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 CEAS Space Journal   [SJR: 0.221]   [H-I: 5]   [0 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1868-2510 - ISSN (Online) 1868-2502    Published by Springer-Verlag  [2355 journals]
• Design, integration and preliminary results of the IXV Catalysis
experiment
• Authors: Alan Viladegut; F. Panerai; O. Chazot; T. Pichon; P. Bertrand; C. Verdy; C. Coddet
Pages: 141 - 151
Abstract: The CATalytic Experiment (CATE) is an in-flight demonstration of catalysis effects at the surface of thermal protection materials. A high-catalytic coating was applied over the baseline ceramic material on the windward side of the intermediate experimental vehicle (IXV). The temperature jump due to different catalytic activities was detected during re-entry through measurements made with near-surface thermocouples on the windward side of the vehicle. The experiment aimed at contributing to the development and validation of gas/surface interaction models for re-entry applications. The present paper summarizes the design of CATE and its integration on the windward side of the IXV. Results of a qualification campaign at the Plasmatron facility of the von Karman Institute for Fluid Dynamics are presented. They provided an experimental evidence of the temperature jump at the low-to-high catalytic interface of the heat shield under aerothermal conditions relevant to the actual IXV flight. These tests also gave confidence so that the high-catalytic patch would not endanger the integrity of the vehicle and the safety of the mission. A preliminary assessment of flight data from the thermocouple measurements shows consistency with results of the qualification tests.
PubDate: 2017-06-01
DOI: 10.1007/s12567-016-0136-2
Issue No: Vol. 9, No. 2 (2017)

• Laser optics in space failure risk due to laser induced contamination
• Authors: D. Kokkinos; H. Schroeder; K. Fleury-Frenette; M. P. Georges; W. Riede; G. Tzeremes; P. Rochus
Pages: 153 - 162
Abstract: In this paper, a study of the evolution and morphology of UV laser-induced contamination (LIC) on optical surfaces due to hydrocarbons will be presented. LIC is a major hazard for lasers that operate in vacuum conditions. Recent studies have shown that the manufacturing method and cleaning of optical components can significantly mitigate LIC growth but never stop it completely. To better understand and model the evolution of LIC the deposition rate and transmission decay were observed via a CCD camera that measured laser induced fluorescence (LIF) and energy detectors, respectively. The affected sites were observed using Atomic Force Microscopy (AFM) and Phase Shift Interferometry (PSI). The LIC affected area diameters obtained by different experimental conditions were then compared with the theoretical prediction derived by the model. Very good agreement between this empirical model and the experimental results was found for the relevant parameter regimes under investigation. A novel methodology to determine the possibility of permanent optical damage due to LIC produced thermal effects is also discussed.
PubDate: 2017-06-01
DOI: 10.1007/s12567-016-0137-1
Issue No: Vol. 9, No. 2 (2017)

• Survey on the implementation and reliability of CubeSat electrical bus
interfaces
• Authors: Jasper Bouwmeester; Martin Langer; Eberhard Gill
Pages: 163 - 173
Abstract: This paper provides results and conclusions on a survey on the implementation and reliability aspects of CubeSat bus interfaces, with an emphasis on the data bus and power distribution. It provides recommendations for a future CubeSat bus standard. The survey is based on a literature study and a questionnaire representing 60 launched CubeSats and 44 to be launched CubeSats. It is found that the bus interfaces are not the main driver for mission failures. However, it is concluded that the Inter Integrated Circuit (I2C) data bus, as implemented in a great majority of the CubeSats, caused some catastrophic satellite failures and a vast amount of bus lockups. The power distribution may lead to catastrophic failures if the power lines are not protected against overcurrent. A connector and wiring standard widely implemented in CubeSats is based on the PC/104 standard. Most participants find the 104 pin connector of this standard too large. For a future CubeSat bus interface standard, it is recommended to implement a reliable data bus, a power distribution with overcurrent protection and a wiring harness with smaller connectors compared with PC/104.
PubDate: 2017-06-01
DOI: 10.1007/s12567-016-0138-0
Issue No: Vol. 9, No. 2 (2017)

