SCALING PROPERTIES OF VORTEX RING FORMATION AT A CIRCULAR TUBE OPENING

A vortex sheet model is applied to study vortex ring formation at the edge of a circular tube, for accelerating piston velocities U-p simila r to t(m). We determine properties of the vortex ring as a function of the piston motion and investigate the extent to which similarity theo ry for planar vortex sheet separation applies. For piston strokes up t o half the tube diameter, we find that the ring diameter, core size an d circulation are well predicted by the planar similarity theory. The axial ring translation is a superposition of an upstream component pre dicted by the theory and a downstream component which is linear in the piston stroke. The front of the fluid volume exiting the tube is also linear in the piston stroke and travels with 75% of the piston veloci ty. The core size decreases and the distribution of fluid near the cor e becomes more asymmetric as the parameter m increases. (C) 1996 Ameri can Institute of Physics.