1 p.m. - 2 p.m. Location: SLC 2.302
Turbulent drag reduction over Liquid Infused Surfaces
Turbulent drag reduction has been the objective of research studies for several decades, but with the possible exceptions of non-Newtonian additives and riblets, all attempts so far have failed to deliver any noticeable effect under realistic flow conditions. Such conditions are highly turbulent, with Reynolds numbers several orders of magnitude higher than those experienced in laboratory studies of drag reduction.
One of the most promising methods for drag reduction is that of Super-Hydrophobic Surfaces (SHS), allowing for entrapment of air, which reduces the effective shear of the surface. Unfortunately, these surfaces are typically plagued with problems, such as limited oleophobicity with high-contact-angle hysteresis, failure under pressure and upon physical damage, inability to self-heal and high production costs. Liquid Infused Surfaces (LIS) present a novel method for passive, turbulent drag reduction. They consist of a film of lubricating oil locked in place by a micro/nanoporous substrate. LIS have negligible contact angle hysteresis, low sliding angles for drops on the surface, extreme pressure stability. Direct Numerical Simulations of the turbulent channel flow over Liquid Infused Surfaces have been performed. Numerical results reveal that drag reduction is obtained only when the interface between the two fluids is stable and pinned to the ridges. A parametric study varying the viscosity of the two fluids, the shape of the textured surface and the interfacial tension has been carried out to develop design criteria for practical applications. Numerical results and experiment show that the turbulent drag is reduced by up to 25%. An attempt to reconcile, drag reduction and rough wall under the same framework will be discussed at the seminar.