  Kirigami patterned materials have found several applications in recent years
due to their ability to assume complicated shapes and exhibit emergent physical
properties when exposed to external forces. Consisting of an array of cuts in a
thin material, fabrication of these patterns can be quite simple. Here we show
that when they are placed in fluid flow, kirigami cut sheets with various
patterns produce a verity of flow patterns in the wake. Through several sets of
experiments, we show that the kirigami sheets placed in flow can undergo static
or dynamic flow-induced instabilities as a result of which they can buckle or
undergo limit cycle oscillations, or they can remain stable while undergoing
very large elongations. These structural responses produce several different
types of fluid patterns in the wake. We show that vortices both at small scales
(scales comparable with the size of the individual kirigami cuts) and large
scale (scales comparable with the size of the sheet) are formed in the wake of
kirigami sheets. We also show that jets at different sizes can be formed and
directed passively using kirigami sheets. These results show the potentials of
kirigami sheets for passive flow control.

Fluid Dynamics