Dynamic kirigami structures for wake flow control behind a circular cylinder.

A flow passing through a bluff body can produce Karman shedding vortex streets in its wake flow, resulting in strong unsteady loading and vibration. Existing passive control methods can disturb the wake flow, but are usually effective only under certain conditions and cannot adapt to changing environments due to their fixed topographies. Kirigami structures (the art of paper cutting) demonstrate programable out-of-plane buckling deformation under simple force actuations. By stretching and relaxing these kirigami sheets, an array of tilted surface elements can be easily activated and deactivated on the surface of a bluff body. For the first time, kirigami structures are used to achieve dynamic passive flow control. The control performance on the wake flow of a cylinder is validated in a wind tunnel using particle image velocimetry. Activated kirigami structures can push the shedding vortices further downstream from the cylinder by about four times of the uncontrolled one and reduce peak values of the turbulent intensity and Reynolds shear stress by 70% and 50%, respectively. The control performance is largely dependent on the height and shape of the kirigami structures. [ABSTRACT FROM AUTHOR]