• The TICTOP nozzle: a new nozzle contouring concept
• Authors: Manuel Frey; Konrad Makowka; Thomas Aichner
Pages: 175 - 181
Abstract: Currently, mainly two types of nozzle contouring methods are applied in space propulsion: the truncated ideal contour (TIC) and the thrust-optimized parabola (TOP). This article presents a new nozzle contouring method called TICTOP, combining elements of TIC and TOP design. The resulting nozzle is shock-free as the TIC and therefore does not induce restricted shock separation leading to excessive side-loads. Simultaneously, the TICTOP nozzle will allow higher nozzle wall exit pressures and hence give a better separation margin than is the case for a TIC. Hence, this new nozzle type combines the good properties of TIC and TOP nozzles and eliminates their drawbacks. It is especially suited for first stage application in launchers where flow separation and side-loads are design drivers.
PubDate: 2017-06-01
DOI: 10.1007/s12567-016-0139-z
Issue No: Vol. 9, No. 2 (2017)

• The TUBIN nanosatellite mission for wildfire detection in thermal infrared
• Authors: Merlin F. Barschke; Julian Bartholomäus; Karsten Gordon; Marc Lehmann; Klaus Brieß
Pages: 183 - 194
Abstract: The increasing number of wildfires has significant impact on the Earth’s climate system. Furthermore, they cause severe economic damage in many parts of the world. While different land and airborne wildfire detection and observation systems are in use in some areas of the world already, spaceborne systems offer great potential regarding global and continuous observation. TUBIN is a proof-of-concept mission to demonstrate the capabilities of a nanosatellite carrying lightweight infrared microbolometer arrays for spaceborne detection of wildfires and other high-temperature events. To this end, TUBIN carries two infrared microbolometers complemented by a CMOS imager. The TUBIN space segment is based on the TUBiX20 nanosatellite platform of Technische Universität Berlin and is the first mission that implements the full-scale attitude determination and control system of TUBiX20. Thereby, the TUBIN mission will demonstrate the platform’s ability to support a challenging Earth observation mission.
PubDate: 2017-06-01
DOI: 10.1007/s12567-016-0140-6
Issue No: Vol. 9, No. 2 (2017)

• Implementing model-based system engineering for the whole lifecycle of a
spacecraft
• Authors: P. M. Fischer; D. Lüdtke; C. Lange; F.-C. Roshani; F. Dannemann; A. Gerndt
Abstract: Design information of a spacecraft is collected over all phases in the lifecycle of a project. A lot of this information is exchanged between different engineering tasks and business processes. In some lifecycle phases, model-based system engineering (MBSE) has introduced system models and databases that help to organize such information and to keep it consistent for everyone. Nevertheless, none of the existing databases approached the whole lifecycle yet. Virtual Satellite is the MBSE database developed at DLR. It has been used for quite some time in Phase A studies and is currently extended for implementing it in the whole lifecycle of spacecraft projects. Since it is unforeseeable which future use cases such a database needs to support in all these different projects, the underlying data model has to provide tailoring and extension mechanisms to its conceptual data model (CDM). This paper explains the mechanisms as they are implemented in Virtual Satellite, which enables extending the CDM along the project without corrupting already stored information. As an upcoming major use case, Virtual Satellite will be implemented as MBSE tool in the S2TEP project. This project provides a new satellite bus for internal research and several different payload missions in the future. This paper explains how Virtual Satellite will be used to manage configuration control problems associated with such a multi-mission platform. It discusses how the S2TEP project starts using the software for collecting the first design information from concurrent engineering studies, then making use of the extension mechanisms of the CDM to introduce further information artefacts such as functional electrical architecture, thus linking more and more processes into an integrated MBSE approach.
PubDate: 2017-07-12
DOI: 10.1007/s12567-017-0166-4

