The Kármán vortex street is a repeating pattern of alternating vortices shed by a bluff body in a viscous flow. This simulation uses a Lattice Boltzmann Method (LBM) on a D2Q9 grid — 9 velocity directions per cell — to solve the Navier-Stokes equations at the mesoscopic scale. Vortex shedding frequency obeys the Strouhal number: St = fD/U ≈ 0.2 for a cylinder at moderate Reynolds numbers.
Drag the Reynolds number slider: below Re ≈ 40 you see steady attached flow; above Re ≈ 40 vortex shedding begins; above Re ≈ 200 the wake becomes irregular. Click anywhere to add an obstacle — try a square or tilted rectangle. Toggle colour maps between velocity magnitude, vorticity (curl of velocity) and pressure to reveal different aspects of the flow.
In 1940, the Tacoma Narrows Bridge resonated with vortex shedding and collapsed in a 64 km/h wind — a now-iconic example of aeroelastic flutter. Engineers now design bridge decks with aerodynamic cross-sections to suppress shedding. The same phenomenon makes phone wires sing and causes chimneys to oscillate — always a structural concern in wind-exposed design.