21549 research outputs found
Sort by
Méthodes numériques pour la simulation aux grandes échelles LES monocanal d'étages de turbomachines
Get PDFL'industrie aéronautique et en particulier celle qui s’intéresse aux turbomachines cherche en permanence à optimiser l’aérodynamique pour réduire la consommation de carburant ainsi que les émissions de polluants et notamment de gaz à effet de serre. Cette recherche passe par l’étude précise des différents modules pour vérifier un certain nombre d'éléments critiques tels que la marge au pompage, les niveaux de température pour la tenue des matériaux, les domaines d'opérabilité, etc. Les simulations instationnaires, dont les simulations aux grandes échelles (SGE) font partie, sont d'excellentes candidates pour pouvoir rendre compte de toute cette complexité, en particulier les interactions entre éléments et modules d'une turbine à gaz. Cependant, le coût de calcul pour un compresseur ou une turbine est tel que ce type de simulations n'est pas accessible pour le domaine industriel. Afin de réduire ces coûts, différents choix sont possibles. Du point de vue purement géométrique, les nombres d'aubage des étages de turbomachines étant la plupart du temps premiers entre eux, il est nécessaire de simuler l'intégralité azimutale de la machine pour prédire correctement les écoulements. Ainsi, cette thèse s’intéresse à l’étude de deux méthodes de réduction de taille de domaine pour les étages de turbomachines par des approches mono ou bi canal dans l’optique de rendre plus abordables les SGE. La méthode profile transformation (PTA) permet de transmettre l'information de part et d'autre de l'interface rotor stator à l'aide d'une mise à l'échelle géométrique. L'impact de l'hypothèse est évalué analytiquement, puis sur des cas de complexité croissante depuis un cas académique jusqu'à une turbine haute-pression industrielle. La méthode basée sur la périodicité spatio-temporelle de l'écoulement, appelée hypothèse chorochronique, est ensuite étudiée. Une condition limite particulière est conçue pour la gestion des bords azimutaux et une première évaluation est menée sur un cas académique de sillages défilants. Le même cas est utilisé pour valider la méthode complète constituée du traitement chorochronique aux bords azimutaux et à l'interface rotor stator. Dans une dernière partie, les deux méthodes sont comparées sur une configuration industrielle d'un étage de compresseur haute-pression
Bayesian optimization for mixed variables using an adaptive dimension reduction process: applications to aircraft design
No full textMultidisciplinary design optimization methods aim at adapting numerical optimization techniques to the design of engineering systems involving multiple disciplines. In this context, a large number of mixed continuous, integer and categorical variables might arise during the optimization process and practical applications involve a large number of design variables. Recently, there has been a growing interest in mixed variables constrained Bayesian optimization but most existing approaches severely increase the number of the hyperparameters related to the surrogate model. In this paper, we address this issue by constructing surrogate models using less hyperparameters. The reduction process is based on the partial least squares method. An adaptive procedure for choosing the number of hyperparameters is proposed. The performance of the proposed approach is confirmed on analytical tests as well as two real applications related to aircraft design. A significant improvement is obtained compared to genetic algorithms. https://arc.aiaa.org/doi/pdf/10.2514/6.2022-008
Modelling load transfer in single-lap adhesively bonded and hybrid (bolted / bonded) joints
Get PDFAn aerospace structure is built from the assembly of structural sub-components involving joining technologies such as welding, mechanical fastening or adhesive bonding.
The function of joints is to ensure load transfer between the structural sub-components. The integrity of the structure directly depends on strength of these joints. In order to design these critical structural areas, load transfer between structural sub-components must be assessed. The objective of this review paper is to present approaches for the simplified modelling and associated resolution schemes of single-lap adhesively bonded and hybrid (bolted/bonded) joints to predict load transfer. We show that the scope of available closed-form solutions is restricted, such that the use of semi-analytical schemes is suitable. Macro-element modelling is then presented. This technique allows the assessment of load transfer and associated stresses, especially in the adhesive layer regarded as a cohesive zone, while enabling the enrichment of the model, making it more representative of the physical reality
Boundary layer transition over a lowreynolds number rotor : effects of roughness and freestream turbulence
Get PDFTwo separate experiments are conducted on a three
bladed NACA0012 rotor operating at low Reynolds numbers
using phase-locked infrared thermography coupled
with simultaneous force and torque measurements. The
first, focuses on the effects of freestream turbulence
on boundary layer transition over the suction side of
the aerofoil of the rotor in an advancing configuration.
