I have implemented open boundary condition according to Zou and He at

the inlet and at the outlet of my system;

I have imposed a poiseuille velocity profile at the inlet, v.

How can I compute mass flow rates, Qin and Qout?

Hello,

the mass flow rate is the integral (sum) of density times velocity. You could compute it like this:

double mass_flow_x = 0; // mass flow in x-direction

X = 0 // inlet or

// X = X_max // outlet

for(Y = 0; Y < Y_max; ++Y) {

for(Z = 0; Z < Z_max; ++Z) {

mass_flow += density(X, Y, Z) * velocity_x(X, Y, Z)

}

}

By the way, if mass_flow_x at inlet and outlet are not the same, the total mass in the system will change.

Timm