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Limitations on the Applicability of High-Explosive Charges for Simulating Nuclear Airblast

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Memorandum rept.

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Since flow fields that result from nuclear and high explosive HE detonations are qualitatively alike but quantitatively different, care must be exercised in carrying over conclusions drawn from measurements of HE tests to nuclear explosions. The usefulness of HE explosions for simulating nuclear airblast is predicted on the fact that after reaching 5-6 times the initial radius, the flow field looks like that produced by a point source and produces shock overpressures similar to those in the nuclear case. Numerical simulations of airblast phenomena have been carried out using one- and two-fluid Flux- Corrected Transport hydrodycodes in one and two dimensions. The principal difference in the free-field solutions are the presence in the HE case of contact discontinuity between air and HE products and of a backward-facing shock behind it. Temperatures in the nuclear fireball are initially three orders of magnitude higher correspondingly, the density minimum at the center of the fireball is much broader and deeper. When the blast in a nuclear height-of-burst HOB situation undergoes regular reflections from the ground only one peak develops in the overpressure, and the reflected wave propagates upward rapidly through the hot underdense fireball. In the HE case part of the upward-moving reflected wave is reflected downward at the contact surface, producing a second pressure peak on the ground, while the shock transmitted through the contact surface propagates slowly upward. After transition to Mach reflection other differences appear. At late times following shock breakaway the nuclear fireball, unlike the HE fireball, appears to develop a Rayleigh-Taylor instability along its lower edge below the HOB.

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  • Explosions
  • Fluid Mechanics

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