Effects of a radial gap on vortical flow structures around a rotating disk in a cylindrical casing

The flow generated by the rotation of the disk in a stationary cylindrical casing is investigated by the numerical and experimental approaches. When the rotating disk has finite radius and thickness, there exists the axial gap between the disk surface and the end wall of the casing and the radial gap between the disk tip and the side wall of the casing. The flows in these gaps show complex flow structures depending on the geometric and kinetic parameters. In this study, five disks with different radii are introduced and the effects of the radial gap width and the Reynolds number on the flow structures are investigated. The flow with steady Taylor vortices emerges in the radial gap at relatively low Reynolds numbers. When the Reynolds number is moderate, Taylor vortices in the radial gap have the wavy structures in the azimuthal direction. The flow with the wavy structure is classified into two types: one is the normal mode and the other is the anomalous mode. The latter type has the extra vortices at the corner of the casing. At the higher Reynolds numbers, the turbulent Taylor vortices appear in the radial gap. In this case, the disturbances in the radial gap propagate inward along the end walls of the casing and the spiral vortices occur near the disk tip in the upper and lower axial gaps. The dependency of the flow structure on the radial gap width is clarified.