Viscous drag reduction by micron sized surface roughness

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Development of Laminar Flow Control and turbulence management technique are needed in order to bring the concept of HSCT and Super Jumbo aircraft into reality. At the same time, these technique will be effectively applied to refine conventional fluid machineries and energy exchanging machines for the purpose of lowering the pollution factors. Namely, investigation of the three dimensional boundary layr transition and its control is one of the important technological issue remained in the field of fluid science. Present research project is the fundamental two year research related to such important applicative research firld. In the first year, turbulence management using micron-sized uniform roughness on a flat plate surface is investigated experimentally. For such purpose, high accuracy drag force measuring system is developed and systematic measurement is performed. Through such investigation, about 1% drag reduction is obtained in the case of 9 mum surface. Drag reduction mechanism in the case of Riblet surface is always explained with streamwise micron-sized grove structure in the surface geometry. Now that uniformly distributed roughness surface geometry showed also drag reduction, we need to consider another story for the drag reduction rate is proportional to the volume existing between the roughness in the surface there the low momentum boundary layr flow can stay, we came to the concluasion that such volume in the surface geometry is very important for the drag reduction.In the second year, transition delay mechanism in the specially disturbed transitional boundary layr on rough and textile surfaces is investigated. Namely, effective transition delay, or prominent drag reduction is observed in the case of some textile surfaces in the case of special transitional boundary layr tripped by a wire.