Experimental Study of Air Layer Sustainability for Frictional Drag Reduction

Abstract

Frictional drag reduction by microbubbles is a promising engineering method for reducing ship fuel consumption, especially for large, slow steaming vessels. Total resistance can be broken down into frictional drag and form drag (also known as pressure drag or profile drag). Ship's hull form optimization is commonly to reduce the form drag of a ship. Another technique would be required to deal with the frictional (viscous) portion of the total resistance. One such technique that reduces the friction resistance is the air lubrication technique. This research looks at possible enhancement for the microbubbles drag reduction technique with the use of hydrophobic plates to trap and retain an air layer. The hydrophobic surface cannot sustain bubbles by itself. Laser-machined microstructure coupled with hydrophobic coatings allows the rapid formation of air layer rapidly and sustainability of the air layer is recorded. With extensive experimental studies, we have shown that an air layer can be entrained around a moving flat plate thereby reducing friction. This could pave the way for applying this technique around the wall of moving ship hulls thereby minimizing the viscous drag and reducing the shipping costs.