foam-extend-3.2.
I want to obtain the forces and moments acting on a spherical particle in the channel flow. The forces and moments will be used to adjust the slip velocity on the particle surface. The forces are calculated by the script below and show to be different from the forces output by the libforces.so.


totalForce
{
type patchExpression;
outputControlMode timeStep;
enabled true;
outputInterval 1;
patches (
sphere_region0
// change to your name or names of patch
);
verbose true;
variables (
"position=0;"
"rho=1;"
"mu=1.0;"
"pressure_forces= rho*p*normal()*area();"
"viscous_forces= -mu*snGrad(U)*area();"
"forces=pressure_forces+viscous_forces;"
);
expression "forces";
accumulations ( sum );
}


Thank you in advance.

Su