Ring Vortices - . In recent conflicts our military interact with civilians either in battles or violent demonstrations so non-lethal weapons must be reconsidered, after earlier programs were terminated. Analytical and experimental efforts regarding the ring vortex generators started 50 years ago when I operated my open channel shock tube in the engine laboratory of U.C. Berkeley. The initial shock wave created by the outflow from the tube startled people who, if they were in the line of fire, reacted violently to the ring vortex that followed. No harm was done, but all avoided the expected trajectory of the vortices. Sudden efflux from a tube produces a ring vortex entraining ambient fluid and traveling distances thousands times their diameters with little dissipation, (Fig. 1). Operators of aircraft know this and avoid closely following aircraft ahead of them because wing tip vortices can roll aircraft miles away. There is some evidence of U.S. Navy tests of detonations of propane-oxygen mixtures in 3" diameter pipes. These produced 2 foot diameter ring vortices that traveled at 750 ft/s and shredded trees 1/4 mile away. The base for these tests has been closed for decades and the guards at the gate, no uniforms, knew nothing; not even who was paying them. Germans invading the Soviet Union in 1941 captured a test range where 6 grams of explosive generated ring vortices that impacted targets with a force of 250 kilograms. Ring vortices from rifle fire traveled at 70 m/s and broke car windows at 300 meters. Germans were so impressed that they started research to use ring vortices against allied bombers. My interest in this field was revived by the U.S. Army research program in non-lethal weapons responding to worldwide accusations of massacring civilians in revenge for the Black Hawk disaster. My expressions of interest in Army's inquiry yielded several contracts to demonstrate working equipment. I developed a cyclic ring vortex generator in which propane and compressed air were injected into a chamber where they mixed, were ignited and exhausted through a tube, (Fig. 2 & 3). The ultimate goal was to cycle at 12-15 Hz because it was known that humans shaken briefly at such frequencies become disoriented and incontinent.
Experimental Data - Experiments yielded fundamental data on mixing and development of Mach 6 detonation waves that produced 3000 ft/s outflow from tubes and created ring vortices traveling at Mach 3.
Utilization of Ring Vortex Generators - Smallest man- portable generators could fire 1000 times using about 62 pounds of oxygen at 2000 psi and liquid propane. Larger units on light vehicles could keep crowds at distances of 200-300 yards. At shorter ranges firing of the weapon would produce flaming exhaust, crack of a Mach 6 shock wave and a ring translating at 750 ft./s, with equal swirl speed at its circumference. Such spectacle should persuade most rioters to retreat..