Breakup of a liquid drop suddenly exposed to a high-speed airstream

The breakup of viscous and viscoelastic drops in the high speed airstream b ehind a shock wave in a shock tube was photographed with a rotating drum ca mera giving one photograph every 5 mu s. From these photographs we created movies of the fragmentation history of viscous drops of widely varying visc osity, and viscoelastic drops, at very high Weber and Reynolds numbers. Dro ps of the order of one millimeter are reduced to droplet clouds and possibl y to vapor in times less than 500 mu s. The movies may be viewed at http:// www.aem.umn.edu/research/Aerodynamic_Breakup. They reveal sequences of brea kup events which were previously unavailable for study. Bag and bag-and-sta men breakup can be seen at very high Weber numbers, in the regime of breaku p previously called 'catastrophic'. The movies allow us to generate precise displacement-time graphs from which accurate values of acceleration (of or ders 10(4) to 10(5) times the acceleration of gravity) are computed. These large accelerations from gas to liquid put the flattened drops at high risk to Rayleigh-Taylor instabilities, The most unstable Rayleigh-Taylor wave f its nearly perfectly with waves measured on enhanced images of drops from t he movies, but the effects of viscosity cannot be neglected. Other features of drop breakup under extreme conditions, not treated here, are available on our Web site. (C) 1999 Elsevier Science Ltd. All rights reserved.