Flow measurement around the edges and curved outer surface of a rotating disk

An experimental study is performed to investigate the flow structures near the edges of rotating disks with di ff erent edge shapes. By changing the rotational speed, the Reynolds number is changed from 277 to 356. It is found that the fluid motion near the sharp edge di ff ers depending on whether a rotating shaft is at the disk surface. A flow developing on the flat side of the disk surface changes its direction toward the curved outer surface on the shaft side, and the flow goes straight outward, leaving the disk on the flat side. The existence of the supporting shaft increases the radial velocity of the flow while decreasing the azimuthal velocity. The e ff ects of the edge shape of the disk on the flow fields are also investigated by changing the shape of the disk edges. Rounded and chamfered edges have no noticeable e ff ect on the azimuthal velocity on the curved outer surface, whereas changing the edge shape enhanced the velocity in the disk-thickness direction. In the FFT analyses of the azimuthal velocity measured at the edge of the curved outer surface when the disk edge is rounded, an increase in power across a range of frequencies is observed. Only in the chamfered edge disk case, a peak in the spectrum of the velocity that corresponds to a wavenumber which appears in the transitional boundary layers is observed.