1,368 Works

Ultra High Temperature Ceramics: Densification, Properties and Thermal Stability

J.F. Justin & A. Jankowiak
Hypersonic flights, re-entry vehicles, and propulsion applications all require new materials that can perform in oxidizing or corrosive atmospheres at temperatures in excess of 2000°C and sometimes over the course of a long working life. Ultra High Temperature Ceramics (UHTCs) are good candidates to fulfill these requirements. Within this family, the ZrB2 and HfB2 based composites are the most attractive. The oxidation resistance of diboride-based compounds is better than that of SiC-based ceramics thanks to...

High Temperature Materials: an Introduction to Onera’s Contribution

Tasadduq Khan
The third issue of Aerospace Lab is dedicated to high temperature materials. Onera has been at the forefront of research and development for this class of materials for the past five decades, especially for aerospace engine applications. Starting in the mid 1960’s, many new materials and processes were invented, and cutting-edge research was carried out during this period. Similarly and concurrently, great progress has been made in mechanical modeling and lifing analysis, but a description...

Processing and Characterization of TiAl-based Alloys: Towards an Industrial Scale

M. Thomas & M.-P. Bacos
This paper highlights Onera efforts focused on the design of new TiAl-based alloys, the development of a commercially-viable route for the manufacture of aero engine components and the optimization of mechanical properties. The alloy G4, with a duplex microstructure, has been developed with an excellent balance of properties for gas turbine applications up to 800°C. Additionally, a series of TiAl-3(Fe,Zr,Mo) alloys have been designed for applications with good ductility requirements. Since these alloys were developed...

Potential of Directionally Solidified Eutectic Ceramics for High Temperature Applications

M. Parlier, R. Valle, S. Lartigue-Korinek & L. Mazerolles
Directionally solidified eutectic (DSE) ceramics add new potentialities to the advantages of sintered ceramics: a higher strength, almost constant, up to temperatures close to the melting point and a better creep resistance. The microstructure of melt-growth composites (MGC) of ceramic oxides consists in three-dimensional and continuous interconnected networks of single-crystal eutectic phases. After solidification of binary eutectics, the eutectic phases are alumina and either a perovskite or garnet phase. In ternary systems, cubic zirconia is...

Optical Diagnostics of Flows

Emmanuel Rosencher, Laurent Jacquin, Y. Le Sant, B. Aupoix, P. Barricau, M-C. Mérienne, G. Pailhas, P. Reulet, Y. Touvet, C. Brossard, J.-C. Monnier, F.-X. Vandernoot, F. Champagnat, G. Le Besnerais, A. Plyer, R. Fezzani, B. Leclaire, V. Bodoc, C. Laurent, Y. Biscos, G. Lavergne, N. Cézard, C. Besson, A. Dolfi-Bouteyre, L. Lombard … & F. Dupoirieux
Flow dynamics research is involved in all branches of science and technology: civil and chemical engineering, the automotive industry, energy, etc. Flow dynamics are even more central to aeronautics technology because they provide air lift to planes (non-reacting flow dynamics) as well as the moving impetus through combustion (reacting flow dynamics). The great challenges of flow dynamics require the validation of physical models with relevant lengths ranges spanning a dozen of orders of magnitude, from...

Principles and Applications of Particle Image Velocimetry

C. Brossard, J.-C. Monnier, P. Barricau, F.-X. Vandernoot, Y. Le Sant, F. Champagnat & G. Le Besnerais
In this paper, the principles of two-component Particle Image Velocimetry (PIV) and stereoscopic PIV are first recalled. Recent improvements in the camera calibration procedure for stereoscopic PIV are highlighted. The advantages of the PIV technique are illustrated through different studies performed in Onera laboratories for non-reacting or reacting flows, and various issues raised by the nature of fluid, flow dynamics, spatial and temporal resolutions, as well as data utilization, are examined. Finally, recent advances in...

Laser Absorption Spectroscopy to Probe Chemically Reacting Flows

A.K. Mohamed & M. Lefebvre
Laser absorption spectroscopy is now a well established tool to perform temperature, density and velocity measurements in a wide variety of aerodynamic and combustion flows. Measurements are usually performed on heterogeneous molecules like NO, CO, CO2 and H2O which present strong absorption line strengths in the infrared region due to their high dipole moments. In this paper, we present examples of applications using mid-infrared laser diodes in several hypersonic wind tunnels and combustion facilities of...

Influence of the plate leading-edge shape and thickness on the boundary layer laminar-turbulent transition at Mach number M=5

Sergey V. ALEKSANDROV, Eugenia A. ALEKSANDROVA, Volf Ya. BOROVOY, Vladimir E. MOSHAROV, Vladimir N. RADCHENKO & Alexander V. FEDOROV
The results of experimental study of boundary layer laminar-turbulent transition on a blunted plate with leading edges of various shapes and thicknesses at free-stream Mach number M=5 and unit Reynolds numbers Re1 from 1.5x107 to 9x107 m-1 are presented. The Reynolds number Reb, calculated by leading edge thickness b, was varied from 0 to 2x106. The following leading edge shapes were studied: cylinder, flat face, ellipse, and \"smoothed cylinder\". They were chosen by the results...

