Caption list:

Movie 1: The second mode is associated with stronger dynamics
in the gap and intermittent shedding of gap vortices, as well as overshoot of the gap shear
layers further into the near-wake, and wider gap and wake widths. The second mode starts around $tU_{0} /D = 379$.

Movie 2: Secondary gap vortices are created through interaction between the overshooting gap shear layer (the lower one) and the near-wake.

Movie 3: recirculating fluid entrained by strong gap vortices will sometimes impinge on the shear layer on the same side of the gap at which it was entrained. This way, the fluid enhances the roll-up process, and contributes to repeated shedding on one side of the gap. Lower-momentum entrained fluid is mostly swallowed by the gap vortex forming on the opposite side.