50% of the total drag of many ships and submarines [1]. Thus, researchers have devoted their efforts to the quest for surfaces with reduced drag to be applied on marine vessels. Bioinspired, liquid-repellent surfaces have been intensively investigated for this application. However, the well-known superhydrophobic surfaces have proven unsuitable for underwater conditions, due to the loss of trapped air pockets. On the other hand, Slippery Liquid-Infused Porous Surfaces (SLIPSs) have provided encouraging results in terms of drag resistance reduction and long-term stability [2]. However, further studies are needed to establish more solid relationships between SLIPS engineering and their drag resistance properties. In this work, we have fabricated and tested SLIPSs with different infused oils. All these SLIPSs were based on a randomly oriented, nanostructured boehmite coating combined with an organic layer to promote retention of the infused liquid. Perfluoropolyethers, silicone oils and n-hexadecane were used as infused liquids. The drag resistance behavior of SLIPSs has been tested in three experiments involving different scales and flow régimes: ? Visualization of the rolling/sliding motion of a single drop on a tilted surface ? Measurement of the torque in a Couette-like flow apparatus (laminar conditions) ? Measurement of the wall shear force in a high-speed boundary layer over a large flat plate (turbulent conditions). Preliminary results indicate that a careful design of SLIPSs is necessary to achieve the best compromise between drag reduction and long-term stability, particularly when the more challenging requirements typical of real, high-Reynolds number flows must be considered. [1] Perlin, M.; Dowling, D. R.; Ceccio, S. L. Freeman Scholar Review: Passive and Active Skin-Friction Drag Reduction in Turbulent Boundary Layers. J. Fluids Eng . 2016 , 138 (9) , 091104. [2] Rosenberg, B. J.; Van Buren, T.; Fu, M. K.; Smits, A. J. Turbulent Drag Reduction Over Air- and Liquid-Impregnated Surfaces. Physics of Fluids 2016 , 28 , 015103.
SLIPSs with Reduced Skin-Friction Resistance
Federico VERONESI;Mariarosa RAIMONDO;Elena CIAPPI;
2019
Abstract
50% of the total drag of many ships and submarines [1]. Thus, researchers have devoted their efforts to the quest for surfaces with reduced drag to be applied on marine vessels. Bioinspired, liquid-repellent surfaces have been intensively investigated for this application. However, the well-known superhydrophobic surfaces have proven unsuitable for underwater conditions, due to the loss of trapped air pockets. On the other hand, Slippery Liquid-Infused Porous Surfaces (SLIPSs) have provided encouraging results in terms of drag resistance reduction and long-term stability [2]. However, further studies are needed to establish more solid relationships between SLIPS engineering and their drag resistance properties. In this work, we have fabricated and tested SLIPSs with different infused oils. All these SLIPSs were based on a randomly oriented, nanostructured boehmite coating combined with an organic layer to promote retention of the infused liquid. Perfluoropolyethers, silicone oils and n-hexadecane were used as infused liquids. The drag resistance behavior of SLIPSs has been tested in three experiments involving different scales and flow régimes: ? Visualization of the rolling/sliding motion of a single drop on a tilted surface ? Measurement of the torque in a Couette-like flow apparatus (laminar conditions) ? Measurement of the wall shear force in a high-speed boundary layer over a large flat plate (turbulent conditions). Preliminary results indicate that a careful design of SLIPSs is necessary to achieve the best compromise between drag reduction and long-term stability, particularly when the more challenging requirements typical of real, high-Reynolds number flows must be considered. [1] Perlin, M.; Dowling, D. R.; Ceccio, S. L. Freeman Scholar Review: Passive and Active Skin-Friction Drag Reduction in Turbulent Boundary Layers. J. Fluids Eng . 2016 , 138 (9) , 091104. [2] Rosenberg, B. J.; Van Buren, T.; Fu, M. K.; Smits, A. J. Turbulent Drag Reduction Over Air- and Liquid-Impregnated Surfaces. Physics of Fluids 2016 , 28 , 015103.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
