Infrared Imaging of Boundary Layer Transition Flight Experiments

Abstract

The Hypersonic Thermodynamic Infrared Measurement (HYTHIRM) project is presently focused on near term support to the Shuttle program through the development of an infrared imaging capability of sufficient spatial and temporal resolution to augment existing on-board Orbiter instrumentation. Significant progress has been made with the identification and inventory of relevant existing optical imaging assets and the development, maturation, and validation of simulation and modeling tools for assessment and mission planning purposes, which were intended to lead to the best strategies and assets for successful acquisition of quantitative global surface temperature data on the Shuttle during entry. However, there are longer-term goals of providing global infrared imaging support to other flight projects as well. A status of HYTHIRM from the perspective of how two NASAsponsored boundary layer transition flight experiments could benefit by infrared measurements is provided. Those two flight projects are the Hypersonic Boundary layer Transition (HyBoLT) flight experiment and the Shuttle Boundary Layer Transition Flight Experiment (BLT FE), which are both intended for reducing uncertainties associated with the extrapolation of wind tunnel derived transition correlations for flight application. Thus, the criticality of obtaining high quality flight data along with the impact it would provide to the Shuttle program damage assessment process are discussed. Two recent wind tunnel efforts that were intended as risk mitigation in terms of quantifying the transition process and resulting turbulent wedge locations are briefly reviewed. Progress is being made towards finalizing an imaging strategy in support of the Shuttle BLT FE, however there are no plans currently to image HyBoLT.

The Hythirm Project: Flight Thermography of the Space Shuttle During Hypersonic Re-Entry

“…Quantitatively, if surface temperatures associated with a hypersonic laminar and/or fully turbulent boundary layer flow can be inferred from calibrated in flight imagery, they could be used to verify engineering models or numerical predictive methods and associated turbulence models. While most aerospace applications of infrared thermography have been limited to wind tunnel testing, this measurement technique has been utilized during several Shuttle entries over the past 25 years to obtain flight data [6][7][8][9][10][11][12][13][14][15] . The renewed interest in thermal imagery during Shuttle entry was initially motivated by the desire to reduce uncertainties associated with an empirical strategy to predict BLT onset.…”

Application of a Near Infrared Imaging System for Thermographic Imaging of the Space Shuttle during Hypersonic Re-Entry

“…This paper will provide the motivation and details behind the use of a digital NIR imaging system and describe the characterizations and procedure performed to obtain quantitative temperature imagery. Past attempts by the Cast Glance aircraft to image the Space Shuttle during STS-121 and STS-115 missions has resulted in successful image captures, however the quality of the acquired data allowed for limited data processing 4,5,6,7 . During both missions, the Shuttle imagery was obtained using an analog based NIR imaging system, however due to image saturation, limited quantitative analysis could be performed.…”

Assessment and Mission Planning Capability for Quantitative Aerothermodynamic Flight Measurements Using Remote Imaging

“…15, the Mach 6 perfect gas test qualitatively revealed that the turbulent wedge angle as inferred from the wind tunnel image in Fig. 12 was slightly smaller and directed more inboard than expected at Mach 18 flight conditions.…”

“…See Ref. 15 for further discussion on the observed turbulent wedge insensitivity to Shuttle angle-of-attack and sideslip.…”

“…Formal requirements will evolve from the final NESC trade study report. While the final HYTHIRM trade study has not been issued, flexibility appears to be the best strategy from which to ensure a higher probability of obtaining quantitative imagery 12,15 . A clear understanding of strengths and weaknesses of airborne and land-based systems is essential to successful mission support.…”