Numerical Simulation of Unstart Processes in an Axisymmetric Scramjet Combustor

Caleb A. Hash, Paige M. Drummond, Jack R. Edwards, Nozomu Kato, Tonghun Lee

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Large-eddy simulations of stable and unstable ramjet operational modes are presented for an axisymmetric inlet-isolator-combustor configuration experimentally tested in the University of Illinois’s ACT-II arc-heated combustion tunnel. A 32 species ethylene oxidation mechanism including nitrous oxide formation reactions is used in the calculations. Conjugate heat-transfer models based on an assumed penetration depth of the applied heating load are used to account for localized wall heating during the short durations (~0.2 to 0.3 s) of the parts of the experiments simulated in this work. The results show a marked sensitivity to trace levels of atomic oxygen (~1% by mass) in the free stream – these trace levels are a consequence of the arc-heating process at ~1 bar pressure and the use of baffles to enhance mixing of oxygen with arc-heated nitrogen. With 1% atomic oxygen in the free stream, a jet-wake stabilized, partially-premixed flame structure emerges during thermal-throat ramjet operation at an equivalence ratio of 1.24, in accord with available experimental pressure and imaging measurements. Simulations of unstable ram-mode operation leading to inlet unstart at an equivalence ratio of 1.97 indicate a sensitivity to the thermal-wall boundary condition, the ignition method, and the free-stream composition. A reduction in atomic oxygen concentration to 0.8% by mass yields good agreement with the experimentally-observed shock-train propagation speed. Both the computational and experimental results indicate that the shock train accelerates before being disgorged from the inlet. This acceleration stems from a rapid increase in the sizes of regions of low speed, sometimes separated flow behind Mach disks that form as the shock train proceeds upstream.

Original languageEnglish (US)
Title of host publicationAIAA SciTech Forum 2022
PublisherAmerican Institute of Aeronautics and Astronautics Inc, AIAA
ISBN (Print)9781624106316
StatePublished - 2022
EventAIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022 - San Diego, United States
Duration: Jan 3 2022Jan 7 2022

Publication series

NameAIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022


ConferenceAIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022
Country/TerritoryUnited States
CitySan Diego

ASJC Scopus subject areas

  • Aerospace Engineering


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