Disintegration of large meteoroids, 1 m to 1 km in size, when affected by aerodynamic forces in flight is considered in this paper. Arguments are adduced that ablation is of secondary importance in comparison with mechanical processes of deformation and fragmentation. 2D hydrodynamic simulations using the free-Lagrangian method and the Eulerian method with a volume-of-fluid front tracking procedure have been carried out. The cosmic body was treated as a fluid, with the equation of state of water, moving through gas of appropriate density. We find that disintegration is more complex than simple models based on the estimate of lateral expansion due to differential ram pressure across a meteoroid make it. Rayleigh-Taylor instabilities strongly deform the body and it breaks up in the center. The outer radius of an originally spherical or cylindrical body agrees with the analytic models of spreading. However, a body of accidentally aerodynamic shape does not have its cross section significantly enlarged. A sandbag model has been developed in which a heavily dispersed meteoroid is represented as a conglomeration of noncolliding particles moving through the atmosphere. The particles transfer energy and impulse to the atmosphere and are enclosed by a single bow shock. Calculations show that a spherical swarm of particles takes a conical form but lateral expansion agrees with the above-mentioned simple theoretical models. The approximate analytical approach of a spreading fragmented impactor has got additional support: integration of the drag, ablation, and radiation equations produces results which are in a good agreement with light flashes registered by DoD satellites. (C) 1995 Academic Press, Inc.
