Vorticity

$$\frac{\partial \omega}{\partial t} = \nu \nabla^2 \omega - \mathbf{u}\cdot\nabla \omega$$

$$\nabla^2 \psi = -\omega\$$

$$\mathbf{u}=\nabla\times\psi$$

$$\frac{\partial S}{\partial t} = D \nabla^2 S - \mathbf{u}\cdot\nabla S$$