The flames surrounding a burning tree stump flicker and billow in this image from photographer Serdar Ozturk. The chaotic motion of the flames is indicative of turbulence, a state of fluid flow known for its many scales. Note the range of lengthscales and structures in the fire. In turbulent flows, kinetic energy cascades from large scales, like the width of the top of the plume, down to the small scales, which may be even smaller than the wisps of flame at the edges of the fire. At the largest scales, the structures and behaviors we observe are all flow- and geometry-dependent, but theory predicts that, at the smallest scales, all turbulent flows look the same. (Photo credit: trashhand/Serdar Ozturk)
Tag: fire
Flame Thrower Physics
This high-speed video–which we do not recommend recreating yourself–features burning gasoline flying through the air. In addition to the sheer entertainment value, there are some neat physics. In the first segment, when they kick a tray of gasoline, one can see lovely fiery vortices forming around the backside of the tray as it’s launched. This is the start of the tray’s wake. In the latter half of the video, they launch the flaming gasoline from a bucket. Notice how the flames are in the wake while liquid gasoline streams out ahead without burning. This is because it is primarily gaseous petrol that is flammable. As the liquid fuel breaks up into droplets heated by the burning gasoline vapors nearby, the rest of the fuel changes to a vapor state and catches flame. (Video credit: The Slow Mo Guys; submitted by Will T)
Fire Tornado
An artificial fire tornado makes for fascinating viewing. The box fans are positioned around a central firepit such that they impart the angular velocity needed to create a vortex. I’ve actually seen an even bigger live demonstration than this one at a fluid dynamics conference. Do not try this yourself. Fire tornadoes occur in nature, too: take a look at how they form. (submitted by acervant)
Diesel Ignition
In a diesel engine, ignition of the injected fuel occurs due to the heat caused by the compression of the fuel/air mixture. (In petrol/gasoline engines, spark plugs are used for ignition.) The subsequent expansion of gases drives the pistons of the engine downward, creating mechanical energy. This high-speed video shows the in-cylinder combustion within a diesel engine. Note the symmetry and vorticity of the flow.
