Superhydrophobic coatings for drag reduction and noise control of circular cylinders in air flow

A superhydrophobic coating has been assessed for its ability to reduce both aerodynamic drag and aeroacoustic noise for a cylinder in a cross-flow of air. Drag contributes significantly to the operation costs of transportation vehicles as well as to greenhouse gas and dangerous NO_x emissions. In addition, pervasive noise pollution threatens public health, socio-economic development, and ecological systems. Many technological solutions to reduce both drag and noise from bodies moving through either air or water have been researched and developed to date. In the current work, a superhydrophobic coating, which is typically used for the reduction of hydrodynamic drag in water was assessed in air in an attempt to identify a cross-disciplinary opportunity. A polymer coating containing S iO2@TiO2 coreshell nanoparticles in a solvent-based polyurethane binder was applied to a 22 mm diameter aluminium cylinder and tested in aerodynamic and aeroacoustic wind tunnels. Free-stream velocities were varied from 10 m/s to 60 m/s, corresponding to a Reynolds number range of 1.4×10⁴ to 8.4×10⁴ based on the cylinder diameter. Drag reductions of up to 11% and noise reductions of 3-4 dB were measured compared to reference uncoated and smooth cylinders.