• 3D thermography for improving temperature measurements in thermal vacuum
testing
• Authors: D. W. Robinson; R. Simpson; J. A. Parian; A. Cozzani; G. Casarosa; S. Sablerolle; H. Ertel
Abstract: The application of thermography to thermal vacuum (TV) testing of spacecrafts is becoming a vital additional tool in the mapping of structures during thermal cycles and thermal balance (TB) testing. Many of the customers at the European Space Agency (ESA) test centre, European Space Research and Technology Centre (ESTEC), The Netherlands, now make use of a thermal camera during TB-TV campaigns. This complements the use of embedded thermocouples on the structure, providing the prospect of monitoring temperatures at high resolution and high frequency. For simple flat structures with a well-defined emissivity, it is possible to determine the surface temperatures with reasonable confidence. However, for most real spacecraft and sub-systems, the complexity of the structure’s shape and its test environment creates inter-reflections from external structures. This and the additional complication of angular and spectral variations of the spacecraft surface emissivity make the interpretation of the radiation detected by a thermal camera more difficult in terms of determining a validated temperature with high confidence and well-defined uncertainty. One solution to this problem is: to map the geometry of the test specimen and thermal test environment; to model the surface temperatures and emissivity variations of the structures and materials; and to use this model to correct the apparent temperatures recorded by the thermal camera. This approach has been used by a team from NPL (National Physical Laboratory), Psi-tran, and PhotoCore, working with ESA, to develop a 3D thermography system to provide a means to validate thermal camera temperatures, based on a combination of thermal imaging photogrammetry and ray-tracing scene modeling. The system has been tested at ESTEC in ambient conditions with a dummy spacecraft structure containing a representative set of surface temperatures, shapes, and spacecraft materials, and with hot external sources and a high power lamp as a sun simulator. The results are presented here with estimated temperature measurement uncertainties and defined confidence levels according to the internationally accepted Guide to Uncertainty of Measurement as used in the IEC/ISO17025 test and measurement standard. This work is understood to represent the first application of well-understood thermal imaging theory, commercial photogrammetry software, and open-source ray-tracing software (adapted to realize the Planck function for thermal wavebands and target emission), and to produce from these elements a complete system for determining true surface temperatures for complex spacecraft-testing applications.
PubDate: 2017-07-11
DOI: 10.1007/s12567-017-0167-3

• Spacecraft formation control using analytical finite-duration approaches
• Authors: Mohamed Khalil Ben Larbi; Enrico Stoll
Abstract: This paper derives a control concept for formation flight (FF) applications assuming circular reference orbits. The paper focuses on a general impulsive control concept for FF which is then extended to the more realistic case of non-impulsive thrust maneuvers. The control concept uses a description of the FF in relative orbital elements (ROE) instead of the classical Cartesian description since the ROE provide a direct insight into key aspects of the relative motion and are particularly suitable for relative orbit control purposes and collision avoidance analysis. Although Gauss’ variational equations have been first derived to offer a mathematical tool for processing orbit perturbations, they are suitable for several different applications. If the perturbation acceleration is due to a control thrust, Gauss’ variational equations show the effect of such a control thrust on the Keplerian orbital elements. Integrating the Gauss’ variational equations offers a direct relation between velocity increments in the local vertical local horizontal frame and the subsequent change of Keplerian orbital elements. For proximity operations, these equations can be generalized from describing the motion of single spacecraft to the description of the relative motion of two spacecraft. This will be shown for impulsive and finite-duration maneuvers. Based on that, an analytical tool to estimate the error induced through impulsive maneuver planning is presented. The resulting control schemes are simple and effective and thus also suitable for on-board implementation. Simulations show that the proposed concept improves the timing of the thrust maneuver executions and thus reduces the residual error of the formation control.
PubDate: 2017-06-24
DOI: 10.1007/s12567-017-0162-8

