Simulation of CO2-N2 Expansion Tunnel Flows for the Study of Radiating Shock Layers

A 25MJ/kg CO2–N2 expansion tunnel condition has been developed for the study of radiating shock layers in the X2 impulse facility at the University of Queensland. A hybrid Lagrangian and Navier–Stokes computational simulation technique is found to give good correlation with experimentally measured shock speeds and pressure traces. The use of a decaying inertial diaphragm model for describing secondary diaphragm rupture is found to predict between 4% and 25% more CO2 recombination over the test time than the widely accepted holding-time model. Inviscid simulations of the hypersonic nozzle expansion process with a two-temperature model indicate the final test gas is in both chemical and thermal nonequilibrium. The obtained freestream conditions are applied to radiatively coupled simulations of a 25mm diameter cylinder in the test flow. Grid independent solutions show good agreement with experimentally measured shock detachment and predict a radiative emission spectrum dominated by the CO Fourth-Postive band system.

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