Not Just Another Old Flame
NASA scientists have discovered unexpected spiral-shaped
flames on Earth. By studying these peculiar flames, researchers
hope to mitigate fire hazards on spacecraft and gain new insights
about complex systems in nature.
May 12, 2000 -- The forms
of flames on Earth are familiar to everyone. We all know what
a burning match, candle, fireplace or blowtorch look like --
or a burning building, or rocket ignition blast. The presence
of gravity and the effects of air or gas movement, plus the type
of fuel and oxidant, determine everything from a flame's shape
and temperature to burn rate, burn pattern, soot production and
deposition and how fast it will or won't be extinguished.
"But in the microgravity of space, we are not dealing with just another old familiar flame," says Dr. Vedha Nayagam of NASA's National Center for Microgravity Research on Fluids and Combustion at the Glenn Research Center (GRC) in Cleveland, OH, where the nature of combustion in space is being studied intently by teams of scientists.
Above: On Earth, gravity-driven buoyant convection causes a candle flame to be teardrop-shaped (A) and carries soot to the flame's tip, making it yellow. In microgravity, where convective flows are absent, the flame is spherical, soot-free, and blue (B). [more information]
"The absence of gravity's effects on convection aboard the Space Shuttle, a space station or other space vehicle makes flames behave in ways that can be either beneficial -- as a test bed for research -- or very dangerous in the case of a fire in materials, chemicals or electrical devices. It is vital to know what makes flames start and stop in low gravity, and how flames behave while burning. The safety of NASA's space crews and vehicles can depend on our knowledge of combustion in space."
Watching the Flame Go 'Round
Recently, Dr. Nayagam and Dr. Forman Williams of the University
of California at San Diego, a co-investigator in NASA/GRC's microgravity
combustion science program, came upon some startling discoveries
about flames on Earth that could help scientists understand how
flames behave in microgravity.
Right: Flames on top of a disk slowly spinning in a clockwise
direction burn in a spiral headed counterclockwise. Vedha Nayagam
and Forman Williams are studying this phenomenon, which occurs
both on Earth and in microgravity, in the hopes of fully explaining
the pattern with basic physics principles.
Starting a fire at the center of a still disk is like dropping a stone in a quiet pond, says Nayagam. It produces a flame front that moves outward in a circle, fading as the fuel (the disk) is consumed. If you spin the disk, then the circular disk flames become spiral flames under some conditions.
"Under slow spin conditions ... just before circular
flames extinguish, [the flames] break symmetry -- and spirals
appear in the center hole of the flames and propagate outwards
in a spiral instead of in a circular wave front," he explained.
"Spiral burning could be common in the slow, swirling flows that we can establish in a microgravity environment -- but these results were very unexpected in normal Earth gravity," added Dr. Williams. "We plan to explore further what causes the spiral flame pattern, and what causes the tips to follow a [chaotic] meandering path."
Left: At NASA's Johnson Space Center, there is a microgravity research aircraft nicknamed the "Vomit Comet" used to fly parabolas to investigate the effects of "zero" gravity. The KC-135, typically used by the USAF for aerial refueling, is the military version of the venerable Boeing 707airliner.
Nayagam says it's an advantage to be able to generate these
flames in the lab under normal gravity, where it is easier and
less expensive to study them than on the Space Shuttle. The investigators
plan to conduct further tests with spiral flames on board the
Johnson Space Flight Center's KC-135, which can create brief
microgravity conditions in parabolic flight.
Why Set A Spinning Disk On Fire?
There are many spiral forms in nature, both on Earth and in space. Spirals occur in physical forms such as DNA and the shell formation of mollusks such as the conch and chambered nautilus. They also occur in wind patterns, including hurricanes and tornadoes. They are present in air and flame forms known as vortexes and whorls. And they occur in the way things fall in the atmosphere, from leaves to aircraft. In the human body, the spiral pattern of the heart's bioelectric impulses causes the chambers to beat with a spiral pulsing rhythm. Brain waves, comprised of neuron impulses, seem to flow along the neurons and down the spinal cord in a spiral pattern. Some evidence shows bioelectrical spiraling in the labor impulses during birth. Finally, we see spiral forms omnipresent throughout the visible and invisible universe, in galaxies, accretion disks around black holes, coalescing interstellar clouds and many other forms of matter and energy.
"Understanding these surprising phenomenon may enable
scientists to predict flame extinction and to help mitigate fire
risks on Earth and in microgravity," states Dr. Nayagam.
"The initial and on-going basic reason for NASA's combustion
studies is to learn about spacecraft fire safety. We need to
answer questions such as: what is the worst condition for fire
in a microgravity environment, and under what conditions a fire
will increase its burn rate or be extinguished. Our goals include
learning under what conditions materials in a spacecraft will
or won't support fire."
"The bottom line," Dr. Nayagam says, "is that this simple system of flames on a spinning disk under variable controlled conditions illustrates more complex systems on Earth, in spacecraft, and in the human body."
Readers can learn more about flames in space at the Microgravity Combustion Research home page.Web Links
Spiral Edge Flames in von Karman Swirling Flows -- by V.
Nayagam and F. A. Williams. Physical Review Letters -- January
17, 2000 -- Volume 84, Issue 3, pp. 479-482
Micro-fireballs Lighting the Way to Better Engine Designs-- 1997 Science@NASA headline story
Fires in Space - basic information
about combustion in low gravity from microgravity.com
Microgravity Research Program Office -- an overview of NASA's microgravity research, hosted by the NASA Marshall Space Flight Center
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