Heat Flux Determination in the High-Enthalpy Shock Tunnel Göttingen Using the Temperature-Sensitive Paint Method

Abstract

Already, aerospace engineers have to deal with the effects of hypersonic flow: intercontinental rockets, re-entry bodies and in the future hypersonic airplanes, too. A hypersonic flow leads to strong compression waves and thus high temperatures and great heat fluxes into the spacecraft. Dealing with these heat fluxes is a central requirement for engineers, who construct hypersonic vehicles. Furthermore, this task becomes much harder, because the experimental simulation of hypersonic flows is possible just with high efforts. The Department Spacecraft of the Institute of Aerodynamics and Flow technology of the German Aerospace Center (DLR) operates the High-enthalpy Shock Tunnel Göttingen (HEG) to solve this problem. It is one of the greatest European hypersonic facilities to simulate flows with reacting gases. The measurement time in this facility is limited due to its technical structure. Typical measurement times are in the range of a few milliseconds. Therefore, measurement technology to determine surface heat flux densities has to be optimized in terms of measurement speed; which means acquisition rates between 10 and 100 kHz have to be realized. Furthermore, the requirements in measurement precision and temporal and spatial resolution are very high. To determine the surface heat flux density, the development of temperature-sensitive paints (TSP) is in progress at the department. TSP is an imaging temperature measurement technique. Its benefits compared to the already used Infrared thermography are the higher spatial resolution and the lower technical effort: neither special cameras nor tunnel windows are needed. On the other hand, the Infrared thermography can detect smaller temperature differences, and the TSP method needs additional equipment: the paint layer, the excitation light sources and the color filter. In the framework of this master thesis, reference experiments to proof the practicability of the TSP method for measurements in the HEG shall be performed. This contains the calibration of the used camera, the proof of the reproducibility of the pre-tests using the shock tube of the DLR Göttingen, the calibration of the paint and the study of its behavior under the conditions of measurements at the HEG. These are primarily the very short measurement time, an unsteady flow and strong temperature gradients. At the end, the quality of the method shall be quantified in terms of temperature sensitivity as well as spatial and temporal resolution