I know that residual tell about the solution convergence, but how to define them, and understand that definition?

After solving N.S eqautions there is some imbalance. This is what residual are. They are the imbalance left inside cell. It should be very low like 0.0001 .

best regards john

u vcan define in convergence criteria of any commercial code .

Thanks,

And what if the residual is more than 0.0001 (oscillation above)?