Three-dimensional flow separations on a rolling sphere

Experiments are conducted to study the flow separations on a sphere rolling on an inclined plane submerged in water. These experiments are performed at Reynolds numbers Re between 1350 and 1550. The experiments show that the flow separations on the surface of a rolling sphere can be organized into four distinct regions: (i) region of primary separation-I on the front upper sphere and extending below the poles, (ii) region of viscous blockage at the crevice surrounding the point of contact and shear layer separation ahead and at the sides of the viscous blockage, (iii) region of primary separation-II on the rear lower sphere and (iv) secondary separations on the rear upper sphere surface. The ratio of the width of the viscous blockage to the diameter of the sphere is found to be 0.4. Primary separation-I surface is symmetrical about the equatorial plane of the rolling sphere. Primary separation-II from the rear lower sphere surface is asymmetrical about the equator and eddies are shed alternately on either side of the equator from this separation surface. These lower eddies are energetic and dominate the dynamics of the wake. The upper eddy shedding from the primary separation-I surface and the lower eddy shedding from the primary separation-II surface are synchronized.