Analysis of the MOAO error budget obtained by CANARY at the WHT

F. Vidal, E. Gendron, G. Rousset, T. Morris, M. Brangier, A. Basden, Z. Hubert, R. Myers, F. Chemla, A. Longmore, T. Butterley, N. Dipper, C. Dunlop, D. Geng, D. Gratadour, D. Henry, P. Laporte, N. Looker, D. Perret, A. Sevin, G. Talbot & E. Younger
CANARY is the multi-object adaptive optics (MOAO) pathfinder for the multi object IR spectrometer EAGLE proposed on the European Extremely Large Telescope (E-ELT). CANARY was installed in September 2010 on the William Herschel Telescope (WHT) Canary Islands, Spain. For the first time, MOAO correction has been demonstrated using 3 widely separated off-axis natural guide stars and one deformable mirror in open loop in a target direction. We present the detailed analysis of the fourth night...

High-order AO in the visible: The Durham High-Order Demonstrator

Richard Myers, Alastair Basden, Nazim Bharmal, Nigel Dipper & Tim Morris
The Durham High-order Demonstrator (DHD) is a proposed high-order/extreme adaptive optics instrument design for the 4.2m William Herschel Telescope on La Palma, Canary Islands. Our principal interest in this instrument is designing a flexible-testbed for which we can develop a high-order AO system which is suitable for diffraction-limited, visible-light imaging. Additionally, it then becomes a facility which provides a high-order AO corrected beam for further instrument development such as coronography and thus XAO applications. This...

Direct imaging of habitable planets with ELTs

Olivier Guyon
The unprecedented angular resolution soon to be offered by extremely large telescopes (ELTs), together with recently developed high contrast imaging techniques (coronagraphy and wavefront control), can enable direct imaging and spectroscopic characterization of potentially habitable planets around nearby M-type stars. While the habitable zone of M stars is challenging to resolve, the planet to star contrast and the apparent brightness of the planet are highly favorable, thus providing the only opportunity for direct imaging and...

Mission Analysis and Preliminary Re-entry Trajectory Design of the DLR Reusability Flight Experiment ReFEx

Driven by the recently increased demand for investigating reusable launchers, the German Aerospace Center (DLR) is currently developing the Reusability Flight Experiment (ReFEx). The goal is to demonstrate the capability of performing an atmospheric re-entry, representative of a possible future winged reusable stage, and to develop and test key technologies for such reusable stages. The flight demonstrator ReFEx shall perform a controlled and autonomous re-entry from hypersonic velocity of approximately Mach 5 down to subsonic...

Laser Tomographic AO system for an Integral Field Spectrograph on the E-ELT : ATLAS project

T. Fusco, S. Meimon, Y. Clenet, M. Cohen, H. Schnetler, J. Paufique, V. Michau, N. Thatte, N. Hubin, C. Petit, P. Ammans, D. Gratadour, J.-M. Conan & P. Jagourel
ATLAS is a generic Laser Tomographic AO (LTAO) system for the E-ELT. Based on modular, relatively simple, and yet innovative concepts, it aims at providing diffraction limited images in the near infra-red for a close to 100 percent sky coverage.

Self-induced separation of the laminar boundary layer in a transonic flow.

To describe the self-induced separation of the laminar boundary, earlier mathematical models were created based on the use of asymptotic methods for the description of supersonic and subsonic regimes [1-2]. At the same time, the description of transonic modes remained unexplored, despite a number of papers in which individual regimes were considered.

Pathfinders to Extremely Large Telescope Adaptive Optics at W.M. Keck Observatory

Peter Wizinowich
The Keck II LGS AO system is extremely productive scientifically. The lessons learned from this AO system, and the AO development activities currently underway and planned for the Keck telescopes, offer excellent opportunities for pathfinders to ELT AO.

The LBT AO system on-sky results

S. Esposito, A. Riccardi, E. Pinna, A. Puglisi, F. Quiros-Pacheco, C. Arcidiacono, M. Xompero, R. Briguglio, G. Agapito, L. Busoni, L. Fini, J. Argomedo, P. Stefanini, P. Salinari, G. Brusa & D. Miller
The first LBT natural Guide Star Adaptive Optics system (FLAO#1) has been commissioned between May 2010 and June 2011. The system uses two key components namely the adaptive secondary mirror with 672 actuators and the pyramid sensor with up to 30x30 subapertures. During the on-sky commissioning the system reached very high performance for an 8m class telescope. Briefly, FWHM of 40mas and Strehl ratio higher than 90% have been measured in H band images together...