• On the Radau pseudospectral method: theoretical and implementation
• Authors: Marco Sagliano; Stephan Theil; Michiel Bergsma; Vincenzo D’Onofrio; Lisa Whittle; Giulia Viavattene
Abstract: In the last decades the theoretical development of more and more refined direct methods, together with a new generation of CPUs, led to a significant improvement of numerical approaches for solving optimal-control problems. One of the most promising class of methods is based on pseudospectral optimal control. These methods do not only provide an efficient algorithm to solve optimal-control problems, but also define a theoretical framework for linking the discrete numerical solution to the analytical one in virtue of the covector mapping theorem. However, several aspects in their implementation can be refined. In this framework SPARTAN, the first European tool based on flipped-Radau pseudospectral method, has been developed. This paper illustrates the aspects implemented for SPARTAN, which can potentially be valid for any other transcription. The novelties included in this work consist specifically of a new hybridization of the Jacobian matrix computation made of four distinct parts. These contributions include a new analytical formulation for expressing Lagrange cost function for open final-time problems, and the use of dual-number theory for ensuring exact differentiation. Moreover, a self-scaling strategy for primal and dual variables, which combines the projected-Jacobian rows normalization and the covector mapping, is described. Three concrete examples show the validity of the novelties introduced, and the quality of the results obtained with the proposed methods.
PubDate: 2017-06-23
DOI: 10.1007/s12567-017-0165-5

• Repetitive laser ignition by optical breakdown of a LOX/H 2 rocket
combustion chamber with multi-injector head configuration
• Authors: Michael Börner; Chiara Manfletti; Gerhard Kroupa; Michael Oschwald
Abstract: This paper reports on the repetitive laser ignition by optical breakdown within an experimental rocket combustion chamber. Ignition was performed by focusing a laser pulse generated by a miniaturized diode-pumped Nd:YAG laser system. The system, which delivers 33.2 mJ in 2.3 ns, was mounted directly to the combustion chamber. The ignition process and flame stabilization was investigated using an optical probe system monitoring the flame attachment across the 15 coaxial injector configuration. 1195 successful ignitions were performed proving the reliability of this laser ignition system and its applicability to the propellant combination LOX/hydrogen at temperatures of $$T_{{{\text{H}}_{ 2} }}$$  = 120–282 K and $$T_{{{\text{O}}_{ 2} }}$$  = 110–281 K.
PubDate: 2017-06-19
DOI: 10.1007/s12567-017-0163-7

• Laser ignition of an experimental combustion chamber with a multi-injector
configuration at low pressure conditions
• Authors: Michael Börner; Chiara Manfletti; Gerhard Kroupa; Michael Oschwald
Abstract: In search of reliable and light-weight ignition systems for re-ignitable upper stage engines, a laser ignition system was adapted and tested on an experimental combustion chamber for propellant injection into low combustion chamber pressures at 50–80 mbar. The injector head pattern consisted of five coaxial injector elements. Both, laser-ablation-driven ignition and laser-plasma-driven ignition were tested for the propellant combination liquid oxygen and gaseous hydrogen. The 122 test runs demonstrated the reliability of the ignition system for different ignition configurations and negligible degradation due to testing. For the laser-plasma-driven scheme, minimum laser pulse energies needed for 100% ignition probability were found to decrease when increasing the distance of the ignition location from the injector faceplate with a minimum of 2.6 mJ. For laser-ablation-driven ignition, the minimum pulse energy was found to be independent of the ablation material tested and was about 1.7 mJ. The ignition process was characterized using both high-speed Schlieren and OH* emission diagnostics. Based on these findings and on the increased fiber-based pulse transport capabilities recently published, new ignition system configurations for space propulsion systems relying on fiber-based pulse delivery are formulated. If the laser ignition system delivers enough pulse energy, the laser-plasma-driven configuration represents the more versatile configuration. If the laser ignition pulse power is limited, the application of laser-ablation-driven ignition is an option to realize ignition, but implies restrictions concerning the location of ignition.
PubDate: 2017-06-19
DOI: 10.1007/s12567-017-0161-9

