I am curious if anyone had literature references or knowledge on how to apply the Crank-Nicolson (with approximate factorization) to the $$ \nabla \cdot (\nu (\nabla \mathbf{u} + \left(\nabla \mathbf{u}\right)^{T})) $$
What I am unsure about is how to handle the mixed derivative. Currently I am using Crank-Nicolson for
$$ \nu_{Laminar}\nabla^{2} \mathbf{u} $$
which is straight forward as I can solve it dimension-by-dimension.