Thino Eggers

The Shefex Flight Experiment - Pathfinder Experiment for a Sky Based Test Facility

On Thursday, October 27th, 2005 the SHarp Edge Flight EXperiment SHEFEX has been successfully launched at the Andoya Rocket Range in northern Norway. The project, being performed under responsibility of the German Aerospace Center (DLR) flew on top of a two-stage solid propellant sounding rocket. One purpose of the experiment is the investigation of possible new shapes for future launcher or re-entry vehicles applying a shape with facetted surfaces and sharp edges and to enable the time accurate investi-gation of the flow effects and their structural answer during the hypersonic flight from 90 km down to an altitude of 20 km. Additionally, the SHEFEX project is a starting point for a series of experiments which enable the acquisition of important knowledge in hypersonic free flight experimentation and which are an excellent test bed for new technological concepts. The present paper gives an overview about the philosophy and the layout of ex- periment and introduces preliminary outcomes of the post-flight analysis.

Shock Tunnel Testing of the Transpiration-Cooled Heat Shield Experiment AKTiV

The present paper presents shock tube testing of the transpiration cooling experiment AKTiV flown on the sub-orbital re-entry body SHEFEXII. The campaign comprises testing of a 1:3 subscale model at original Reynolds number, Mach number and velocity, so that the subscaling has to be compensated for by rising the gas density. This, in turn, results in increased heat flux to the surface compared to the original. The shock tube experiments are supported by fluid dynamics computations by code TAU. Moreover, for lay out and design of the transpiration-cooled thermal protection element, the semi-analytical tool HEATS is introduced, based on a transient heat balance at the surface. Heat flux to the structure is measured just up- and downstream of the cooled sample. The measurement shows that heat flux is reduced upon coolant exhaust. Comparison of these results with HEATS shows that the heat flux predicted with HEATS is in good concurrence with the measured heat flux values at various angles of attack. HEATS results enables prediction of the cooling efficiency, giving an average heat flux reduction to 11.11% upon transpiration cooling for a coolant gas flow of 0.39 g/s and a variety of angles of attack.

Application of the Re-theta Transition Model in High Speed Flows

The prediction of boundary layer transition in high-speed flows plays a crucial role in the design of hypersonic vehicles. The paper contains a detailed description of a correlation-based transition model using local variables, namely the Langtry-Menter transition model. The model was implemented into DLR-TAU code and tested for hypersonic test cases obtained by other partners. Discussions of the physical background as well as the fundamental understanding of the main variables, correlations and functions inside the model are provided. Test results show that direct applications of the model for high-speed flows can capture hypersonic transition. For the blunted double ramp case, the present model can accurately predict the transition process. However, for the shock impingement cases with assigned sharp leading edges, the present model tends to over-estimate the heat flux by over 30% than the experimental data. This suggests a further detailed study of both numerical and experimental settings.

Numerical Analysis of the SKYLON Spaceplane in Hypersonic Flow

The paper investigates selected hypersonic flow conditions along the SKYLON re-entry trajectory based on Navier-Stokes simulations with the DLR TAU code. The obtained surface values are compared in order to find the most critical flow condition with respect to the maximum heat flux and the surface temperatures.

Application of a Coupling of Aerodynamics and Flight Dynamics to the SHEFEX I Flight Experiment

Numerical predictions by coupling different aerodynamic codes with the trajectory optimization program REENT 6D are presented in this paper. For mission analysis, the trajectory program is coupled to missile DATCOM and altitude and roll rates are compared with flight data. For detailed analysis, the unsteady Euler equations including rigid body motion are solved using the DLR TAU code. Firstly, the roll behavior during the ascent phase of the vehicle is analyzed, and secondly some parts of the re-entry phase of the SHEFEX I flight experiment are compared with flight measurements. Assuming that the fins of the second stage are canted, the overall agreement with flight data is satisfactory.