Towards MOAO on the ELT: the CANARY program

E. Gendron, T. Morris, F. Vidal, A. Basden, M. Brangier, Z. Hubert, R. Myers, G. Rousset, F. Chemla, A. Longmore, T. Butterley, N. Dipper, C. Dunlop, D. Geng, D. Gratadour, D. Henry, P. Laporte, N. Looker, D. Perret, A. Sevin, G. Talbot & E. Younger
From the very early concept presented in 2001 to the rst on-sky Multi-Object Adaptive Optics (MOAO) prototype system, exactly 10 years have elapsed. End of 2010, the pathnder instrument called CANARY obtained the rst open-loop, tomographically MOAO compensated images on the WHT. What were the challenges and what was demonstrated? What will be the future steps for a real astronomical MOAO system to be installed on an extremely large telescope (ELT)? We present the Canary...


Pinliang ZHANG, Zizheng GONG, Dongbo TIAN, Guangming SONG, Qiang WU, Yan CAO & Ming LI
An improved Meteoroids and Orbital Debris shielding structure for spacecraft is presented, using a bumper constructed from impedance-graded materials. The shielding performance of a shield enhanced by Ti-Al-nylon impedance-graded materials are investigated experimentally, using a two-stage light gas gun at velocities of 3.50 and 6.50 km/s, the critical diameter and ballistic limit curve are obtained. The results show that the shielding capability of a Ti-Al-nylon shield is greater than that of an aluminum Whipple shield...

Laboratory results for speckle suppression with a self-coherent camera.

Pierre Baudoz, Marion Mas, Raphael Galicher, Gerard Rousset & Johan Mazoyer
Direct imaging is a powerful tool for exoplanet atmosphere characterization. High performance of these techniques requires extreme wavefront correction for ground-based instruments as well as space projects. Wavefront sensors are usually physically separated from the common optics by a beam splitter in classical AO system. This separation introduces differential aberrations that are not measured by the wavefront sensor, which limits the performance of a planet finder instrument. We propose to use the Self-Coherent Camera (SCC)...

Pyramids, layers and no LGSs!

Roberto Ragazzoni, Marco Dima, Jacopo Farinato, Demetrio Magrin & Valentina Viotto
A decade after the first achievement into the improved capabilities in sensing by the pyramid wavefront sensor and from the outlining of novel classes of Multi Conjugated Adaptive Optics experimental verification of such approaches has been vastly proved by results from MAD onboard VLT and from FLAO onboard LBT. Refinement and extensions of these techniques promises to achieve similar goals within references scattered in a Field of View much larger than the one being compensated,...

Development of new analytical models for pressure and heat flux distributions on space debris afterbodies

In order to better predict the risk induced by orbital debris during their atmospheric re-entry, phenomena in the \"shadow region\" of the debris, i.e. the region that is not directly impinged upon by the freestream flow, were investigated. Four types of flow were shown to cause significant values of heat flux in the shadow region, for continuous hypersonic hyperenthalpic incoming flow conditions : attached flow, detached flow with fluid or solid reattachment, and shock-shock interactions....

Pyramid based locally closed loop wavefront sensor: an optomechanical study

D. Magrin, R. Ragazzoni, M. Bergomi, A. Brunelli, M. Dima, J. Farinato & V. Viotto
Pyramid wavefront sensors have shown their ability to achieve ultimate performances in terms of usage of starlight photons. Several of these advantages, however, do relay on the fact that the starlight is focused onto the pyramid pin after being properly corrected. While conventional adaptive optics systems (including multi conjugated ones) automatically imply such a feature this is not true for Multi Objects or non conventional Multi Conjugated AO systems, or more in general for the...

Identification of system misregistrations during AO-corrected observations

C. Bechet, J. Kolb, P.-Y. Madec, M. Tallon & E. Thiebaut
The adaptive optics facility (AOF) designed for the Very Large Telescope (VLT) in Chile will be equipped with a deformable secondary mirror (DSM). The calibration procedure of the interaction matrix, which characterizes the system and the relationship between the DSM commands and the wavefront sensors (WFS) slopes, will be more complex than for the previous systems at the VLT since it will have to be measured on sky and for a much larger number of...

The Slope-Oriented Hadamard scheme for in-lab or on-sky interaction matrix calibration

Serge Meimon, Cyril Petit & Thierry Fusco
The correct calibration of the interaction matrix affects the performance of an adaptive optics system. In the case of high-order systems, when the number of mirror modes is worth a few thousands, the calibration strategy is critical to reach the maximum interaction matrix quality in the minimum time. This is all the more true for the E-ELT, for which on sky calibration procedures have to be considered. Here, we first build a tractable interaction matrix...

AO Real-time Control Systems for the ELT Era

N.A. Dipper, A. Basden, D. Geng, E.J. Younger & R.M. Myers
Adaptive Optics systems for instruments on the next generation of astronomical telescopes will be of a significantly higher order than those for existing systems. The requirements for processing power for real-time computers to control such systems will be substantial and may well not be met by the simple application of the next generation of CPU based computers. We present here an overview of the various designs for future real-time computer systems that are being investigated...

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