CHANCE: A FRENCH-GERMAN HELICOPTER CFD-PROJECT

The paper gives an overview of the CHANCE research project (partly supported by the French DPAC and DGA and the German BMWA) which was started in 1998 between the German and French Aerospace Research Centres DLR and ONERA, the University of Stuttgart and the two National Helicopter Manufacturers, Eurocopter and Eurocopter Deutschland. The objective of the project was to develop and validate CFD tools for computing the aerodynamics of the complete helicopter, accounting for the blade elasticity by coupling with blade dynamics. The validation activity of the flow solvers was achieved through intermediate stages of increasing geometry and flow modelling complexity, starting from an isolated rotor in hover, and concluding with the time-accurate simulation of a complete helicopter configuration in forward-flight. All along the research program the updated versions of the CFD codes were systematically delivered to Industry. This approach was chosen to speed up the transfer of capabilities to industry and check early enough that the products meet the expectations for applicability in the industrial environment of Eurocopter

3D thermomechanical simulation of the secondary cooling zone of steel continuous casting

International audienceThis paper addresses the simulation of steel continuous casting (CC) using two non steady-state approaches: a slice method and a global method. Both methods can take into account the curvature of the CC machine. We describe the implementation of the two methods. We present the resolution of the thermo mechanical problem of the process. The two methods are compared in the case of CC of thick products

Analyse Numérique de l'effet du RPM sur le décochage dynamique observé sur un rotor d'hélicoptère lors d'un vol d'avancement à forte charge

International audienceDynamic stall is a highly complex phenomenon characterized by unsteady massive separated flow. It limits the flight envelope of helicopters by generating vibrations and large dynamic loads which can lead to fatigue and structural failure of blades. Dynamic stall involves several mechanisms which make the numerical prediction of stall difficult and the understanding of the phenomenon still incomplete. A loose coupling methodology between a Computational Fluid Dynamics and a Comprehensive Analysis codes is used to simulate the problem. Three stalled flight conditions have been selected in the wind tunnel 7A rotor test data to investigate the RPM effect on the dynamic stall onset and the related mechanisms. The lower the RPM, the more severe the stall is. A double stall has been observed on the lowest RPM case. The coupled simulations are in satisfactory agreement with experiment and are used to identify the mechanisms leading to stall. Simulations indicate that the blade-vortex interaction is an important factor in triggering the different stall events in these configurations.Le décrochage dynamique est un phénomène complexe caractérisé par d'importants décollements de la couche limite. Il constitue une limite du domaine de vol des hélicoptères puisqu'il génère des vibrations ainsi que de fortes variations de charge sur les pales ce qui peut mener à la fatigue puis à la rupture de celles-ci. La prédiction du décrochage dynamique à l'aide d'outils de simulation est toujours difficile puisque de nombreux phénomènes complexes sont impliqués ainsi la compréhension du décrochage dynamique reste encore incomplète. Dans cette étude, des simulations de couplage faible entre le code de CFD elsA et le code de structure HOST sont réalisées sur trois configurations de vol issues d'essais en souffleries à Modane. L'objectif étant d'évaluer l'influence du RPM sur l'apparition du décrochage. Il est montré que plus le RPM est faible, plus le décrochage est intense. En effet, deux événements de décrochage successifs sont observés dans le cas avec le plus faible RPM. Les simulations sont en très bon accord avec les résultats expérimentaux et peuvent donc être exploités pour une analyse des mécanismes du décrochage. Il est montré également que l’interaction pale – tourbillons semble être un facteur important dans le déclenchement du décrochage

Finite element thermomechanical simulation of steel continuous casting

International audienceIn continuous casting (CC), thermomechanical simulation is essential to analyze important issues: gap formation; stress and deformation of the solidified shell; bulging of product between supporting rolls in the case of steel CC; size of final product, butt-curl defect in direct chill casting of aluminium. The numerical simulation package THERCAST has been developed with the objective of supplying an accurate analysis of those phenomena, permitting to define relevant process actuators. In this paper, some characteristic features especially developed for steel continuous casting are presented and illustrated by examples of industrial application

Tool-life and wear mechanisms of CBN tools in machining of Inconel 718

The demand for increasing productivity when machining heat resistant alloys has resulted in the use of new tool materials such as cubic boron nitride (CBN) or ceramics. However, CBN tools are mostly used by the automotive industry in hard turning, and the wear of those tools is not sufficiently known in aerospace materials. In addition, the grade of these tools is not optimized for superalloys due to these being a small part of the market, although expanding (at 20% a year). So this investigation has been conducted to show which grade is optimal and what the wear mechanisms are during finishing operations of Inconel 718. It is shown that a low CBN content with a ceramic binder and small grains gives the best results. The wear mechanisms on the rake and flank faces were investigated. Through SEM observations and chemical analysis of the tested inserts, it is shown that the dominant wear mechanisms are adhesion and diffusion due to chemical affinity between elements from workpiece and insert

Réactivité de l'azote atomique et du radical OH à basse température par la technique CRESU (réactions d'intérêt pour l'astrochimie)

