"Turbulent flow control through super-hydrophobic surfaces"

Shear flows, abundant in nature, can take the form of ocean, mantle, atmospheric convection, or other geophysical flows. Large-scale fluid structures, or secondary flows, can dominate the flows within these shear flows and cause changes to their surroundings; such a change can be found, for example, in atmospheric convections that bring rain, whereby secondary flows can facilitate pollutant transport which accelerates climactic events such as ozone depletion or global warming. The Taylor-Couette (TC) flow is a canonical model that scientists can use to study such secondary structures. The TC flow is described as a shear flow between two independently rotating co-axial cylinders. When secondary flows in the TC flow are pinned, they are called Taylor rolls; Taylor rolls can drastically affect flow behavior such as, for example, by hindering homogenous mixing even at high Reynolds numbers. We study the possibility of influencing these secondary structures, by interfering with the Reynolds stress that generates these Taylor rolls, in order to enhance mixing homogeneity. We achieve this by modifying the surface of the inner cylinder, using alternating super-hydrophobic (SHP) and no-slip surfaces in spanwise patterns on its surface at Rei = 104 to 2 × 104. We compare experiments of these inner cylinder surface modifications that affect the Taylor rolls and cause drag reduction.