Radiation of contaminant species in the High Enthalpy Shock Tunnel Göttingen (HEG)

The development of reentry aerodynamic configurations requires examination of surface heat flux. Surface heating due to radiation at high-enthalpy stagnation conditions has been shown to comprise a significant portion of the total measured surface heat flux on reentry configurations [1] [2]. Earlier studies in high-enthalpy flows on blunt sphere-cones [3] and capsules [4] indicated substantially increased surface heat flux levels at or near the stagnation region than predicted numerically. This presents difficulties with numerical reconstruction of such test cases, and also regarding formulation of experiments serving as validation cases. It has been hypothesised that the extra heating component measured was due to radiation of contaminant species, in addition to flow species, within the shock layer [1]. This was termed radiation augmentation, the source of which is currently unclear. Systematic investigation of this would benefit from further tests under conditions of the High Enthalpy Shock Tunnel (HEG) [5], which can reproduce a variety of reentry-relevant freestream conditions. In our previous submission, the design of a flat-faced cylindrical probe to generate a bow shock layer upstream of the model face was described. The probe houses an array of surface-mounted sensors including a radiative heat flux sensor, pressure sensors, temperature sensors, and fibre optic components for in-situ optical emission spectroscopic (OES) measurements within the shock layer. This work will focus on the in-situ OES measurements, which were made at up to 4 kHz and with different line-of-sight orientations. Furthermore, the use of a mass spectrometer and a scanning electron microscope enabled investigation of contaminants obtained post-test from the HEG tunnel walls and assisted in understanding possible sources of contaminant species. The HEG was used at various reservoir conditions (low- and high-enthalpies) up to a reservoir pressure of 44 MPa and a specific reservoir enthalpy of 12 MJ/kg.