Reconstruction of Wind Tunnel Tests using CFD for a Reusable First Stage during Rocket Retro-Propulsion

The RETPRO project (Validation of Wind Tunnel Test and CFD Techniques for Retropropulsion), as part of ESA's Future Launcher Preparatory Programme, aims at preparing the tools, necessary for a reliable design and simulation of future rocket launchers or spacecraft. A particular focus is assigned to vertical take-off and landing configurations using retro propulsion as part of their control concept for entry, descent, and landing manoeuvres. Wind tunnel tests and computational fluid dynamics are used to generate a comprehensive aerodynamic database, which is required for flight dynamics simulations, enabling mission and performance analyses of possible future launcher designs. This paper focuses on the presentation and discussion of steady-state numerical simulation results which reconstruct selected wind tunnel tests during both powered and unpowered descent phases. The CFD simulations cover a Mach number range from 2 up to 7, with dry air used to model the exhaust plume. Typical flow topologies and features are discussed, with quantitative results coming from a comparison of force balance and surface pressure measurements between experimental results and CFD simulations. Schlieren images from the experiments are used to evaluate the plume structure and shock stand-off distances. For the unpowered descent cases the agreement between schlieren images, force and pressure measurements is extremely strong. During powered descent the basic plume structure is captured well despite the highly unsteady and fluctuating flow field. Pressure and force measurements gave mixed results, but overall the studies show that RANS simulations perform well compared to experimental data

Hypersonic Retrograde Propulsion Experiments - A Basis for Validation of CFD within RETPRO

The paper focuses on wind tunnel tests of the hypersonic re-entry part of the RETPRO descent trajectory. The re-usable rocket launcher configuration is investigated including active retro-propulsion at Mach 5.3 and 7.0 in the Hypersonic Wind Tunnel (H2K) of DLR, Cologne. Results from high-speed Schlieren imaging, force and unsteady wall pressure measurements are output for CFD accuracy assessment and validation. Variations of the number of active engines, thrust coefficient, jet temperature and angle of attack are performed to gather detailed information on sensitivities of characteristic mean and dynamic flow features. It is shown that the dynamic behavior of the retro-propulsion flow field is significantly altered by the engine configuration. A stable quasi-steady mode with overlaying shock oscillation is found for the one engine case, while three engine operation leads to a turbulent flow field with random flipping between a short and a long jet penetration mode. The oscillation frequency and temporal characteristics of the retro-propulsion flow field are found to be sensitive to the thrust coefficient and jet reservoir temperature

Condensation Modelling of Expanding Cold Gas Jets during Hypersonic Retro-Propulsion Manoeuvres within the RETPRO Project

The RETPRO project (Validation of Wind Tunnel Test and CFD Techniques for Retropropulsion), as part of ESA’s Future Launchers Preparatory Programme, aims at preparing the tools, necessary for a reliable design and simulation of future rocket launchers or spacecraft. A particular focus is assigned to vertical take-off and landing configurations using retro propulsion as part of their control concept for entry, descent, and landing manoeuvres. Wind tunnel tests and computational fluid dynamics are used to generate a comprehensive aerodynamic database, which is required for flight dynamics simulations, enabling mission and performance analyses of possible future launcher designs. Windtunnel tests are conducted in the DLR Cologne H2K facility, with room temperature dry air ejected through selected nozzles to simulate the exhaust plume. Condensation effects might occur in the plume due to the low static freestream pressure at Mach 7, combined with the expanding flow in the nozzle. This paper presents results from numerical investigations including a vapour-equilibirum model which evaluate the potential influence of plume condensation on measured data in the wind tunnel. A qualitative comparison between experimental and numerical results is presented through Schlieren photographs. Condensation was observed in the numerical results, causing the flow path in and around the plume to be altered. Surface pressure coefficients in the condensation case were observed to be approximately 5% lower than when using the standard ideal gas model. Finally, the shock stand off distance was reduced, but not significantly. The comparison with tunnel data was therefore more-or-less the same as with the ideal gas model and the use of the condensation model was not deemed necessary for subsequent computations

Design of a Hot Plume Interaction Facility at DLR Cologne

Space transportation systems are exposed to high thermal and mechanical loads during the ascend in the transonic flow regime. By now, there are still many uncertainties, which can not be solved with state of the art computational fluid dynamic models or experiments with cold jet flows. A test facility with a high degree of similarity to flight with respect to the influence of the hot nozzle flow can contribute to improve the understanding of interaction effects between the hot nozzle flow and the ambient flow by providing reliable data for validation. The objective of the paper at hand is to present the work progress on such a facility. Issues and challenges concerning the base flows are discussed and potential research areas for investigations are considered. Relevant conditions during the ascend of Ariane 5 are used as baseline and appropriate scaling laws are discussed to conclude requirements for the operational conditions for the existing wind tunnel Vertical Test Section Cologne (VMK). These operational conditions are used to develop a concept. After a proof of concept is given by CFD calculations, details to the supply system including the operational range are described and opposed to existing test benches without interaction capabilities

Numerische Untersuchung eines plasmagetriebenen Jet-Aktuators zur aktiven Beeinflussung von Hochgeschwindigkeitsströmungen

