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DRAG REDUCTION PERFORMANCE OF FDR-SPC (FRICTIONAL DRAG REDUCTION SELF-POLISHING COPOLYMER)

In this study, a novel skin-friction reducing polymer named FDR-SPC (Frictional Drag Reduction SelfPolishing Copolymer) has been synthesized. The drag reducing functional radical such as PEGMA (Poly(ethylene) glycol methacrylate) has been utilized to participate in the synthesis process of the SPC. The types of the baseline SPC monomers, the molecular weight and the mole fraction of PEGMA were varied in the synthesis process. In the high-Reynolds number flow measurement with a flush-mounted balance and a LDV (Laser Doppler Velocimeter), the skin friction of the present FDR-SPC is found to be smaller than that of smooth plate in the entire Reynolds number range, with the average drag reduction efficiency being 13.5% over the smooth plate. INTRODUCTION The reduction of frictional drag of turbulent boundary layer is of great importance for the fuel economy of ship. Along with the development of hull form optimization technique, the wavemaking resistance has become less than 20% of the total drag of most modern ships. Therefore, the advantage from the reduction of the remaining frictional drag would be enormous. The fuel consumption of global ocean shipping in 2003 was estimated 2.1 billion barrel/year (Corbett and Koehler, 2003), which corresponds to approximately 200 billion US$/year. Thus, 10% reduction of frictional drag would lead to saving of 16 billion US$/year. The skin frictional drag is closely associated with the coherent structures, e.g. hairpin vortices in the turbulent boundary layer flow. Various control strategies toward the attenuation of the drag-inducing flow structure have been proposed during several decades. One of the most effective drag reduction strategies is the polymer injection, which was first introduced by Toms (1949). Toms (1949) found that addition of few ppm of a high molecular weight polymer to a turbulent water flow can result in large (up to 80%) reduction of skin friction drag. Added long chain polymer molecule extracts the turbulent energy out of the adjacent flow by coiling its chain structures and then releases the energy by becoming stretched back in the shear flow. The turbulent energy transfer between the freestream and the near-wall flow is thus interfered, leading to a significant skin friction reduction. This is named Toms effect after who discovered it. The polymer injection has been put into practice for the pipeline transportation of petroleum, demonstrating one of the most effective examples of drag reduction. It has been suggested that the polymer injection be applied to the frictional drag reduction for ships. There have been various researches to exemplifying the drag reduction efficiency of polymer injection in turbulent boundary layer (Brasseur et al. 2005, Li et al. 2008, Somandepalli et al. 2010). From the aspect of implementation, however, the polymer injection is impractical for ship application. This is because it necessarily requires the injection holes to be installed onto the hull surface, which would cause significant structural strength issues. As a feasible alternative to the polymer injection method, Yang et al. (2014) proposed a PEOcontaining AF paint. They reported the release of PEO, the well-documented drag reducing agent leading to Toms effect, from the surface of coating. It was found that the 1 June 30 July 3, 2015 Melbourne, Australia 9 5A-1