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Insights from the developement of humoristic Control cartoons for undergraduate students
No full textInternational audienceThe societal impact of Control on the young generation is one primary concern for the Control community and Control Education is a key factor. Presenting theoretical concepts on Control Engineering in an attractive way to engineering students, while remaining rigorous, is a challenge for the Control Education community. Therefore, this extended abstract focuses on the development of new Control cartoons for undergraduate students in CentraleSupélec, as part of the "FAnAuto" project. Some insights of this project toghether with feedback on the cartoons development phase are also shared.</div
Droplet concentration in water spray using short-range elastic backscatter lidar
No full textInternational audienceTo our knowledge, a novel experimental method is proposed to remotely measure the droplet concentration in a water spray using a short-range elastic backscatter lidar. A specific calibration technique is proposed to determine the lidar radiometric constant, enabling the conversion of lidar signals into attenuated backscatter signals and, ultimately, into aerosol properties, including average volume concentration. To our knowledge, a new formulation for the lidar constant is proposed, using the total spray transmittance and the particle size distribution of the water droplets, measured using the established laser diffraction technique. The lidar constant value is then compared and discussed in relation to an alternative method based on a Lambertian surface. Ultimately, the attenuated backscatter signals, calculated using the calibration constant, enable the estimation of the average volume concentrations of droplets in the spray under various injection conditions of a full-cone pneumatic atomizer. The retrieved concentrations range between 10 8 and 10 9 droplets per cubic meter, which are comparable to those obtained from laser diffraction measurements, especially for sprays with large droplets, i.e., with a Sauter mean diameter greater than 50 µm
Influence de certains paramètres sur la performance du contrôle de l'interaction choc/couche limite par paroi poreuse
No full textInternational audienceThis chapter examines the influence of hole diameter, porosity, thickness-to-diameter ratio, and stagger angle on the performance of porous bleed control in mitigating the negative effects of shock-wave/boundary-layer interactions. A detailed numerical study focuses on the control of an irregular shock reflection, or Mach reflection, where a separation bubble below the shock foot is present in the uncontrolled case. Implementing bleed control modifies the flow field significantly, with variations in bleed rates upstream and downstream of the shock because of the external flow characteristics. The findings indicate that smaller hole diameters enhance bleed efficiency and control effectiveness, while porosity levels and thickness-to-diameter ratios exhibit complex trends, with a medium thickness-to-diameter ratio and a stagger angle of 45° emerging as optimal configurations for effective shock-wave/boundary-layer control.Ce chapitre examine l’influence du diamètre des trous, du taux de porosité, du rapport épaisseur sur diamètre et de l'arrangement des trous sur la performance du contrôle de l'interaction onde de choc/couche limite par paroi poreuse. Une étude numérique détaillée a été réalisée sur le contrôle d’une réflexion de choc irrégulière, ou réflexion de Mach, pour laquelle un décollement en pied de choc est présent dans le cas non contrôlé. Le contrôle par paroi poreuse modifie considérablement l'écoulement, avec des variations du débit aspiré en amont et en aval du choc à cause des caractéristiques de l'écoulement externe. