柔軟リブレット面の乱流遷移に及ぼす影響

抄録

We investigated the influence of the wall surface properties on the drag reduction and turbulent transition from the viewpoint of the surface flexibility. The flow rate and pressure loss were measured for the water flows in a rectangular channel with an aspect ratio of ten. The test surfaces were the smooth surface, home-made fiber-flocking (flexible riblet) surface, and the 3D-printed rigid riblet surface. The flexible and rigid riblet surfaces have the same shape. A confocal laser microscope confirmed that the flexible and rigid riblet surfaces have almost an identical dimension. As a result of the present experiment, we mainly obtained following findings. First, the flexible riblet surface caused the delay of turbulent transition, while the rigid one didn’t. Second, it was found that both surfaces showed almost the same maximum drag reduction ratio, but the flexible riblet surface had the smaller drag reduction region of the Reynolds number than that of the rigid one. Third, the roughness effect of the rigid riblet surface was larger than that of the flexible one at the higher Reynolds number.