The problem addressed in this research program is to understand the dissemination of Newtonian and non-Newtonian liquids which are exposed to a supersonic air stream (Mach numbers up to about 6) at high altitudes. It is known that a mass of Newtonian liquid is reduced to a droplet cloud in hundreds of microseconds, and it is believed that considerable amounts of vapor or mist are produced. However, little is known about the breakup of viscoelastic liquids, as for example the distribution of drop sizes, the volume fractions of mist and vapor, and the precise influence of non-Newtonian effects on the breakup mechanism and on the droplet distribution. The objectives of this program are to use carefully controlled experiments to analyze the breakup mechanics and the resulting droplet clouds, and thereby to obtain precise information about the formation of droplet clouds under conditions met in high speed and high altitude breakup. It is anticipated that controlled studies of this type will provide information on droplet sizes at times of the order of 10 to 1,000 microseconds after impact under a variety of ambient conditions.
These experiments will reveal what mechanisms are at work during breakup, and are important because there is a great difference between the breakup of organic liquids (solvents) and thickened liquids (solvent plus polymers). Organic liquids shatter into small drops and mist at high Mach numbers, but the breakup of viscoelastic liquids under similar conditions may occur through the liquid being pulled into threads as well as droplets. It is important to see if and how these threads persist in the severe conditions behind a strong shock. Breakup studies of both Newtonian and non-Newtonian liquids are being carried out in our shock tube facility at shock Mach numbers in the range 1.5 to 5.
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