Drag on a partially immersed sphere at the capillary scale
Robert Hunt, Ze Zhao, Eli A. Silver, Jinhui Yan, Yuri Bazilevs, Daniel M. Harris
Abstract
Drag on a sphere in a steady flow is an important and thoroughly studied problem in fluid dynamics, yet relatively little work includes the effects of a free surface. Through experiments and simulations, we characterize the drag on a sphere partially immersed at an air-water interface as a function of submergence depth. The presence of the free surface can induce drag forces several times greater than the equivalent fully submerged case, with pronounced hysteretic effects strongly influenced by the sphere's wettability. We ascribe the drag increase to an asymmetric pressure loading on the sphere that persists for flows both above and below the minimum capillary-gravity wave speed.