各種粘弾性流体中を落下する球の抗力に及ぼす粘弾性マッハ数の影響

抄録

Drag forces of a falling sphere are experimentally studied in viscoelastic fluids such as wormlike micellar fluids and polymer solutions. Experiments are performed for spheres with the same size and different densities, and the drag force acting on the sphere is evaluated at its terminal velocity. In viscoelastic fluids, shear waves can be propagated, and the viscoelastic Mach number is defined as the ratio of the speed of an object in a fluid to the speed of shear waves in the fluid. The drag force measurements show that the damping characteristics of shear waves play an important role in the drag dependence on the falling speed. In the fluid with lower damping characteristics, the drag dependence on the falling speed changes significantly at a Mach number of unity, which is attributed to the formation of a Mach cone around a sphere accompanied by a jump in the vertical velocity across the Mach cone.