Pii: S0301-9322(99)00043-9

The breakup of viscous and viscoelastic drops in the high speed airstream behind a shock wave in a shock tube was photographed with a rotating drum camera giving one photograph every 5 ms. From these photographs we created movies of the fragmentation history of viscous drops of widely varying viscosity, and viscoelastic drops, at very high Weber and Reynolds numbers. Drops of the order of one millimeter are reduced to droplet clouds and possibly to vapor in times less than 500 ms. The movies may be viewed at http://www.aem.umn.edu /research/Aerodynamic_Breakup. They reveal sequences of breakup events which were previously unavailable for study. Bag and bag-and-stamen breakup can be seen at very high Weber numbers, in the regime of breakup previously called `catastrophic'. The movies allow us to generate precise displacement±time graphs from which accurate values of acceleration (of orders 10 to 10 times the acceleration of gravity) are computed. These large accelerations from gas to liquid put the ̄attened drops at high risk to Rayleigh±Taylor instabilities. The most unstable Rayleigh± Taylor wave ®ts nearly perfectly with waves measured on enhanced images of drops from the movies, but the e€ects of viscosity cannot be neglected. Other features of drop breakup under extreme conditions, not treated here, are available on our Web site. # 1999 Elsevier Science Ltd. All rights reserved.