Classic Navier-Stokes benchmark: a square cavity with a moving top lid. A vorticity-streamfunction formulation on a staggered grid. Watch secondary recirculation zones appear at high Re.
Vorticity-streamfunction formulation: ω_t + (u·∇)ω = (1/Re)∇²ω, ∇²ψ = −ω, u=∂ψ/∂y, v=−∂ψ/∂x