International Conference on Methods of Aerophysical Research, ICMAR 2008 RESEARCH TRAINING GROUP GRK 1095/1: "AERO-THERMODYNAMIC DESIGN OF A SCRAMJET PROPULSION SYSTEM" U. Gaisbauer 1), B. Weigand 2) 1) Institute for Aerodynamics and Gasdynamics, Universität Stuttgart, Pfaffenwaldring 21, 70569 Stuttgart 2) Institute of Aerospace Thermodynamics, Universität Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart Overview In the near future vehicles for hypersonic flight as well as new two-stage reusable space transportation systems will be required. To be able to reach the hypersonic flight regime the use of air breathing propulsion systems with supersonic combustion is the main problem to be solved concerning the design and the overall vehicle conception of hypersonic aircrafts. In this context only the use of a scramjet- propulsion system meets all the aerodynamic and gas dynamic requirements and offers a real alternative towards the classical rocket driven systems. Moreover, it must always be kept in mind that scramjet-technologies are one of the key technologies for hypersonic flight. Accordingly, in Germany a working group was founded to concentrate the activities taking place at different universities and to continue the work done in the three so called “hypersonic” Special Research Centres (SFB) for more then 14 years. Consequently, the main scientific objective of all these projects networked within this new “Research Training Group GRK 1095/1” is the design and the development of a scramjet demonstrator engine using necessarily different experimental and numerical procedures and tools, provided by the involved scientists. This scramjet demonstrator engine includes all the highly integrated components like forebody, inlet, isolator, combustion chamber and nozzle, assigned to their specific use. Moreover, the GRK 1095/1 has also an educational goal. Here, young scientists shall be brought together working on a fascinating topic. By structuring the PhD program a strong reduction for the PhD education is anticipated. Thus, the PhDs shall be completed after 3 years. Several partly coupled problems on different scientific areas appear. On the fields of aero- and gasdynamics, e.g. the precompression of the airflow is of main interest. Moreover on the field of aero-thermodynamics the main research activities are focused on the supersonic combustion itself as one of the key-problems of the whole project. Also materials research is included particularly to make fibre composites applicable for the highly thermal stressed combustion chamber. Parallel, other projects are dealing with the analysis of the global system, enabling therefore the very complex integration of all single components of the scramjet demonstrator engine. The present paper will give an overview about the included projects, the investigation program and will also present some first results. One particularity of the Research Training Group GRK 1095/1 is the involvement of three German universities as well as the DLR. Thus, scientists of the Universität Stuttgart, the RWTH Aachen, the Technische Universität München and the DLR Cologne are working together on the scramjet design. Detailed information concerning the Research Training Group GRK 1095/1 can be found online: www.uni-stuttgart.de/itlr/graduierten/. © U. Gaisbauer , B. Weigand , 2008 1 Section I 1. Introduction Since many years, but especially within the last 15 years, international big efforts were undertaken to develop an air breathing propulsion system, based on scramjet technology, for the flight in the hypersonic velocity regime. To prove this technology, tests with so called scramjet demonstrators have to be carried out. Consequently different kinds of demonstrators are used or planned. Here, complete scramjet powered hypersonic flight vehicles were used with a two-stage propulsion system. The first stage, a conventional rocket is needed to reach the scramjet operational conditions. After stage-separation and igniting the scramjet, the vehicle will perform a self-powered aerodynamic flight. This concept has successfully been tested within the NASA Hyper-X program [1] and will be applied within the European LEA testing program [2] and the Japanese research activities at JAXA. Another idea is to use single scramjet demonstrators, like the Russian KHOLOD hypersonic flight lab [3], a combination of a rotationally symmetric scramjet and a rocket, whereas the rocket permanently produces thrust even during the operational time of the scramjet. A clear analysis of the functional principle of the scramjet is very difficult. Another type of flying test bed consists of a scramjet demonstrator placed as a payload on the top of a rocket. In that case the rocket boosts the scramjet demonstrator to the apogee of its trajectory. Under the influence of gravity the demonstrator restarts to gather speed until the operational conditions are reached to ignite supersonic combustion while falling back on Earth. This type of test method is successfully working within the Australian HyShot program [4] and moreover should be a kind of “integrating concept” for the Research Training Group GRK 1095/1. To complete the list of activities in scramjet demonstrator testing, also the French national military PROMETHEE program [5] must be added. The given overview of only some selected research activities on the field of scramjet demonstrator testing, realised with enormous scientific and financial effort, demonstrates the international top-ranking position of the scramjet technology as a propulsion system for hypersonic vehicles or new two-stage reusable space transportation system. In Germany in 2005 the Research Training Group GRK 1095/1 was established on the base of already existing scientific know-how in the fields of scramjet technology and in hypersonic vehicles design. For more than 14 years international well established basic results have been worked out in the three former Special Research Centres (SFB 253, 255 and 259) [6]. These results and the already existing national and international scientific network, especially between the participating universities and institutes, enable the new working group to make a contribution to the actual research activities on scramjet systems. Coming from the technical point of view a scramjet is a highly integrated system with very strong interactions between all the necessary elements. Therefore, it is not possible to develop the corresponding single components separately. As soon as the first isolated numerical simulations and wind tunnel test have been done it is indispensable to merge all components like forebody with inlet, isolator, combustion chamber and nozzle to a demonstrator engine for further development. This predetermined technical interaction between the different components is typically for the cooperation and the networking of the whole Research Training Group. 2. Research Training Group GRK 1095 2.1 Fundamental design concept For the scramjet demonstrator, a basically two-dimensional design concept is selected which consists of a long double-wedge shaped forebody, an inlet with two outer compression ramps and moderate deflection angles, a subsequent diffusor (isolator), a supersonic combustion 2 International Conference on Methods of Aerophysical Research, ICMAR 2008 chamber and a single expansion ramp nozzle (SERN). The geometrical shape and basic dimensions result from the long-term goal to mount the demonstrator on a sounding rocket that boosts the payload to a specified height. At the apogee, the demonstrator separates from the rocket. As the system falls down to earth it gathers speed until the necessary velocity and dynamic pressure are reached to ignite the scramjet. Depending on the trajectory, a couple of seconds of supersonic combustion under real flight conditions are achievable. The flight-experiment oriented design of the demonstrator is used in order to have a technically relevant and applied test case, although the Research Training Group takes by now no part in the realization of such a flight experiment. Hence, flight dynamic problems, like stability and trajectory control, are not addressed in the first term of the project. A first test case, a stationary flight at an altitude of 32 km and at a flight Mach number of 8, is considered. 2.2 Structure The main goal of the Research Training Group is the aero-thermodynamic design of a scramjet propulsion system which integrates all parts of such an engine, like forebody, inlet, isolator, combustor and nozzle, and where each part is optimized for the chosen engine design point. Furthermore, thermo-mechanical analyses in regard to high-temperature materials for the combustion chamber as well as numerical system analyses of the complete engine are conducted. Even though, the actual conduction of the sounding rocket flight experiment is not part of the Research Training Group, the described scramjet demonstrator functions as a common objective for all projects involved. By aiming for that objective, each project has developed individual goals which, however, strongly interact with other projects and therefore have been highly tuned to one another. In respect to the flow over the forebody, experimental and numerical analyses are conducted to yield the influence of a specific forebody geometry on the inflow condition of the inlet and, thus, on the overall engine mass flux. Depending on different geometries and flight conditions (Mach number, Reynolds number), the boundary layer conditions are analyzed to determine