Johan Steelant

Achievements Obtained for Sustained Hypersonic Flight within the LAPCAT-II Project

The design of hypersonic airbreathing vehicles is a challenging objective due to the intrinsic complexity of propulsion-airframe integration in combination with an engine cycle design able to operate over a wide Mach number range. This is one of the objectives of EC co-funded project LAPCAT-II aiming to reduce antipodal flights to less than 2 to 4 hours. Among the several studied vehicles in the preceding project LAPCAT-I, only aircraft designs for Mach 5 and 8 flights were retained in the present project. Starting from the available Mach 5 vehicle and its related pre-cooled turbo-ramjet, assumed performance figures of different components were now assessed in more detail numerically and experimental. Though the cruise flight of the Mach 8 vehicle based on a scramjet seemed feasible, further refinement was needed. In support to the integrated vehicle design, dedicated aerodynamic and propulsive experiments were done for the different components as well as for the complete vehicle. This included also the mutual verification of the windtunnels within Europe. In parallel, modelling implementation and validation on high-speed aerodynamics and propulsion were performed. The validated tools gave confidence to assess the performances of the fully integrated vehicles to comply with the mission goals. Finally, the impact of the emissions onto the climate was evaluated.

CFD Analysis of the HyShot II Scramjet Experiments in the HEG Shock Tunnel

Testing of the HyShot II scramjet configuration was carried out in the High Enthalpy Shock Tunnel Goettingen, HEG, of the German Aerospace Center, DLR. Computational fluid dynamics (CFD) is applied to support the analysis of experimental results and for the prediction of the free stream conditions in the HEG test section. Numerical simulations of the flow in the complete HyShot configuration for fuel on and off conditions were performed. This paper describes the laminar and turbulent modeling approaches for the CFD analysis and presents numerical results and their comparison to the experiment for both the HEG nozzle flow and the turbulent reacting flow in the HyShot Scramjet. The practicability of pressure-length scaling was tested by using further numerical analysis. Limits of applicability of this scaling approach were identified and are discussed in this paper

Ground Testing of the HyShot Supersonic Combustion Flight Experiment in HEG and Comparison with Flight Data

The first phase of the HyShot supersonic combustion ramjet (scramjet) flight experiment program of The University of Queensland in Australia was designed to provide benchmark data on supersonic combustion for a flight Mach number of approximately M=8. The second flight of the HyShot program, performed on July 30th 2002, was successful and supersonic combustion was observed along the specified trajectory range. The operating range of the High Enthalpy Shock Tunnel Gottingen (HEG) of the German Aerospace Centre (DLR) was recently extended. The facility now has the capability of testing a complete scramjet engine with internal combustion and external aerodynamics at M=7.8 flight con-ditions in altitudes of about 30 km. A post-flight analysis of the HyShot flight experiment was performed using an operational scramjet wind tunnel model with a geometry which is identical to that of the flight configuration.

Ground Testing of the HyShot II Scramjet Configuration in HEG

Ground based testing of the HyShot II supersonic combustion ramjet flight configuration was carried out in the High Enthalpy Shock Tunnel Gottingen, HEG, of the German Aerospace Center, DLR. The main focus of these investigations was to obtain surface pressure and surface heat transfer data on the intake and the cowl and body side surfaces of the combustion chamber and the nozzle. Further, high speed flow visualisation of the combustor flow was performed. Two HEG operating conditions which are related to 33km and 27km flight altitude were applied. Computational fluid dynamics (CFD) was applied to support the analysis of the experimental results and for the prediction of the free stream conditions in the HEG test section.

Experimental investigation of waterhammer in simplified feed lines of satellite propulsion systems

Operation of spacecraft propulsion systems is regularly adversely faced with waterhammer. The presence of very low pressures or vacuum complicate the classically known waterhammer due to various multiphase phenomena such as cavitation, absorption and desorption of a pressurizing gas, boiling, etc. This complex behavior is hard to model due to a lack of understanding of the physical processes taking place. To build up an experimental database on waterhammers in multiphase confined environments for validation of physical models, a literature survey was first undertaken on detailed waterhammer experiments. Only a few papers with well-documented experiments were found. None of the experiments found matched all the specifications needed for proper simulation and validation in satellite and spacecraft hardware and physical configurations. To complement the literature database, a detailed experimental investigation of the waterhammer phenomenon in a confined environment was required. This investigation was carried out using a simplified setup with two inert fluids, ethanol and acetaldehyde, and an actual propellant, monomethylhydrazine. Numerous tests were performed that confirmed excellent reproducibility of the results. The experiments showed that ethanol can be used instead of toxic monomethylhydrazine for estimating the waterhammer amplitude. The initial pipe pressure has a great influence on the waterhammer amplitude, but it would appear that the fluid vapor pressure is not a physical boundary with respect to waterhammer characteristics. The waterhammer phenomenon produced in a pipe with a low initial pressure exhibited a complex evolution over time and slight differences in amplitude and features according to the pipe geometry.

