Speaker
Description
Background
The development of re-entry 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 re-entry 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 re-entry-relevant freestream conditions.
Methodology
A flat-faced cylindrical probe to generate a bow shock layer upstream of the model face has been designed and implemented in the HEG. 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.
Results
Results will be presented for surface sensors on the probe, indicating the establishment of the shock layer and the detection of total and radiative heat flux components. The latter was recorded for different wavelength bands and comparisons will be drawn from measurements made in the UV-VIS to the NIR regions. Results from the in-situ OES will be used to assess the presence of contaminant species and mass spectrometry result will assist in ascertaining the possible source of these contaminants.
Conclusion
A flat-faced cylindrical probe has been successfully implemented in the HEG and first results of its usage will be presented. A workflow combining in-situ OES and mass spectrometry has resulted in increased certainty in identifying sources of contaminant species in high-enthalpy hypersonic radiative flows.
References
[1] H. Tanno, T. Komuro, R.P.Lillard und J. Olejniczak, „Experimental study of high-enthalpy heat flux augmentation in shock tunnels,“ Journal of Thermophysics and Heat Transfer, pp. 858-862, Oct - Dec 2015.
[2] B. Cruden, C. Tang, J. Olejniczak, A. Amar und H. Tanno, „Characterization of radiative heating anomaly in high enthalpy shock tunnels,“ Experiments in Fluids, 2021.
[3] B. Hollis und D. Prabhu, „Assessment if laminar, convective aeroheating uncertainties for Mars-entry vehicles,“ Journal of Spacecraft and Rockets, pp. 56 - 68, Jan - Feb 2013.
[4] E. Marineau, D. Lewis, M. Smith, J. Lafferty, M. White und A. Amar, „Investigation of hypersonic laminar heating augmentation in the stagnation region,“ presented at the 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Jan 2013.
[5] J. M. Schramm, A. Wagner, D. Surujhlal, G. Camillo und T. Ecker, „The High Enthalpy Shock Tunnel Göttingen of the German Aerospace Center (DLR),“ Journal of Large-Scale Research Facilities, in print, 2024.
Summary
A flat-faced cylindrical probe has been successfully implemented in the HEG and first results of its usage will be presented. A workflow combining in-situ emission spectrometry and mass spectrometry has resulted in increased certainty in identifying sources of contaminant species in high-enthalpy hypersonic radiative flows.
