Characteristics of Transient Vortices in the Boundary Layer on a Rotating Disk under Orbital Motion

The objective of this study is to experimentally examine the characteristics of transient vortices in the boundary layer on a disk undergoing both rotation and orbital motion. The velocity fluctuations on a rotating, orbiting disk (disk radius equal to orbital radius) are measured by the hot-wire method, and the effects of orbital motion on the transient vortices in the boundary layer are examined. When the ratio of the orbital speed to the speed of rotation is ±0.025, the interval of transient vortices depends on only the orbital radius, regardless of the directions of rotation and orbital motion. The rate of low-frequency disturbances increases as the orbital speed increases, and the vortices induced by these low-frequency disturbances travel over the disk and then develop in the region of increased velocity. Consequently, no vortices generated on a rotating disk under orbital motion are stationary relative to the disk.