PROJECTS: VORTEX CANNONS
TUB THUMPING CANNON
BARKING TUBE CANNON
HOW IT WORKS
Just as a sphere (ball) is the natural shape for solids
to roll on a surface, the toroid (donut) is the natural
shape for a gas to “roll” axially through space.
As air moves forward through the toroid’s inside
edge, it draws air back around from the outside edge
to replace it. The moving air exerts less pressure than
the still air around it, so it stays in the donut shape.
Making a traveling vortex is easy: just push a puff
of air evenly through a wide circular aperture. As the
puff emerges, surrounding air travels in to fill the low-pressure zone behind it. This pinches it off and curls it
back on itself to form the ring. You can make the ring
visible by using smoke or fog from a fog machine.
An empty, topless gallon milk jug will make a vortex if
you thump its bottom. The “Tub Thumping” cannon here
is a larger version based on a garbage can.
The “Barking Tube” cannon uses a subwoofer to
push out a series of vortices. The velocity curve of the
impulse affects the vortex ring: an accelerating push
makes it fly faster, while a decelerating push adds spin,
making it fly slower and disintegrate dramatically.
The “Big Bad Boom” cannon (instructions online at
makezine.com/15/vortex) launches a vortex strong
enough to travel outdoors (if it isn’t windy).
1 Puff of air travels forward
2 Low pressure aft forms toroid vortex
3 Trash-bag diaphragm makes puffs
4 Subwoofer pumps series of vortices
5 Audio gear controls vortex frequency
6 Fog machine makes vortex visible
7 PVC air cannon makes strong vortex
BIG BAD BOOM CANNON
Illustation by Damien Scogin
116 Make: Volume 15