Plus d'une centaine de réactions entre des molécules stables et des radicaux se sont révélées être rapides à très basse température. Les réactions entre deux espèces radicalaires ont quant à elles reçu beaucoup moins d'attention de la part des scientifiques. Les complexités de production et de mesure de concentrations de ces radicaux en sont les principales raisons. Nous avons réalisé pour la première fois des mesures de constantes de vitesse sur les réactions radical-radical N + OH, N + CN et N + CH à basse température dans un réacteur à écoulement supersonique uniforme (tuyère de Laval). Nous avons utilisé une technique de décharge micro-onde pour produire l'azote atomique et une méthode de mesure relative pour déterminer les cinétiques des réactions. Les résultats donnent un aperçu des mécanismes de formation en phase gazeuse de l'azote moléculaire dans les nuages denses du milieu interstellaire.More than a hundred reactions between stable molecules and free radicals have been shown to remain rapid at low temperatures. In contrast, reactions between two unstable radicals have received much less attention due to the added complexity of producing and measuring excess radical concentrations. We performed kinetic experiments on the barrierless N + OH, N + CN and N + CH reactions in a supersonic flow (Laval nozzle) reactor. We used a microwave-discharge method to generate atomic nitrogen and a relative-rate method to follow the reaction kinetics. The measured rates agreed well with the results of exact and approximate quantum mechanical calculations. These results also provide insight into the gas-phase formation mechanisms of molecular nitrogen in interstellar clouds.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Stoichiometry and Grain Boundaries Control by Spark Plasma Sintering in Ba0.6Sr0.4TiO3:Mn/MgO Composites

LaNbO4/La3NbO7 and LaNbO4/LaNb3O9 cer-cer composites were prepared by impregnating Ca-doped LaNbO4 powder, synthesized by spray pyrolysis, with La- or Nb-precursor solutions. The sintering of the calcined powders was investigated by dilatometry, and dense composites were prepared by conventional sintering, hot pressing, and spark plasma sintering. The particle size of the starting powders was about 50 nm, and the average grain size of the dense materials ranged from 100 nm and upwards, depending on the sintering temperature, sintering procedure, and the phase composition. The unit cell parameters of LaNbO4 showed a finite size effect and approached the cell parameters of tetragonal LaNbO4 with decreasing crystallite size, both for the single-phase material and the composites. The minority phase (La3NbO7 or LaNb3O9) were observed as isolated grains and accumulated at triple points and not along the grain boundaries, pointing to a large dihedral angle between the phases. The calcium-solubility in the minority phases was larger than in LaNbO4, which corresponds well with previous reports. The electrical conductivity of the heterodoped materials was similar to, or lower than, that for Ca-doped LaNbO4

Investigation of unsteady flow development over a pitching airfoil by means of TR-PIV

The flow over an OA209 airfoil subjected to a sinusoidal pitching motion under dynamic stall conditions is investigated experimentally by means of time resolved particle image velocimetry (TR-PIV) and surface pressure measurements. Dynamic stall is distinguished by the formation and convection of large scale coherent structures and a delay in massive flow separation. A vortex detection scheme based on an identification function derived directly from the velocity fields is adopted to identify vortex cores. The combination of global time resolved imaging and an automated vortex identification algorithm allows for the investigation of the spatial and temporal evolution of vortical structures within a single oscillation. Furthermore, the mechanisms associated with the dynamic stall delay are considered

Experiencing a significant win and its sociodemographic and motivational predictors: A comparative analysis of pure-chance gamblers from Poland and France

Research on the relationship between wins and gambling behavior often focuses on winning considerably large amounts of money. It seems, however, that it is not the amount of the win, but the significance that the player assigns to the win, that exerts a decisive influence on gambling behavior. Therefore, in this study we adopted the concept of significant win: a win perceived by gamblers as important to them. The research aimed to discover what kind of wins are experienced as significant and what factors explain experiencing wins as significant. This study, conducted in Poland (N = 3,143) and France (N = 5,692), also had a comparative goal: discovering intercultural differences in experiencing significant wins. A computer-assisted web survey was administered to gamblers who engaged in pure-chance gambling, where the participant does not influence the outcome of the gamble after the initial bet is placed - selected from representative samples in both countries. We used logistic regression models to examine predictors of significant win experience in both countries and the differences between the countries. The results demonstrated that Polish gamblers more frequently considered a win significant when it was accompanied by strong, often negative emotions and was higher in monetary value normalized in terms of average monthly personal income, than French gamblers. French gamblers more frequently associated a significant win with a positive experience. The common predictors of a significant win experience in both countries were: being in debt, experiencing the win of a close person, gambling in a game of pure chance other than lotteries, more systematic pursuit of gambling, self-enhancement motivation, and coping motivation to gamble. Age at initiation into gambling was a significant predictor only in the French sample, whereas a financial motivation was a significant predictor in the Polish one. The results confirmed that the subjective perception of gambling wins is only partially related to the amounts of wins, which has practical implications for planning prevention strategies

Kinetics and Dynamics of the S(^1D_2) + H_2 \to SH + H Reaction at Very Low Temperatures and Collision Energies

We report combined studies on the prototypical S(^1D_2) + H2 insertion reaction. Kinetics and crossed-beam experiments are performed in experimental conditions approaching the cold energy regime, yielding absolute rate coefficients down to 5.8 K and relative integral cross sections to collision energies as low as 0.68 meV. They are supported by quantum calculations on a potential energy surface treating long range interactions accurately. All results are consistent and the excitation function behavior is explained in terms of the cumulative contribution of various partial waves