Cartesian streamfunction
= Cartesian streamfunction
{title2=$u=\psi_y,\ v=-\psi_x$}
For a two-dimensional <incompressible flow>, a Cartesian streamfunction $\psi$ defines $u=\partial_y\psi$ and $v=-\partial_x\psi$. The continuity equation $u_x+v_y=0$ then holds identically.