Drag reduction of an enclosed rotating disk with fine spiral grooves

Abstract

The purpose of this study is to obtain the new type of the drag reduction for the frictional moment of an enclosed rotating disk by using the fine spiral grooves on the disk surface. The experiments were carried out the measurement for the frictional moment of an enclosed rotating disk with fine spiral grooves, of which there were 120-160 in the number and 0.1-0.2 mm in depth, respectively. The Reynolds number range is 4 × 104 Re ≤ 6 × 105. Test fluids are tap water and aqueous solutions of glycerin. It was seen that the drag reduction occurs in the turbulent flow range at the non-dimensional axial clearance (s/a)=0.011, 0.22 and 0.33, the maximum drag reduction ratio is approximately 15%. The drag reduction depends on the number, the angle and the depth of the grooves. The fine spiral groove has the effect which suppresses the development of the fluctuation of transition region, and which delays the generation of the local turbulence in the transition range.