Conceptual Design of the High-Speed Propelled Experimental Flight Test Vehicle HEXAFLY

A concise overview of the overall layout of an experimental powered high-speed flight vehicle including its subsystems is given. A mission scenario, the different flight segments and events to which the payload is exposed are described and justified. This allowed the definition of the aero-thermo-mechanical loads required to conceptually design all elements on board of the vehicle. The final vehicle configuration could achieve the different mission objectives. In particular an aero-propulsive balance, i.e. thrust ≥ drag and lift ≥ weight, could be established at a cruise Mach number of M = 7.4 on the basis of a hydrogen powered scramjet engine while guaranteeing a good aerodynamic efficiency L/D ≥ 4 in a stable, trimmed and controlled way. The experimental combustion campaign could last for at least for 3s up to 9s pending on the finally obtained flight level. This test time is very valuable as it is about 3 orders of magnitude higher of what can be tested in European ground facilities. The vehicle made maximum use of databases, expertise, technologies and materials elaborated in previously EC co-funded projects ATLLAS I & II and LAPCAT I & II. Based on this conceptual design, the consortium has arrived at a key point where they feel comfortable to go to the next step in establishing a detailed design of the vehicle and the preparation of the launch vehicle and flight campaign.

Ground testing of the HyShot supersonic combustion flight experiment in HEG

The first phase of the HyShot supersonic combustion ramjet (scramjet) flight exper- iment program of The University of Queensland in Australia was designed to provide benchmark data on supersonic combustion for a flight Mach number of approximately M=8. The second flight of the HyShot program, performed on July 30th 2002, was successful and supersonic com- bustion was observed along the specified trajectory range. The operating range of the High Enthalpy Shock Tunnel Gottingen (HEG) of the German Aerospace Centre (DLR) was recently extended. The facility has now the capability of testing a complete scramjet engine with internal combustion and external aerodynamics at M=7.8 flight conditions in altitudes of about 30 km. A post flight analysis of the HyShot flight experiment was performed using an operational scramjet wind tunnel model with a geometry which is identical to that of the flight configuration.

Comparison of Supersonic Combustion Tests with Shock Tunnels Flight and CFD

In 2002, the HyShot supersonic flight experiment was successfully launched and allowed to access experimental flight data for supersonic combustion. Ground based testing performed in the High Enthalpy Shock Tunnel (HEG) of the German Aerospace Center (DLR) allowed to reproduce the Mach 7.8 flight conditions. The present numerical work focuses on the computation of the experiments in HEG considering flows with and without combustion and fuel injection. Further, variations of the equivalence ratio and the resulting influence on the flow topology are studied.

Design of a double diaphragm shock tube for fluid disintegration studies

A double diaphragm shock tube facility for studying liquid-spray atomization and combustion-related phenomena at elevated pressures and temperatures is described. The present shock tube is specifically intended for the investigation of fundamental processes related to fluid disintegration and mixing under realistic engine conditions. Special features of the facility include a variable-area driver section to compensate for shock attenuation, a square test section to allow flow visualization in the postshock region, a skimmer to dispose part of the boundary layer, a heated, fast-response injector, a fully automated gas-filling system, and a new control system and electronics. Test times of the order of 2-5 ms are possible with reflected shock pressures up to 50 bar and temperatures of 2000 K. Details on the setup design, construction and operation are given. Particular emphasis is placed on the accuracy and reproducibility of the test conditions. To that aim, qualification tests have been performed to assess the shock tube performance in terms of effectiveness of the skimmer concept, the capability to compensate for boundary layer effects and the generation of uniform and reproducible test and injection conditions.

EFFECT OF A COMPRESSIBILITY CORRECTION ON DIFFERENT TURBULENCE MODELS

ABSTRACT The inclusion of a compressibility correction into a turbulence model is required for the calculation of high Mach flows in free shear or wall bounded layers, as is the case for e.g. rocket nozzles, launchers or reentry vehicles. The quantitative effect of Wilcoxs dilatational dissipation model for advanced turbulence models is investigated for the numerical simulation of high-speed turbulent boundary layers in combination with both the linear low-Reynolds turbulence model of Wilcox as the non-linear SST-model of Menter. Both turbulence models, with and without compressibility correction, are verified against experimental investigations where oblique shock waves at various incidence angle interact on a flat plate turbulent boundary layer at Mach=5. Special attention is given to the reproduction of skin friction and heat transfer at different levels of shock wave-boundary layer interaction.