Aerothermodynamic Design of Space Vehicles: Experiment and CFD

Kurzfassung

Aerothermodynamics is aimed at determining forces, moments and thermal loads of a spacecraft being launched or returning from orbit. The right shape as well as accurate prediction of the thermal loads determines the selection and dimensioning of thermal protection systems and load carrying structures, the guidance navigation and control of the vehicle as well as numerous mechanical and electrical subsystems. Therefore, aerothermodynamics represents a key technology for the development of space transportation systems. The aerothermodynamic behaviour of space transportation systems needs to be verified by computations using advanced numerical tools, experimental investigations in ground based experimental facilities and by flight tests and is essential for the optimization of aerodynamic shapes. The aerothermodynamics team of DLR was involved during the last 15 years in numerous national, European and international space projects. Relevant examples are the European Hermes program, the German Sänger project, the European flight experiment ARD (Atmospheric Re-entry Demonstrator) or the development of the crew rescue vehicle of the international space station (X-38/CRV). The latter was investigated in the framework of a cooperation between the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). During this period major ground based test facilities, were designed and built at DLR. Important facilities with view to the design of spacecraft are the High Enthalpy Shock Tunnel Göttingen (HEG), the Trisonic Test Section Köln (TMK), the Hypersonic Wind Tunnel Köln (H2K) and the Arc Heated Facility Köln (L3K). The HEG is one of the major European ground based test facilities for the investigation of re-entry flows. In this free piston driven shock tunnel, hypersonic flows with total enthalpies up to 22 MJ/kg resulting in a free stream velocity of approximately 6 km/s can be generated. In such re-entry flows, classic aerodynamic problems are coupled with the influence of chemical reactions generated in the hot shock layer of a space vehicle by temperatures in excess of 10000 K. The operating conditions of HEG are designed in such a way that the oxygen and nitrogen dissociation relaxation behind the bow shock at model scale is equivalent to the full scale version at free flight conditions. The TMK and H2K are cold hypersonic wind tunnels. Their main purpose is to perform force, pressure and flow field measurements as basis for the design of high speed vehicles. The TMK allows to consider the Mach number range 0.5 to 5.7 with a special transonic test section and the H2K covers the range from M=5.3 to 11.2 applying different nozzles. The main purpose of the L3K is the characterization and qualification of thermal protection components of re-entry vehicles. Additionally, modern numerical tools were developed at DLR which allow the efficient computation of hot and cold hypersonic flows past complex configurations. Current and future activities are aimed at developing and further increasing the efficiency of numerical procedures, including the fluid-structure coupling, as well as the further improvement and development of facilities and measurement techniques in order to shorten analysis and development times and also to reduce design margins. The complexity of the design of space transportation vehicles and re-entry flows requires that experiments in ground based facilities are strongly linked with Computational Fluid Dynamics (CFD) investigations. These common activities range from the calibration process of the facility and the study of basic aerodynamic configurations, which are well suited to look at fundamental aspects of high enthalpy flow fields, to the investigation of realistic configurations. In the present paper some selected results obtained by the strong link between experiments and numerical rebuilding will be discussed.