Demonstration of Drag Reduction Using Nanotube Coated Hydrophobic Surfaces

With higher fuel costs and desire for ehanced performance, new techniques for improving efficiencies in marine propulsion are required. The reduction of the viscous drag is one such technique. Various active and passive measures have been extensively researched with mixed results for total energy savings. However, recent research in microfluidics has indicated significant drag reduction using super-hydrophobic surfaces. To achieve this, a low free energy surface with micro-scale roughness is required. One promising technique uses chemically treated nanotubes as the super-hydrophobic surface which results in high contact angles with low hysteresis. However, previous methods for creating these nanotube coated surfaces are not feasible for manufacturing large-scale structures due to cost and complexity. Mainstream will rely on its expertise in innovative fabrication processes for nanotubes to demonstrate super-hydrophobic surfaces using chemically treated nanotubes that are feasible for large-scale surfaces. The Phase I effort will characterize the optimum properties of the nanotube coated hydrophobic surface and demonstrate the feasibility of this surface for macro-scale drag reduction using small-scale test surfaces in a fully turbulent flow through computational and experimental methods. Phase II will fabricate and test nanotube coated hydrophobic surfaces of model size with Reynolds numbers typical of marine vessels. BENEFITS: The drag reduction capability using nanotube coatings will have application for a variety of commercial marine vessels used within the private and military sectors to improve fuel efficiency and/or allowing for increased maximum velocity. This technology has a potential to be used with an anticorrosive or anti-fouling coating for long life within wetted conditions thereby reducing maintenance costs.