Flows around rotating disks with and without rim-shroud gap

Experimental and numerical approaches have been used to study the effect of the radial rim-shroud gap on the flow structures found around a rotating disk in a finite cylindrical casing. When the radius of the disk and the inner radius of the casing are comparable and there is no radial gap, instabilities bring spiral rolls with a positive front angle in the Bodewadt layer on the end wall of the stationary casing. When the disk radius is smaller than the inner radius of the casing, vortex flows appear within the radial gap between the disk rim and the side wall of the casing. If the disk is thin, but not too thin, disturbances generated by these vortex flows proceed inward and the spiral rolls with a negative front angle appear in the Bodewadt layer. In the case of a thick disk, wavy Taylor vortex-like flow appears in the radial gap. The disturbances formed by the vortex flow do not well propagate into the inner region, and a flow pattern of bead-like vortices or a chain of vortices consisting of a series of small vortices are found around the disk in the visualized figure parallel to the disk.