Calibration of Fast-Response Temperature Sensitive Paints for Their Application in Hypersonic High Enthalpy Flows

For a spacecraft traveling at hypersonic speeds, the design of the vehicle’s thermal protection system is crucial [2] and the accurate quantification of the surface heat flux is mandatory to aid this design. Traditional surface-mounted temperature sensors, such as thermocouples and thin film gauges, have been widely used as reported already over 40 years ago by [19]. These sensors have response times on the order of a few microseconds, and thus data can be sampled with high temporal resolution; typically 1 MHz. However, the spatial resolution is less satisfactory: the packing density is limited by the sensor size and a great amount of expertise is needed to mount sensors on narrow geometries (e.g. sharp leading edges or corners). In addition, the installation of large numbers of transducers results in complicated wiring and high costs. The clear advantages of temperature sensitive paints (TSPs) over the classical techniques are the non-intrusive measurement approach and the high spatial resolution. A feasibility application of fast-response TSPs in Europe’s major hypersonic facility, the High Enthalpy Shock Tunnel Göttingen (HEG), on transition measurements has already been published [18]. These measurements demonstrated the ability of the TSP method to be used for measurements of time resolved surface temperatures and consequently the determination of surface heat fluxes; the TSP used in the publication was based on the luminophore Ru(phen). This paper will discuss the prerequisites, the requirements and the calibration work which has to be accomplished to progress the development of ultra-fast temperature sensitive paints towards a more versatile application in hypersonic high enthalpy flows in the HEG. Additional information on the HEG is reported by Hannemann and Martinez Schramm [7]. The calibration procedure is shown for the laser dye 4-Methylumbelliferone (4MU) which has been determined to be the next promising candidate for the application in the HEG [15].