• All-fiber versatile laser frequency reference at 2 μm for CO 2
space-borne lidar applications
• Authors: Stéphane Schilt; Renaud Matthey; Kenny Hey Tow; Luc Thévenaz; Thomas Südmeyer
Abstract: We present a frequency stabilized laser at 2051 nm based on a versatile all-fibered stabilization setup. A modulation sideband locking technique is implemented to lock the laser at a controlled frequency detuning from the center of the CO2 R(30) transition envisaged for space-borne differential absorption lidar (DIAL) applications. This method relies on the use of a compact all-fibered gas reference cell that makes the setup robust and immune to mechanically induced optical misalignments. The gas cell is fabricated using a hollow-core photonic crystal fiber filled with pure CO2 at a low pressure of ~20 mbar and hermetically sealed at both ends by splices to silica fibers. Different configurations of this fibered cell have been developed and are presented. With this technique, frequency stabilities below 40 kHz at 1-s integration time and <100 kHz up to 1000-s averaging time were achieved for a laser detuning by around 1 GHz from the center of the CO2 transition. These stabilities are compliant with typical requirements for the reference seed source for a space CO2 DIAL.
PubDate: 2017-06-19
DOI: 10.1007/s12567-017-0164-6

• The PILOT optical alignment for its first flight
• Authors: B. Mot; Y. Longval; J.-Ph. Bernard; P. Ade; Y. André; J. Aumont; L. Bautista; N. Bray; P. deBernardis; O. Boulade; F. Bousquet; M. Bouzit; V. Buttice; A. Caillat; M. Chaigneau; C. Coudournac; B. Crane; F. Douchin; E. Doumayrou; J.-P. Dubois; C. Engel; P. Etcheto; P. Gélot; M. Griffin; G. Foenard; S. Grabarnik; P. Hargrave; A. Hughes; R. Laureijs; Y. Lepennec; B. Leriche; S. Maestre; B. Maffei; A. Mangilli; J. Martignac; C. Marty; W. Marty; S. Masi; F. Mirc; R. Misawa; J. Montel; L. Montier; J. Narbonne; J-M. Nicot; F. Pajot; G. Parot; E. Pérot; J. Pimentao; G. Pisano; N. Ponthieu; I. Ristorcelli; L. Rodriguez; G. Roudil; M. Saccoccio; M. Salatino; G. Savini; S. Stever; O. Simonella; P. Tapie; J. Tauber; C. Tibbs; J.-P. Torre; C. Tucker
Abstract: PILOT is a balloon-borne astronomy experiment designed to study the polarization of dust emission in the diffuse interstellar medium in our Galaxy at wavelengths 240 and 550 µm  with an angular resolution of about two arc-min. PILOT optics is composed of an off-axis Gregorian telescope and a refractive re-imager system. All these optical elements, except the primary mirror, are in a cryostat cooled to 3K. We used optical and 3D measurements combined with thermo-elastic modeling to perform the optical alignment. This paper describes the system analysis, the alignment procedure, and finally the performances obtained during the first flight in September 2015
PubDate: 2017-06-10
DOI: 10.1007/s12567-017-0159-3

• Using the attitude response of aerostable spacecraft to measure
thermospheric wind
• Authors: Josep Virgili-Llop; Peter C. E. Roberts; Zhou Hao
Abstract: In situ measurements of the thermospheric wind can be obtained by observing the attitude response of an aerostable spacecraft. In the proposed method, the aerostable spacecraft is left uncontrolled, freely reacting to the aerodynamic torques, and oscillating around its equilibrium attitude. The wind’s magnitude and direction is determined by combining the attitude observations with estimates of the other perturbing torques, atmospheric density, and spacecraft’s aerodynamic properties. The spatial resolution of the measurements is proportional to the natural frequency of the attitude’s oscillation. Spacecraft with high aerodynamic stiffness to inertia ratios operating at low altitudes exhibit higher natural frequencies, making them particularly suited for this method. A one degree-of-freedom case is used to present and illustrate the proposed method as well as to analyze its performance.
PubDate: 2017-06-09
DOI: 10.1007/s12567-017-0153-9

