Radiance measurements through unsteady expansion waves in relaxing air and H2-He mixtures

Conference item

Impulse facilities, such as shock tubes and expansion tubes, serve as crucial tools for interrogation of the thermochemical processes occurring in the shock layer surrounding hypersonic vehicles. Measurements made in these facilities are used to deduce reaction rate coefficients for chemical-kinetic models that are ultimately used for vehicle design. Expansion tubes leverage an unsteady expansion flow process to achieve large total enthalpies. This has been shown to lead to thermochemical freezing of the freestream in some cases, a fact that drives uncertainty in results obtained from these facilities. Integrated radiance measurements of the oxygen 777 nm and hydrogen 656 nm atomic lines have been made at several points downstream of the secondary diaphragm of the T6 Stalker tunnel in expansion tube mode. A radiometer probe design suitable for use in the tube wall was developed and validated against measurements made via optical emission spectroscopy. Measurements made downstream of the secondary diaphragm clearly visualise the unsteady expansion and indicate a test time that is in agreement with pressure measurements. Absolute radiance values during the test time are higher than those predicted by equilibrium, state-to-state analysis, indicating the need for improved modelling tools for expansion tube flows.

Authors: Steer, J; Collen, P; McGilvray, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Institute of Aeronautics and Astronautics
• Host title: AIAA Aviation Forum and ASCEND co-located Conference Proceedings
• Article number: 3652
• Publication date: 2024-07-27
• Acceptance date: 2024-03-18
• Event title: AIAA Aviation Forum and ASCEND, 2024
• Event location: Las Vegas, Nevada, USA
• Event website: https://aiaa.org/wp-content/uploads/2025/01/2024-avas-recapweb0c642fb0574e4e87bf4dbab982a0fd4d.pdf
• Event start date: 2024-07-29
• Event end date: 2024-08-02
• DOI: 10.2514/6.2024-3652
• Language: English
• Keywords: fluid mechanics; radiative heating; freestream conditions; hypersonic shock; optical emission spectroscopy; enthalpy; hypersonic vehicles; pressure transducers; transmittance; spectrometers