Drag Reduction for a Rotating Disk with Highly Water-Repellent Wall

Abstract

Using a highly water-repellent coating wall, new type of drag reduction for a rotating disk in Newtonian fluid have been clarified experimentally. Measurements were carried out to measure the moment of rotating disks with highly water-repellent-wall and with smooth aluminum wall. The clearance between the disk and the housing wall was varied at 5, 10, and 20 mm thick. Tested fluids were tap water and aqueous solution of glycerin at concentration of 30 wt% ahd 40 wt%. The experimental data of the moment of the rotating disk with highly water-repellent wall in housing decreased comparing with the data of smooth plane disk. It was shown that the maximum drag reduction ratio was about 45% in aqueous solution of glycerin at concentration of 40 wt%, and that the viscous properties had a slight effect upon the drag reduction.