Global vorticity shedding is a phenomenon where the boundary layer vorticity on an object is released into the fluid as a free vortex when the object is vanished. "Retracting a wing can be a good approximation to ‘vanishing’ if the retraction is fast enough"- MIT research quote.A towed foil can be ‘vanished’ by rapidly retracting the foil in the span-wise direction. As illustrated above, the boundary layer vorticity on a towed foil reforms into two vortices in the fluid that produce strong forces to be used for maneuverability.
