Characterization of Expansion Tube Flows for Hypervelocity Combustion Studies

An expansion tube with an 89 mm inner diameter and a 12 m length was characterized for basic studies of the near-e eld mixing and e ame-holding characteristics of gaseous fuels injected in high-stagnation-enthalpy supersonic e ows. The expansion tube provides a wide range of freestream conditions with little perturbation of test gas chemical composition. The latter is critical for supersonic-combustion studies in the high-stagnationenthalpy e ows associated with hypersonic airbreathing propulsion systems. Efforts focused on achieving three operatingpoints,simulatinge ightMach8,10,and12stagnation-enthalpyconditionsattheentranceofasupersonic combustor. The ability of the expansion tube to provide a steady-e ow test time of adequate duration and a core e ow of sufe cient size for 2-mm jet-in-crosse ow studies was verie ed. A core-e ow size of 25 mm could be achieved in 6.2 MJ/kg stagnation-enthalpy e ows with 400 πs of steady test time (e ight Mach 12 simulation ). The primary effects of the boundary layer on the expansion tube e ow were to extend the useful test time (in contrast with conventional shock-tube performance ) and to decrease the core-e ow size.