Visualize Karman vortex street formation behind a cylinder, vorticity field, and force coefficient dynamics
When fluid flows past a bluff body (such as a cylinder) at moderate Reynolds numbers (Re ~ 50-300), alternating vortices shed from each side of the body, forming two staggered rows of vortices known as the Karman vortex street. The shedding frequency f follows the Strouhal relation: St = fD/U, where St ~ 0.2 for cylinders. Theodore von Karman (1911) analyzed the stability of such vortex arrangements and showed that the staggered configuration is the only stable arrangement.
For a cylinder, very low Reynolds numbers produce creeping flow with little or no separation; intermediate values produce a steady attached wake; and higher subcritical values lead to periodic vortex shedding. This page is most faithful in that low-to-moderate Reynolds-number regime. It does not attempt to reproduce drag-crisis or fully turbulent high-Re cylinder physics.
Vortex shedding causes periodic forces on structures: bridges (Tacoma Narrows, 1940), chimneys, offshore risers, heat exchanger tubes, and power transmission lines. If the shedding frequency locks onto a structural natural frequency, resonance amplifies vibrations leading to fatigue failure. Engineers use Strouhal number correlations, helical strakes, and damping to mitigate vortex-induced vibration.
Karman vortex streets form in the atmosphere when stable stratified air flows past islands. Satellite imagery shows spectacular vortex streets downwind of Guadalupe Island, the Canary Islands, and Jeju Island. These mesoscale vortices can extend hundreds of kilometers with spacing following the same stability analysis as laboratory-scale vortex streets.
The main field can display vorticity, speed magnitude, or pressure proxy around the cylinder. In vorticity mode, red = counter-clockwise and blue = clockwise. Watch how alternating vortices form behind the cylinder and arrange into a staggered pattern. The force plot shows lift (oscillating) and drag (mean + oscillation). The spectrum marks the measured dominant lift-oscillation peak and the reference Strouhal prediction.
1) Start with 'Vortex Street' preset and observe regular alternating shedding. 2) Switch to 'Attached Pair' and note the mostly steady wake with no periodic shedding. 3) Try 'Higher Re' to see stronger, less regular shedding within this 2D subcritical model. 4) Adjust flow speed and viscosity to change Re. 5) Compare the measured lift-spectrum peak with the reference Strouhal line. 6) Use the color-mode switch to compare vorticity, speed magnitude, and pressure proxy views.