Vortex Ring Wake of a Flapping Bird Wing

Every downstroke of a bird's wing sheds a discrete ring of circulation into the air behind it, the way a smoke ring is puffed from a chimney — the vortex-ring wake model that replaced the naive "two continuous trailing vortices" picture once high-speed wake visualisation of real birds became possible. This simulator flaps a bird's wings through a controllable stroke cycle and sheds a genuine chain of vortex rings, one per wingbeat, whose spacing, size and strength are all driven by the same aerodynamic parameters — airspeed, wingbeat frequency, stroke amplitude, and bound circulation — that determine the bird's lift and the wake's Strouhal number in real flight.