Freestream turbulence (FST) was generated in an open
section wind tunnel using grids and was characterized using
Hot-Wire anemometry. In general, when the rotor
was subjected to FST, an increase in thrust and efficiency
was observed, which could be due to the FST suppressing
flow separation or by inducing early transition. The second
experiment, consisted of a parametric study on the
impact of forcing boundary layer transition using roughness
placed on the suction side of the aerofoil, in a hover
configuration. The height of the roughness was varied
from 52-220μm and was placed at all at at 10% chord,
over the entire span of the blade. Force and torque measurements revealed that there could be a optimal roughness height that could lead to a performance increase
Phase transformation of the Ti-5553 titanium alloy subjected to rapid heating
Get PDFThe α → β phase transformation upon heating in the Ti-5553 alloy with lamellar-nodular bimodal microstructure was tracked in situ with high energy X-ray diffraction. Rapid heating at 10, 50 and 100 °C s−1 from room temperature to 1050 °C was tested. Phase transformation on heating was studied by a combined analysis of the microstructural features that provides estimates of mass fractions, mean lattice parameters and full width at half maximum for the two phases. In comparison with equilibrium conditions, the experimental mass fractions reveal a shift of the transformation domain toward high temperatures when the heating rate increases. Also, the dissolution of the α phase is largely impacted by its morphology, the transformation being faster for α lamellae. The combined analysis of mean lattice parameters and full width at half maximum suggests that the α → β phase transformation on heating is diffusion controlled. The β phase therefore inherits the solute content of the adjacent parent α phase, leading to chemical heterogeneities in the β phase regardless of the heating rate
On the potential applications of acoustic emission in friction stir welding
Get PDFIn friction stir welding (FSW), only a few studies related to acoustic emission (AE) signals analysis have been conducted. In this work, the potential application of AEs in FSW is explored from a phenomenological and monitoring point of view. In static tests, with the tool only rotating without advancing, the information hidden behind AEs concerning the tool-workpiece interaction was investigated. Additionally, the sensors' positioning analysis is considered by comparing the signals' features obtained by placing the sensor on the welding plate or the support. Then in the second part, the effective capability of detecting internal defects during friction stir welding through AE signals monitoring is addressed. The experimental tests were performed on aluminum alloys of two different heat treatable families. Differences in the material plastic behavior depending on the aluminum alloys and the rotational speed were revealed by AEs features such as the amplitude and the absolute energy. In addition, internal defect occurrence was correlated with a shift in the signal centroid frequency. The results are auspicious for employing AE signals to deepen the tool-workpiece interaction and identify internal defects
Local Anodizing of a Newly Prepared Aluminum Micrometric Disk
Get PDFA search through the literature reveals that the vast majority of studies about aluminum anodizing were conducted at the macroscale (i.e., from cm2 up to m2), while those focused on local anodizing (i.e., on surfaces of less than 1 mm2) are rare. The last ones either used insulating masks or were conducted in an electrolyte droplet. The present study describes on the one hand a new way to prepare aluminum microelectrodes of conventional disk-shaped geometry, and on the other hand the local anodizing of their respective aluminum micrometric top-disks. The influence of the anodizing voltage on anodic film characteristics (i.e., thickness, growth rate and expansion factor) was studied during local anodizing. Compared with the values reported for macroscopic anodizing, the pore diameter appears to be significantly low and the film growth rate can reach atypically high values, both specificities probably resulting from a very limited increase in the temperature on the aluminum surface during anodizing
Improving the Estimation of the Wavenumber Spectra From Altimeter Observations
Get PDFSatellite altimeters provide sea-level measurements along satellite track. A mean profile based on the measurements
averaged over a time period is then subtracted to estimate
the sea-level anomaly (SLA). In the spectral domain, SLA is
characterized by a power spectral density (PSD) whose slope
