The Navier-Stokes equations govern viscous fluid flow: ρ(∂u/∂t + u·∇u) = −∇p + μ∇²u. Past a cylinder, flow bifurcates at Re≈40 into the Kármán vortex street — alternating vortices shed periodically. Strouhal number St=fd/U≈0.21 relates shedding frequency, diameter, velocity. This simulation uses the Lattice-Boltzmann method (D2Q9), a mesoscopic approach linking kinetic theory to NS.