# Starting vortex The starting vortex is the swirl a wing sheds the instant it begins to move. At rest there is no [[Circulation_(physics)|circulation]] anywhere; as the wing accelerates, flow tries to whip around the sharp trailing edge, [[Viscosity]] refuses, and the attempt rolls off as a discrete [[Vortex]] left behind in the air. What it leaves behind on the wing is an equal and opposite bound circulation — and that is the circulation the [[Kutta–Joukowski_theorem]] turns into lift. ## Lift's receipt [[Kelvin's_circulation_theorem]] requires that a large loop enclosing both wing and shed vortex still have zero total circulation, exactly as before the wing moved. So the wing did not create rotation; it separated rotation of opposite signs and abandoned one half. Everything downstream follows: the shed vortex is the fourth leg of the [[Horseshoe_vortex]], and the trailing legs are the [[Wingtip_vortices]] that persist behind the aircraft. Change angle of attack in flight and a new starting vortex is shed each time, which is why unsteady [[Aerospace_engineering|aerodynamics]] is harder than the steady case. ## Watchable It is one of the few pieces of theoretical [[Fluid_dynamics]] you can see directly. Draw an aerofoil through a shallow tray of [[Water]] dusted with powder and the vortex peels off the trailing edge and sits there, slowly decaying by [[Diffusion]], while the foil moves away with its bound circulation. Prandtl filmed exactly this a century ago. The same shedding starts every propeller, every [[WT!Energy_Center_of_Excellence|turbine]] blade, and every fish tail-beat. **Microsim brief (next pass):** Aerofoil that accelerates from rest on a click; the starting vortex peels off the trailing edge and stays put while bound circulation appears as a rotating overlay on the foil. **On the spine:** [[Circulation_(physics)]] · [[Kutta–Joukowski_theorem]] · [[Kelvin's_circulation_theorem]] · [[Wingtip_vortices]] · [[WT!Thury_Hydrodynamics_Compendium]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Starting_vortex) : [Wikitube](https://en.wikitube.io/wiki/Starting_vortex) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_WT!Thury_Hydrodynamics_Compendium]], [[PORTAL_Aviation]], [[PORTAL_Physics]]. --- *Fluid seed wave · 2026-09-10 · seed register · microsim layer pending.*