Airborne wind energy systems gather energy from the wind using a kite (rigid or soft wing) that pulls on a cable. The cable is connected to the ground and unwinds from a drum, that drives a generator. When the pulling phase ends, the wing comes back, to rewind the cable, and the cycle starts again. This picture shows the vorticity in the wake of such a wing flying a four-loop trajectory. Here it starts the second loop. Flying this trajectory creates turbulence bundles in the wake. Studying the wake is important to understand the interaction with other energy gathering devices.