Development and Application of Phosphor-Based Temperature Sensitive Paint on a Heated Model in HEG

Kurzfassung

Predictions of surface heating in hypersonic flight is crucial for the structural and thermal protection system design and influences the overall flight vehicle performance. The aerothermal loading of flight relevant configuration under representative flight conditions can be simulated in shock tunnels, one of which is the High Enthalpy Shock Tunnel Göttingen (HEG) at the German Aerospace Center (DLR). The HEG, a free-piston-driven shock tunnel, produces flow velocities between 2 km/s to 6 km/s as well as high total gas temperatures up to 10000 K at typical test times of approximately 5 ms. Due to the short test times, the absolute temperature increase of the test models is limited. The used models are tested being thermally cold, which restricts the representation of a realistic wall-to stagnation temperature ratio that is an important influence factor on flow field topologies in comparison to flight. In order to simulate more realistic surface temperatures encountered during re-entry or flight, artificial heating of models is required. Such a test model with additional heating infrastructure was manufactured for tests in HEG. The hollow cylinder model with variable segments allows heating up to 800 K and thus enables investigations under more realistic flight conditions at HEG. In consequence, suitable measurement techniques for acquisition of spatiotemporally resolved temperature data on these heated model surfaces are required. Temperature sensitive paint (TSP) has established itself as reliable technique for heat flux analysis with high spatial resolution. The technique uses the change in luminescence from a thin layer of luminescent molecules deposited on the model surface to measure the surface temperature. The Spacecraft Department at DLR has advanced the TSP technique using organic luminophores adapted to the ultra-fast response times needed for application at impulse facilities such as the HEG. Since the organic luminophores undergo chemical degradation and exhibit strong thermal quenching at temperatures above 100°C, novel TSP formulations based on inorganic compounds are necessary to extend the operational range for testing at elevated surface temperatures, while preserving short luminescent lifetimes, good surface adhesion and robustness, and sufficient signal intensity. This resulted in the development of a high-temperature TSP (H-TSP) based on an Europium-doped phosphor ((Ca,Sr)AlSiN3:Eu2+), that is suspended in an inorganic high-temperature silicon resin. The static calibration of this novel H-TSP mixture was performed in a calibration chamber to determine the operational range and the dependency of intensity decrease with respect to increasing surface temperature. Following this calibration, the H-TSP was commissioned for use on the heated test model in HEG. Details on the calibration will be discussed in the presentation. Preliminary results will be presented on the first use of this H-TSP in HEG for wall temperatures up to 600 K.