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Aeronautical and Astronautical Engineering
Combustion
- Effects of Nonuniform Flows on Propellant Flames
- Holes in Diffusion Flames
- Oscillating Edge Flames
- Sublimit Combustion and Flame Strings
- The Effects of Convective Flows on Premixed Edge-Flames
- Two-dimensional Smolder Waves
^ Effects of Nonuniform Flows on Propellant Flames
J. Buckmaster*
U.S. Air Force Office of Scientific Research, F49620-96-1-0031; DOE Center for Simulation of Advanced Rockets
Researchers are examining propellant flames supported by heterogeneous propellants in which time-periodic nonuniform flows are applied to simulate the effect of acoustic and turbulent disturbances in the rocket flow. These flows distort the flame structure, affect the mixing, and have a substantial influence on the heat flux to the propellant surface. This, in turn, affects the propellant regression rate.
^ Holes in Diffusion Flames
J. Buckmaster,* T. L. Jackson (CSAR)
U.S. Air Force Office of Scientific Research, F49620-96-1-0031
In turbulent nonpremixed combustion, eddies can tear holes in the flame. The subsequent history of these holes (whether they close or get larger) is important in any understanding of the combustion field. Researchers have devised a model to examine holes and their propensity to close or open. A closely related problem is that of a flame-isola, an isolated region of burning, and its propensity to expand or shrink.
^ Oscillating Edge Flames
J. Buckmaster,* Y. Zhang
U.S. Air Force Office of Scientific Research, F49620-96-1-0031; National Aeronautics and Space Administration, NAG 3-1704
The edge of a flame spreading over liquid fuel beds at subflash temperatures will sometimes pulsate. Similar pulsations are seen in a candle flame burning under microgravity conditions. An edge flame model has been developed to study this phenomenon, which researchers believe is a Lewis number effect.
^ Sublimit Combustion and Flame Strings
J. Buckmaster,* M. Short (Theoret. & Appl. Mech.)
U.S. Air Force Office of Scientific Research, F49620-96-1-0031; National Aeronautics and Space Administration, NAG 3-1704
Edge flames are constructed by cutting a flame placed in a premixed fresh/fresh counterflow of reactants to form semi-infinite flame sheets. The edge of these sheets propagates in a wave-like fashion and defines the edge flame. When the Lewis number of the deficient reactant is small, the flame structure behind the edge is unstable and breaks up into flame strings, cylindrical flames that have been observed in microgravity experiments. The strings can survive straining rates that quench a one-dimensional flame and are sublimit structures.
^ The Effects of Convective Flows on Premixed Edge-Flames
J. Buckmaster,*
U.S. Air Force Office of Scientific Research, F49620-96-1-0031
A simple edge-flame model is examined for which the underlying one-dimensional system defines a deflagration. It is shown that edge oscillations can be induced by the imposition of an on-edge convective flow. On the other hand, imposition of an off-edge flow tends to suppress oscillations.
^ Two-dimensional Smolder Waves
J. Buckmaster,* Y. Zhang
U.S. Air Force Office of Scientific Research, F49620-96-1-0031
A great deal of work has been done on one-dimensional smolder waves in which the area of the smolder front is fixed. Researchers are concerned with what happens when smolder is initiated in a restricted domain so that not only does it have the opportunity to move forward, it has the opportunity to move sideways, enlarging the area of the smolder front. Calculations are designed to explain what controls the sideways spread and what can prevent it from occurring.
