SCALABILITY OF THE FORCE OF A NORMALLY IMPACTING VORTEX RING ON A PLANAR SURFACE

Open Access
- Author:
- McErlean, Michael Raymond
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Michael H Krane, Thesis Advisor/Co-Advisor
Michael H Krane, Thesis Advisor/Co-Advisor
Arnold Anthony Fontaine, Thesis Advisor/Co-Advisor - Keywords:
- impact force
high-speed video
DPIV
vortex rings
surface pressure - Abstract:
- This thesis addresses one of the issues in developing a non-lethal vortex ring weapon. Such a weapon would take advantage of the transfer of momentum from a vortex ring to a target and the encapsulation of fluid within the vorticity core. By transfering its momentum, a vortex ring can knock over or capsize a target in air and water while carrying a chemical agent such as tear gas or marker dye to the target. Vortex rings of sufficient strength to accomplish these goals have been generated previously, but the relation between the initial strength of the vortex ring and the force that would be imparted to a target is unkown. This study hopes to provide the means for enabling a large scale, effective vortex ring weapon by derving a scaling relation for the vortex strength and measuring the impact in a smaller, laboratory setting. The analytical expression for the impact force of a vortex ring in a normal impact on a planar surface is derived using dimensional analyis of the ring properties. The relation is experimentally verified by measuring the impact force for vortex rings for a range of initial vortex ring strengths. The normal impact of a vortex ring with a planar wall has been examined for the motion of the vortex on the wall and the vorticity generated. However, the force generated by a vortex ring on a wall has never been measured experimentally. Experiments measuring the impact force, pressure on the surface, and motion of the vortex rings were conducted in a large glass tank full of quiescent water with the vortex rings generated by a piston-cylinder assembly. A planar wall was placed in the path of the vortex rings between 0.45 to 1 m from the nozzle. The planar surface was on a pivoting assembly with the force transducer anchoring the assembly above the water line. A pressure transducer was mounted flush with the wall. An extit{in situ} calibration was peformed on the measurement system using an impact hammer to ensure an accurate measure of the vortex ring impact force. The time evolution of the force and pressure on the wall was measured for four different ring strengths and at three distances from the nozzle. Concurrent to the force and pressure measurements, the motion of the vortex rings before and during impact was recorded with high-speed digital video camera (HSV). The high-speed images were analyzed to determine the speed and size of the rings and determine their changes during an impact. The flowfield of the vortex rings during an impact was measured with digital particle image velocimetry (DPIV) to determine the ring's size, speed, and strength. The measurements of the vortex rings obtained using HSV and DPIV combined with the force and pressure measurements were used to confirm the underlying assumptions made in deriving the analytical expression for force scaling before being applied to the relation itself.