Skin Friction Developments Associated With Vortex Ring-Sphere Interactions

Abstract Skin friction developments resulting from coaxial and non-coaxial collisions between a ReG0 = 3000 vortex ring and stationary spheres have been explored using Large-Eddy Simulations. The diameter ratio (D/d), which is the ratio between sphere diameter (D) and initial vortex ring diameter (d), ranges from 1 to 4. Axis of the initial vortex ring is offset by δ/D = 1/8 to 1/2 to explore the effects of offset distance on skin friction evolution. For coaxial collisions, collision of primary vortex ring with the sphere usually produces the largest skin friction magnitude, which also increases with the diameter ratio. However, high-magnitude skin friction levels cover increasingly smaller regions as the diameter ratio increases. For non-coaxial collisions, skin friction evolutions differ significantly between the end closer to the sphere axis and the end further from it. Skin friction magnitude resulting from the collisions of primary vortex ring at the end closer to the sphere axis is considerably higher than that at the end further from the sphere axis, despite being more confined by the blockage imposed by the sphere top. Nevertheless, the skin friction induced by the primary vortex core at the end further from the sphere axis is often relatively lower but extends further downstream.