Overview of Boundary Layer Transition Research in Support of Orbiter Return to Flight

Abstract

A predictive tool for estimating the onset of boundary layer transition resulting from damage to and/or repair of the thermal protection system was developed in support of Shuttle Return to Flight. The boundary layer transition tool is part of a suite of tools that analyze the aerothermodynamic environment to the local thermal protection system to allow informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each damage site or repair, the expected time (and thus Mach number) at transition onset is predicted to help define the aerothermodynamic environment to use in the subsequent thermal and stress analysis of the local thermal protection system and structure. The boundary layer transition criteria utilized for the tool was developed from ground-based measurements to account for the effect of both protuberances and cavities and has been calibrated against select flight data. Computed local boundary layer edge conditions were used to correlate the results, specifically the momentum thickness Reynolds number over the edge Mach number and the boundary layer thickness. For the initial Return to Flight mission, STS-114, empirical curve coefficients of 27, 100, and 900 were selected to predict transition onset for protuberances based on height, and cavities based on depth and length, respectively.

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

“…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. This empirical methodology, adopted to quickly assess thermal environments induced by damage to the Shuttle's TPS, is derived from ground-based measurements 16,17 that are extrapolated to flight using representative (and limited) flight data 18 . During the RTF BLT predictive tool development phase, it was recognized that the level of conservatism imposed by these extrapolation uncertainties could be more clearly established and/or reduced with quality data from a controlled roughness flight experiment.…”

Infrared Imaging of Boundary Layer Transition Flight Experiments

“…1 This effort resulted in a mission support tool that is integral to the damage assessment process for Orbiter TPS health monitoring, which has been used during every mission since the Columbia accident. The BLT Tool predicts transition onset time during entry for both protuberances and cavities, based on the ground-based developed correlations that were calibrated against a limited set of historical flight transition data.…”

Cast Glance Near Infrared Imaging Observations of the Space Shuttle During Hypersonic Re-entry

“…The renewed interest in thermal imagery during Shuttle re-entry was initially motivated by the desire to reduce uncertainties associated with an empirical strategy to predict BLT onset. This empirical methodology, adopted to quickly assess thermal environments induced by damage to the Shuttle's TPS, is derived from ground-based measurements 16,17 that are extrapolated to flight using representative (and limited) flight data 18 . During the RTF, BLT predictive tool development phase, it was recognized that the level of conservatism imposed by these extrapolation uncertainties could be more clearly established and/or reduced with quality data from a controlled roughness flight experiment.…”