Viscous Drag Reduction Using Hydrophobic Surface

It has been shown that hydrophobic surfaces can reduce skin-friction drag in micro-fluidic devices. During Phase I research, we will fabricate and test a high performance durable hydrophobic surface coating created by a simple, cost-effective, and environmentally friendly method. This coating could have significant effects on skin-friction drag reduction and/or transition delay in boundary layers. This surface modification on Navy vessels and underwater munitions would enable significantly reduced cost of operation and increased performance. We will estimate and characterize the required properties, such as the slip length, of the hydrophobic surfaces in these preliminary analyses and demonstrate the desired effect using numerical simulations and small-scale laboratory experiments. Based on the coatings fabrication design developed in Phase I, during Phase II we will fabricate a hydrophobic surface large enough to cover a substantial part of the model vessel (surface ships or submersibles) and directly test drag reduction in tow tank and/or water-tunnel experiments.BENEFITS: The major goal of this research plan is to develop hydrophobic surface coatings that reduce the transition to turbulence, turbulent skin friction and turbulent pressure fluctuations that occur at the ship-water interface during motion. These coatings would be widely applicable for use on surface ships, underwater transport vehicles and munitions and have considerable benefit by increasing vehicular performance. Reduction of the turbulent skin friction would enable increases in overall top speeds as well as enhancing effective range. The ability to delay the onset of transition to turbulence would also have similar effects by reducing the total vehicle drag. Reduction of turbulent skin friction would have major economic implications, particularly for cargo transport. Drag reduction would result in significantly reduced fuel consumption, thus leading to lower shipping costs, and providing tremendous benefit both to military and commercial water transport systems.