• Launch vehicle design and GNC sizing with ASTOS
• Authors: Francesco Cremaschi; Sebastian Winter; Valerio Rossi; Andreas Wiegand
Abstract: The European Space Agency (ESA) is currently involved in several activities related to launch vehicle designs (Future Launcher Preparatory Program, Ariane 6, VEGA evolutions, etc.). Within these activities, ESA has identified the importance of developing a simulation infrastructure capable of supporting the multi-disciplinary design and preliminary guidance navigation and control (GNC) design of different launch vehicle configurations. Astos Solutions has developed the multi-disciplinary optimization and launcher GNC simulation and sizing tool (LGSST) under ESA contract. The functionality is integrated in the Analysis, Simulation and Trajectory Optimization Software for space applications (ASTOS) and is intended to be used from the early design phases up to phase B1 activities. ASTOS shall enable the user to perform detailed vehicle design tasks and assessment of GNC systems, covering all aspects of rapid configuration and scenario management, sizing of stages, trajectory-dependent estimation of structural masses, rigid and flexible body dynamics, navigation, guidance and control, worst case analysis, launch safety analysis, performance analysis, and reporting.
PubDate: 2017-06-08
DOI: 10.1007/s12567-017-0160-x

• Development of micro-mirror slicer integral field unit for space-borne
solar spectrographs
• Authors: Yoshinori Suematsu; Kosuke Saito; Masatsugu Koyama; Yukiya Enokida; Yukinobu Okura; Tomoyasu Nakayasu; Takashi Sukegawa
Abstract: We present an innovative optical design for image slicer integral field unit (IFU) and a manufacturing method that overcomes optical limitations of metallic mirrors. Our IFU consists of a micro-mirror slicer of 45 arrayed, highly narrow, flat metallic mirrors and a pseudo-pupil-mirror array of off-axis conic aspheres forming three pseudo slits of re-arranged slicer images. A prototype IFU demonstrates that the final optical quality is sufficiently high for a visible light spectrograph. Each slicer micro-mirror is 1.58 mm long and 30 $$\upmu$$ m wide with surface roughness $$\le$$ 1 nm rms, and edge sharpness $$\le$$ 0.1 $$\upmu$$ m, etc. This IFU is small size and can be implemented in a multi-slit spectrograph without any moving mechanism and fore optics, in which one slit is real and the others are pseudo slits from the IFU. The IFU mirrors were deposited by a space-qualified, protected silver coating for high reflectivity in visible and near IR wavelength regions. These properties are well suitable for space-borne spectrograph such as the future Japanese solar space mission SOLAR-C. We present the optical design, performance of prototype IFU, and space qualification tests of the silver coating.
PubDate: 2017-06-07
DOI: 10.1007/s12567-017-0157-5

• Fused silica GRISMs manufactured by hydrophilic direct bonding at moderate
heating
• Authors: G. Kalkowski; K. Grabowski; G. Harnisch; T. Flügel-Paul; U. Zeitner; S. Risse
Abstract: For high-resolution spectroscopy in space, GRISM elements—obtained by patterning gratings onto a prism surface—find increasing applications. We report on GRISM manufacturing by joining the individual functional elements—prisms and gratings—to suitable components by the technology of hydrophilic direct bonding. Fused silica was used as a substrate material and binary gratings were fabricated by standard e-beam lithography and dry etching. Alignment of the grating dispersion direction to the prism angle was realized by passive adjustment on dedicated bonding gear matched to the substrate geometry. Materials adapted bonds of high transmission, stiffness, and strength were obtained after heat treatment at temperatures of about 200 °C in vacuum. Examples for bonding uncoated as well as coated grating surfaces are given. The results illustrate the great potential of hydrophilic glass direct bonding for manufacturing transmission optics to be used in space or other heavy duty applications.
PubDate: 2017-06-06
DOI: 10.1007/s12567-017-0158-4

