Small perturbations in the velocity field are totally fine even if they are not divergence-free. Most fluid dynamics codes used a discrete Poison equation to en

Small perturbations in the velocity field are totally fine even if they are not divergence-free. Most fluid dynamics codes used a discrete Poison equation to enforce the conservation of mass (i.e. divergence-free velocity field). Here is some background: https://en.wikipedia.org/wiki/Discrete_Poisson_equation#Applications https://en.wikipedia.org/wiki/Discrete_Poisson_equation#Appl...