Investigation of the supression of turbulent vortex formation and the frictional drag reduction effect on ship hull due to hydrogel painting

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Hydrogel painting for ship hull makes hydration layer in sea water and has various functionalities. In this study, we revealed the effect of frictional drag reduction with hydrogel painting surface based on the relation with turbulent vortical structure formation. In experiment, we made a rotating annular cylinders apparatus with painted surface on the inner cylinder, and measured the torque acted on the inner cylinder. From experimental data, it was shown that the drag reduction effect of hydrogel painting became strong when the thickness of painting layer became small. In addition, we carried out the numerical simulations of channel flow with local slip velocity and penetration of fluid into wall, and found that the drag reduction effect depended on the scale of turbulent vortex structure and the thickness of boundary layer.