Die Konfiguration, Durchführung und Validierung einer vollständigen numerischen Simulation eines plasmasynthetischen Jet-Aktuators anhand des freien Softwarepaketes OpenFoam wird präsentiert. Sie erfolgt unter der Zielsetzung, die Simulation als Werkzeug für den Auslegungsprozess von Aktuationssystemen und als Ausgangspunkt für zukünftige ressourceneffiziente Simulationen von Mehrfachanordnungen und Regelkreisen zu qualifizieren. Im Referenzfall wird ein vollständiger Zyklus, bestehend aus Ausstoß- und Regenerationsphase von 1000µs simuliert. Anschließend werden die Ergebnisse anhand verschiedener Vergleichssimulationen und Parametervariationen mithilfe von experimentellen und literaturgestützten Daten validiert

Entwicklung und Charakterisierung eines plasmagetriebenen Jet-Aktuators zur aktiven Beeinflussung von Hochgeschwindigkeitsströmungen

Gegenstand der vorliegenden Arbeit ist die Entwicklung, Realisierung und Charakterisierung eines plasmagetriebenen Jet-Aktuationssystems zur aktiven Beeinflussung von Hochgeschwindigkeitsströmungen mit Hilfe geeigneter, experimenteller Messmethoden. Die betriebscharakteristischen Eigenschaften des Aktuators, dessen Design sich dabei an dem bereits bekannten Prinzip des SparkJet-Aktuators orientiert, wurden hierzu in der Versuchsumgebung bei ruhenden Umgebungsbedingungen anhand einer Variation verschiedener thermischer und geometrischer Parameter mit Hilfe elektrischer Messtechnik und foto-, sowie schlierenoptischer Visualisierungsverfahren bestimmt

GH2/GO2 Supply Facility for Hot Plume Testing in the Vertical Test Section Cologne (VMK)

The paper belongs to a series of investigations of hot plume interaction phenomena in the field of space transportation. Scientific motivation of these investigations is the understanding of the physical mechanisms in base flows that are for example present at rocket launchers. The paper shortly summarizes the technical challenges that are resulting from base flow interaction phenomena and develops a motivation for an enhancement of the experimental testing capabilities in that field. In the second part, an effort of the German Aerospace Center (DLR) to achieve that goal by expanding the vertical wind tunnel facility in Cologne by a gaseous hydrogen oxygen supply unit to enable hot plume interaction testing with GH2/GO2 combustion is presented. The design of the facility is summarized and an outlook on the gain for future investigations in that field is given in the conclusions

Characterization of a GH2/GO2 Combustor for Hot Plume Wind Tunnel Testing

After entry into operations of the newly implemented GH2/GO2 supply facility for hot plume testing at the German Aerospace Center (DLR), Cologne, facility operation in combination with the preliminary GH2/GO2 rocket combustion chamber is being characterized in order to qualify the test environment for future wind tunnel tests. The combustion chamber will be implemented into a generic rocket model to generate a realistic hot exhaust jet for interaction experiments with the transonic ambient flow, provided by the Vertical Test Section Cologne (VMK). Two reference configurations, that will be subject to investigation within the wind tunnel campaign, are characterized in the present paper by the facility operating parameters, combustion chamber pressure, and wall temperature distribution. An evaluation of the pressure fluctuation amplitudes, together with spectral analyzes is used for a classification of the state of combustion. The result is a summary of the different test cases with a discussion of their qualification for wind tunnel testing and an outlook on possible measures to extend the operating range for an enhanced range of similarity parameters

Launch of the GH2/GO2 Supply Facility for Hot Plume Testing at DLR Cologne

The paper describes the actual state of the GH2/GO2 supply facility that has been established at the DLR site in Cologne to give a new perspective to the investigation of rocket afterbodies with hot plumes in experimental testing. In 2016, the basic concepts of the facility design were presented. These have now been fully realized and the facility has been put into operation by summer 2017. Its purpose will be to provide our Vertical Wind Tunnel test section (VMK) with combustible mixtures of gaseous hydrogen and oxygen for the operation of a model integrated rocket combustion chamber, to produce hot plumes with realistic stagnation properties and exit velocities. The model will be a generic rocket launcher that is subjected to ambient flow in the subsonic to transonic regimes. For the characterization of the operating range in terms of total pressure, temperature and mixing ratio, a stand-alone thrust chamber for static ambient condition has been developed and operated in the start-up. Setup, results, and the consequential outlook to future wind tunnel tests are presented in this article

Interaktionsteststand für realistische Raketentreibstrahlen mit umströmender Atmosphäre

Beim Deutschen Zentrum für Luft- und Raumfahrt (DLR) in Köln wurde ein einzigartiger Teststand zur Simu-lation der Strömungsinteraktion zwischen heißen Raketentreibstrahlen und der umströmenden Atmosphäre errichtet. Untersucht werden generische Raketenheckkonfigurationen im Modellmaßstab innerhalb der Verti-kalen Messstrecke Köln (VMK). Die heiße Komponente des Raketentreibstrahls wird mithilfe einer im Modell integrierten Wasserstoff-Sauerstoff-Brennkammer erzeugt, die mit den gasförmigen Verbrennungsedukten bis max. 115 bar versorgt werden kann. Hierdurch wird die Erzeugung von Treibstrahlen bei realistischen Düsendruckverhältnissen und gleichzeitig hohen Austrittsgeschwindigkeiten ermöglicht, welche erstmalig eine experimentelle Untersuchung der Interaktionsphänomene der Raketenheckströmung unter flugrelevanten Bedingungen zulässt. Die Untersuchungen werden primär dem Sonderforschungsbereich TRR40 zur Verfügung gestellt, wo sie im Teilbereich B durch weitere experimentelle und numerische Untersuchungen komplettiert werden. Es wird die dazu benötigte Infrastruktur nebst Ergebnissen der Inbetriebnahme sowie der bisherigen Anlagencharakterisierung vorgestellt