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Regime diagram for droplet breakup and phase transition in shock-driven and detonative flows

Lorenzo Angelilli* and Venkat Raman

  • *Contact author: langelil@umich.edu
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Phys. Rev. Fluids 11, 100501 – Published 7 October, 2026

DOI: https://doi.org/10.1103/cljr-373d

Abstract

Liquid-fueled detonative flows involve heavily coupled droplet breakup, phase transition, and chemical heat release over extremely short timescales. In rotating detonation engines and related high-speed propulsion systems, whether liquid fuel remains coupled to the leading wave depends not only on droplet size or Weber number, but also on the total work extractable imposed by the compressible flow and the timescale over which vapor becomes available. This work develops a regime diagram for droplet dynamics in shock-driven and detonative environments using two dimensionless groups: a thermodynamic-load coordinate, which measures the ability of the surrounding gas to drive droplet disintegration, and a timescale ratio, which compares phase-change and aerodynamic-response rates. The diagram is constructed using physically based criteria for aerodynamic breakup, compressibility effects, and transcritical or supercritical interfacial behavior. Recent shock-droplet interaction experiments, liquid-fueled detonation studies, and rotating detonation engine data are mapped onto this framework. The resulting classification shows that water droplets generally remain in breakup-dominated regimes, whereas hydrocarbon fuels more readily enter compressible and supercritical-transition regimes where rapid vapor release can couple with detonation heat release. For liquid-fueled rotating detonations, sustained operation is favored when strong thermodynamic loading is combined with phase-change rates fast enough to synchronize vapor production with the wave cycle. The diagram provides a unified interpretation of breakup, vaporization, and sustained two-phase detonation, while highlighting the need for phase-change models valid across all the possible thermodynamic conditions.

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Phys. Rev. Fluids 11, 100501– Published 7 October, 2026
  • Received 1 June 2026
  • Accepted 8 September 2026
Article part of CHORUS
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