Heat flux augmentation in high-enthalpy flows

Abstract

The development of reentry aerodynamic configurations requires examination of the flow around a re-entry body. Re-entry relevant freestream conditions are suitably generated by shock tunnels such as the High Enthalpy Shock Tunnel Göttingen (HEG). This large-scale facility was commissioned in 1990 at the German Aerospace Center (DLR) and is one of Europe’s premier tunnels for the examination of re-entry aerothermodynamics at flight-representative conditions. A common problem faced by flight vehicle re-entry is the bow shock formed ahead of the vehicle. For such a model placed in the freestream of a shock tunnel, this results in re-stagnation of the freestream flow causing extremely high temperatures and pressures, and partial dissociation of the test gas in this region. This region is therefore of interest for obtaining surface pressure and heat flux measurements for re-entry vehicle structural design and thermal protection. Recent measurements in high-energy flows similar to HEG have shown surface heat flux on re-entry capsules to significantly exceed that predicted by numerical simulations and models. This seemingly anomalous result has become known as heating augmentation and was hypothesised to be due to radiation of flow species through the bow shock formed ahead of the capsule. Furthermore, previous observations made at the HEG of stagnation point flows have demonstrated fluctuations within the radiating shock layer. The main objective of the research project and upcoming experiments is to probe the shock layer and thereby investigate the fluctuations of radiation heat flux in the shock layer.