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

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

HEXAFLY-INT: An Overview of Waverider Subsonic Investigations

Hypersonic waveriders have the potential to significantly reduce travel times on long haul civilian transport routes. The design of hypersonic aircraft is heavily influenced by the aerodynamic efficiency at the cruise Mach number, resulting in less than ideal geometries for subsonic flight. Waverider aerodynamics and stability in the low speed regime is rarely investigated and not well understood, but is crucial for horizontal take-offs and landings. This paper gives an overview of all work completed within the HEXAFLY-INT project with respect to subsonic investigations. It covers a wide range of static and dynamic wind tunnel tests in the longitudinal and lateral-directional planes. The experimental investigations are complemented by in depth numerical computations which validate the experimental data. It was found that flow separation, non-linear vortex lift and subsequent bursting at high angles of attack govern the aircraft stability derivaties. This is due to the low aspect ratio, highly swept delta wings which are present on the vehicle, as well as sharp edges which give rise to high pressure gradients at moderate angles of attack

Subsonic Aerodynamics, Stability and Control of Hypersonic Waveriders

An overview of the techniques used to extract the flight mechanics derivatives required for a handling quality analysis as well as understand the mechanisms behind the behavior of the derivatives as they change with AoA/AoS or body axis rates for the Hexafly vehicl

A standard model for the investigation of aerodynamic and aerothermal loads on a re-usable launch vehicle

Aeronautical engineers have a long history of developing standardized models for wind tunnel calibrations and data comparisons between facilities. They are extremely useful in providing baseline datasets for correlation of results, data repeatability over time and verifying model installation or data acquisition systems. Reference models are also particularly relevant from the perspective of numerical analyses, where different assumptions and solver settings can be experimented with to determine solution sensitivity to certain parameters. A standardized reference model typically fulfills two main criteria. Firstly, they are simplistic in shape with a precisely defined geometry and secondly, they are representative of realistic configurations to ensure that the results are relevant. Examples of existing standard models include the AGARD-B, ONERA-M and the Standard Dynamics Model (SDM), which have been circulating for decades. Recently models such as the NASA CRM and the SSAM-Gen5 provide more up to date and relevant aircraft geometries from the past 10 to 20 years. While aeronautical engineers are well covered with standard aircraft models, the space community is not. Given the sudden and urgent interest in re-usable spacecraft over the past decade, a reference model which serves the research community in facilitating validation of numerical techniques in the generation of aerodynamic and aerothermal data over the entire trajectory is lacking. The purpose of this paper is to introduce a re-usable launch vehicle geometry where computational models and results will be made openly available to the research community. It is envisioned that this model will serve as a consistent validation case to promote collaboration and further research into the technical challenges associated with re-usable launch vehicles. This paper will first introduce the vehicle geometry and trajectory based on the flight path of in-service vehicles. Results from selected ascent and descent trajectory points will be presented and will contain aerodynamic coefficients and surface heating distributions. These are the first of many test cases which will look to address common questions with these types of vehicles, including but not limited to, surface heating through retro-propulsion and aerodynamic glide phases, plume-plume and plume-structure interactions, as well as vehicle stability and control

Low Speed Aerodynamics, Performance and Handling Qualities of a Hypersonic Waverider

Interest in the development of high speed commercial aircraft capable of travelling in excess of Mach 5 is on the increase. This is mainly driven by the potential of these vehicles to significantly reduce long haul flight times, connecting antipodal city pairs such as Brussels and Sydney in less than three hours. The hypersonic waverider concept has received particular attention because of its ability to achieve comparatively high aerodynamic efficiency at hypersonic cruise, as the body shock is contained by the wing leading edges. As research into the extreme conditions at high Mach numbers takes priority, no full subsonic handling quality analysis of a waverider has ever been completed, nor has an understanding of the mechanisms behind both static and dynamic stability been developed. This gap in literature is addressed by this thesis, which presents a combination of results from computational fluid dynamics simulations and wind tunnel experiments, completing the first full subsonic handling quality analysis of a waverider

Preparatory CFD Studies for Subsonic Analyses of a Reusable First Stage Launcher during Landing 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 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. Two successful campaigns analyzing the hypersonic re-entry burn phase of flight as well as the supersonic glide phase have been completed in the H2K and TMK facilities at DLR Cologne. The final phase of the RETPRO project looks to perform aerothermal tests by combusting H2/O2 during a retro burn in the subsonic VMK test section, simulating the landing environment. As was completed for the previous test campaigns, CFD reconstructions of selected tests are performed to evaluate the ability of RANS simulations to match the plume structure and flowfield, as well as surface pressure and heat flux measurements taken during the campaign. This paper will be primarily concerned with the CFD sensitivity studies conducted to determine the dependence of plume structure and surface measurements on factors such as grid density, combustion chamber conditions, wall temperature and turbulence model. Where possible, results from wind tunnel tests will be used to evaluate the combination of settings which best represent the experiments

Sustainable Space Technologies - Strategies towards a predictive Aerothermal Design of Re-Usable Space Transportation Systems

This paper presents a review of current aerothermal design and analysis methodologies for spacecraft. It briefly introduces the most important system architectures, including rockets, gliders, and capsule-based configurations, and gives an overview of the specific aerothermal and thermo-chemical effects that are encountered during their different flight phases and trajectories. Numerical and experimental design tools of different fidelity levels are reviewed and discussed, with a specific focus placed on the present limitations and uncertainty sources of models for the wide range of physical phenomena that are encountered in the analyses. This includes high temperature thermodynamics, chemical effects, turbulence, radiation, and gasdynamic effects. This is followed by a summary of current predictive capabilities and research foci, with missing capabilities identified. Finally, a future strategy toward an efficient and predictive aerothermal design of re-useable space transportation systems is proposed

Low speed lateral-directional aerodynamic and static stability analysis of a hypersonic waverider

status: publishe

Low speed longitudinal aerodynamic, static stability and performance analysis of a hypersonic waverider

status: publishe