http://science.nasa.gov/science-news/science-at-nasa/2000/ast12may_1/ wrote:
Not Just Another Old Flame
NASA scientists have discovered unexpected spiral-shaped flames on Earth.
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. "The tall spear-shaped flame on a candle, or the "roaring hearth" look of bonfire-type flames, or the forced-air look of a rocket or furnace flame are very different indeed in the absence of gravity," Dr. Nayagam states. "Soot production, burning rates, completeness of combustion, exhaust products and other characteristics all change radically in space. "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."
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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.
Nayagam and Williams ignited a plastic disk a little bigger than a CD with a blowtorch and then spun it slowly (2 to 20 revolutions per second) in still air. They expected to see flames burning as a horizontal disk. Instead, the flame burned in a flat spiral pattern, with the spiral moving in the direction opposite to the disk's spin. As the flames lessened their tips exhibited a strange meandering motion from side to side.
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."
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.
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Why Set A Spinning Disk On Fire? (Spirals, Spirals, everywhere....)
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.
"We need to discover how and why flames propagate in microgravity, and under what conditions flame propagation changes. Hopefully the studies will also explain turbulent combustion, as the swirling flow is vital to understanding the phenomenon called fire whorl," says Dr. Nayagam.
"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."
Flame Nebula Close Up