• Cooperative rendezvous between two spacecraft under finite thrust
• Authors: Weiming Feng; Biao Wang; Kun Yang; Di Zhao
Abstract: Dynamic equations of orbital elements of a modified vernal equinox for a far-distance cooperative rendezvous between two spacecraft were set up in this paper. The process of the far-distance cooperative rendezvous was optimized by a hybrid algorithm combining particle swarm optimization and differential evolution. The convergent costate vectors were obtained and set as the initial values of sequential quadratic programming to search for precise solutions, and the results proved to be stable and convergent. It can be seen from the results that the flight time of the cooperative rendezvous would be largely saved the amplitude of the thrust would be increased if the other conditions are fixed, and the fuel consumption would not be increased. However, the flight time would no longer decrease when the amplitude of the thrust reaches a certain value. In the last section of this paper, cooperative rendezvous and active–passive rendezvous were compared and analyzed, showing the advantages of cooperative rendezvous when the initial conditions are the same.
PubDate: 2017-01-31
DOI: 10.1007/s12567-017-0145-9

• Analysis of the laser ignition of methane/oxygen mixtures in a sub-scale
rocket combustion chamber
• Authors: Michael Wohlhüter; Victor P. Zhukov; Joachim Sender; Stefan Schlechtriem
Abstract: The laser ignition of methane/oxygen mixtures in a sub-scale rocket combustion chamber has been investigated numerically and experimentally. The ignition test case used in the present paper was generated during the In-Space Propulsion project (ISP-1), a project focused on the operation of propulsion systems in space, the handling of long idle periods between operations, and multiple reignitions under space conditions. Regarding the definition of the numerical simulation and the suitable domain for the current model, 2D and 3D simulations have been performed. Analysis shows that the usage of a 2D geometry is not suitable for this type of simulation, as the reduction of the geometry to a 2D domain significantly changes the conditions at the time of ignition and subsequently the flame development. The comparison of the numerical and experimental results shows a strong discrepancy in the pressure evolution and the combustion chamber pressure peak following the laser spark. The detailed analysis of the optical Schlieren and OH data leads to the conclusion that the pressure measurement system was not able to capture the strong pressure increase and the peak value in the combustion chamber during ignition. Although the timing in flame development following the laser spark is not captured appropriately, the 3D simulations reproduce the general ignition phenomena observed in the optical measurement systems, such as pressure evolution and injector flow characteristics.
PubDate: 2016-12-27
DOI: 10.1007/s12567-016-0143-3

• Propulsive jet simulation with air and helium in launcher wake flows
• Authors: Sören Stephan; Rolf Radespiel
Abstract: The influence on the turbulent wake of a generic space launcher model due to the presence of an under-expanded jet is investigated experimentally. Wake flow phenomena represent a significant source of uncertainties in the design of a space launcher. Especially critical are dynamic loads on the structure. The wake flow is investigated at supersonic ( $$M=2.9$$ ) and hypersonic ( $$M=5.9$$ ) flow regimes. The jet flow is simulated using air and helium as working gas. Due to the lower molar mass of helium, higher jet velocities are realized, and therefore, velocity ratios similar to space launchers can be simulated. The degree of under-expansion of the jet is moderate for the supersonic case ( $$p_\mathrm{e}/p_\infty \approx 5$$ ) and high for the hypersonic case ( $$p_\mathrm{e}/p_\infty \approx 90$$ ). The flow topology is described by Schlieren visualization and mean-pressure measurements. Unsteady pressure measurements are performed to describe the dynamic wake flow. The influences of the under-expanded jet and different jet velocities are reported. On the base fluctuations at a Strouhal number, around $$\mathrm{St}_D \approx 0.25$$ dominate for supersonic free-stream flows. With air jet, a fluctuation-level increase on the base is observed for Strouhal numbers above $$\mathrm{St}_D \approx 0.75$$ in hypersonic flow regime. With helium jet, distinct peaks at higher frequencies are found. This is attributed to the interactions of wake flow and jet.
PubDate: 2016-12-24
DOI: 10.1007/s12567-016-0142-4

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