Effectiveness of Slippery Liquid Infused Porous Surface in Viscous Drag Reduction in Boundary Layers at Varying Reynolds Numbers
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Drag in marine vehicles is unavoidable but a decrease of the drag is always a perused aim. With modern technologies, it is critical to investigate the new opportunities for achieving reduced drag on the marine vessels and using less fuel to propel them. This work investigates the effect of Slippery Liquid Infused Porous Surface (SLIPS) on surface-water interaction at varying regimes of flow. This work is focused on understanding the potential effects of SLIPS on drag reduction of water flow over solid surfaces and ships. The SLIPS used in the process was created on the surface of aluminium 5083 due to the fact that, this material is commonly used in marine industry. The method was based on an existing one but with significant modifications. The microstructure is finer but nano-structure is the same. This is achieved by anodising, boehmiting and infusing with silicon oil. In order to conduct this investigation a number of experiments were done using well-known methods. These involve measuring and comparing the torque required to rotate a disk with and without treatment as an initial set of tests. Since the flow regime may vary along the radius of the disk, additional experiments were conducted with rotating coaxial cylinders. In the final stage of the study, a model of a boat was towed in the Australian Maritime College basin in Launceston, Tasmania. Comparison of the required force or torque to move treated and non-treated objects at a specified speed show that drag reduction occurs in laminar or dominantly laminar flow but significantly decreases with increase of the turbulences in the flow. A typical drop in resistance is about 3% to 4.5% for the mean values for rotating disk. Rotating coaxial cylinders tests show bigger drag reduction for a laminar regime: up to 40%. With the development of the turbulence, it falls to 3% and even lower. An interesting phenomenon was found during the tests associated with the observed vibrations. The reduction in resistance is up to 40% in these conditions but this requires a study that is more detailed and focused on that phenomenon. The model boat was tested without SLIPS and with SLIPS. Assuming that the residuary resistance is the same in both cases, it was derived from the non-treated boat test and used for calculating the friction resistance of the treated boat. Using the derived frictional resistance and frictional coefficient from the towing test of the model, a rough estimation was made of the total resistance of the full-size vessel. For the estimated mean frictional resistance drop of 3%, the total resistance of the ship is expected to decrease between 0 to 1.5%.