Viscous drag reduction by micron sized surface roughness

为了实现HSCT和超级巨型飞机的概念，需要发展层流控制和湍流管理技术。同时，这些技术将被有效地应用于常规流体机械和能量交换设备的精炼，以降低污染因子。也就是说，三维边界层转变及其控制的研究是流体科学领域中的重要技术问题之一。本课题是与这一重要应用研究领域相关的两年基础性研究。第一年，对平板表面采用微米级均匀粗糙度的湍流管理进行了实验研究。为此，研制了高精度的阻力测量系统，并进行了系统的测量。通过研究，在表面厚度为9微米的情况下，减阻效果约为1%。脊形表面的减阻机理通常用表面几何结构中的流向微米级沟槽结构来解释。既然均匀分布的粗糙表面几何形状也表现出减阻效果，我们需要考虑另一层，因为减阻率与表面粗糙度之间存在的体积成正比，在那里低动量边界层流动可以停留，我们得出结论，表面几何形状中的体积对减阻非常重要。第二年，研究了特殊扰动的粗糙表面和纺织品表面过渡边界层中的过渡延迟机理。也就是说，在特殊过渡边界层被钢丝绊倒的情况下，在某些织物表面观察到有效的过渡延迟或显著的减阻。

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.