Drag Reduction In Turbulent Flows Over Micropatterned Superhydrophobic Surfaces

• Main Author: Daniello, Robert J.
• Format: Others
• Published: ScholarWorks@UMass Amherst 2009
• Subjects: superhydrophobic; drag reduction; turbulence; micropatterned; ultrahydrophobic; Fluid dynamics; Fluid Dynamics; Ocean Engineering; Other Chemical Engineering; Other Mechanical Engineering; Transport Phenomena
• Online Access: https://scholarworks.umass.edu/theses/316; https://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1397&context=theses

Periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide drag reduction in the laminar flow regime, have been demonstrated capable of reducing drag in the turbulent flow regime as well. Superhydrophobic surfaces contain micro or nanoscale hydrophobic features which can support a shear-free air-water interface between peaks in the surface topology. Particle image velocimetry and pressure drop measurements were used to observe significant slip velocities, shear stress, and pressure drop reductions corresponding to skin friction drag reductions approaching 50%. At a given Reynolds number, drag reduction was found to increase with increasing feature size and spacing, as in laminar flows. No observable drag reduction was noted in the laminar regime, consistent with previous experimental results and theoretical predictions for the channel geometry considered. In turbulent flow, viscous sublayer thickness appears to be the relevant length scale as it approaches the scale of the superhydrophobic microfeatures; performance was seen to increase with further reduction of the viscous sublayer. These results indicate superhydrophobic surfaces may provide a significant drag reducing mechanism for marine vessels.