in a log–log scale is a parameter of great interest for ocean monitoring. Estimation of this spectral slope is usually done through a cumulated periodogram using a large number of signal samples. The location and dates of the data induce the spatial and temporal resolution of the slope estimates. To improve this resolution, this article studies a new parametric method based on an autoregressive model combined with a warping of the frequency scale (denoted as ARWARP). This ARWARP model provides a PSD estimate, with a lower variance than the classical Fourier-based ones and is reliable in the case of a small sample number. To give a reference in the performance of the SLA slope estimation, the corresponding Cramér–Rao bound is derived. Then, rather than performing linear regression on the spectral estimates, a new estimator of the slope is suggested, based on a model fitting of the PSD. A statistical validation is proposed on simulated SLA signals, showing the performance of slope estimation using this ARWARP spectral estimator, compared to
classical Fourier-based methods. Application to Sentinel-3 real data highlights the main advantage of the ARWARP model,
making possible SLA slope estimation on a short signal segment, i.e., with a high spatial and/or temporal resolution
A data-driven framework for the deployment of urban air mobility
Get PDFNowadays, mobility in cities is becoming difficult due to demographic growth and the increasing need for on-demand services. As a response, megacities are looking into the possibility of introducing air mobility to reduce traffic congestion, provide quick answers to crises situations, etc. However, even though the key enabling technologies are mature (thanks to advances in energy efficiency, unmanned air engines, information and communication technologies, and other developments), some critical issues remain unresolved, placing additional pressure on public authorities to renew the existing solutions: - When it comes to implementing urban air mobility, what are the most significant obstacles and valuable insights to keep in mind (how to integrate air and land modes of transportation; are the current infrastructures ready to accommodate the air mode, etc.)? - Can the market viability sustain the required investments for the deployment? - What are the critical components of the resulting mobility system of systems? To answer these questions and facilitate the implementation of urban air mobility (UAM), in this thesis, we first conducted a bibliometric analysis to identify primary research areas and associated obstacles related to its implementation. Due to the lack of data on this hot research topic, we proposed a deep learning method to predict the UAM demand using a taxi-based benchmark dataset. The proposed solution is a hybridization of the transfer learning method with the transformer architecture. In order to assess the feasibility of the deployment, we proposed a data-driven framework that allows us to explain the critical components using a system engineering methodology. It can later assist decision-makers in developing decision-centric applications, such as predictions, infrastructure maintenance, service renewal, etc. Finally, we investigated the interoperability concerns of the main components in our proposed framework to facilitate communication between the existing solutions (which are mostly user-centric) and the components designed specifically for UAM operation. Future work intends to combine a discrete events-based method with artificial intelligence to simulate each component of the proposed framework and model different real-life scenarios
Wing Structural Model for Overall Aircraft Design of Distributed Electric Propulsion General Aviation and Regional Aircraft
Get PDFIn the context of reducing the environmental footprint of tomorrow’s aviation, Distributed Electric Propulsion (DEP) has become an increasingly interesting concept. With the strong coupling between disciplines that this technology brings forth, multiple benefits are expected for the overall aircraft design. These interests have been observed not only in the aerodynamic properties of the aircraft but also in the structural design. However, current statistical models used in conceptual design have shown limitations regarding the benefits and challenges coming from these new design trends. As for other methods, they are either not adapted for use in a conceptual design phase or do not cover CS-23 category aircraft. This paper details a semi-analytical methodology compliant with the performance-based certification criteria presented by the European Union Aviation Safety Agency (EASA) to predict the structural mass breakdown of a wing. This makes the method applicable to any aircraft regulated by EASA CS-23. Results have been validated with the conventional twin-engine aircraft Beechcraft 76, the innovative NASA X-57 Maxwell concept using DEP, and the commuter aircraft Beechcraft 1900