Experimental and Numerical Analysis of SHEFEX-II

The SH arp E dge F light EX periment (SHEFEX) of the German Aerospace Center (DLR) has been established to demonstrate the feasibility of space vehicles with facetted Thermal Protection System (TPS). In this study, first results to the aerothermodynamic behavior of SHEFEX − II in the High Enthalpy Shock Tunnel Gottingen (HEG) are presented.The main focus is on the experimental and numerical investigation of the active cooling experiment AKTiV. The measured and calculated results confirm that a cooling effect is feasible.

Hypersonic boundary-layer stabilization by means of ultrasonically absorptive carbon-carbon material Part 2: Computational Analysis

The damping of acoustic second mode instabilities by passive porous surfaces is investigated numerically and compared with experiments for different hypersonic boundary-layer flows. The used geometry is a blunt 7° half-angle cone model with exchangeable nose. The cone surface consists partly of an ultrasonically absorptive material, which has a natural, random porosity. For the analyses of the second modes the DLR stability code NOLOT, NOnLocal Transition analysis code, is used. The influence of the nose radius and the unit Reynolds number on the second modes is investigated using a smooth surface. These results of the smooth surface are compared with those of the porous surface to study the damping effect on the second modes and the transition shift. The numerical results are compared with wind tunnel measurements, which were performed in the DLR High Enthalpy Shock Tunnel Gottingen (HEG).

Passive hypersonic boundary layer control by means of ultrasonically absorptive carbon-carbon ceramics: Investigations of different boundary conditions

The influence of carbon fiber reinforced carbon ceramic (C/C) surfaces on hypersonic boundary layer instabilities is analysed numerically using the stability code NOLOT, NOn-Local Transition analysis code, of the German Aerospace Center (DLR). Experimental investigations in the DLR High Enthalpy Shock Tunnel Gottingen, HEG, show that C/C surfaces can be utilized to damp acoustic second mode instabilities, which results in a delay of boundary layer transition onset. The investigated geometry is a blunt 7° half-angle cone model with a nose radius of 2.5 mm and a total length of about 1 m. One-third of the metallic model surface in circumferential direction was replaced by C/C ceramics. In this paper different approaches for the formulation of the boundary conditions in NOLOT, modeling the acoustic damping properties of the C/C material, are analysed and compared with the experimental results.

Comparison of Faceted and Blunt Lifting Bodies for Reentry Flights

The design of a reentry vehicle strongly depends on the entry strategy of the projected mission. From the aerodynamic point of view, the layout of a hypersonic vehicle is a compromise between a vehicle being blunt enough to reduce the aerodynamic heating and sharp enough to obtain acceptable aerodynamic and propulsive efficiency. The selected flight configurations in this paper are wingless lifting bodies. Two different types of lifting bodies are compared: a sharp and a blunt body. The chosen blunt bicone is one of the Reusability Flight Experiment geometries, which were designed in the frame of the DLR, German Aerospace Center vehicle concept study of Reusability Flight Experiment. The sharp configuration is one of the DLR, German Aerospace Center Sharp Edge Flight Experiment configurations, which are a faceted body with sharp leading edge. The focus of the present study is the discussion of advantages and drawbacks of both concepts with respect to structure and aerodynamics.

Passive hypersonic boundary layer control: The Potential of an Ultrasonically Absorptive Ceramic for HEXAFLY-INT

The potential of ceramic matrix composites (CMC) for passive boundary layer transition control on the hypersonic flight vehicle HEXAFLY-INT is investigated. CMC can be manufactured as ultrasonically absorptive ceramic: for the presented numerical investigations carbon fiber reinforced carbon material (C/C) is used for the passive damping of acoustic second mode instabilities. The analyses are performed with the stability code NOLOT, NOnLOcal Transition analysis, of the German Aerospace Center (DLR). The boundary conditions of the NOLOT code are extended for the application of random porous surfaces and consider the acoustic properties of the C/C. In this paper a trajectory segment of interest for the application of ultrasonically absorptive ceramics on the HEXAFLY-INT hypersonic glider is investigated. For chosen flight conditions and a corresponding test condition of the DLR High Enthalpy Shock Tunnel Gottingen (HEG) detailed stability analyses with NOLOT are performed: this includes the investigation of the second mode damping due to the passive porous ceramic.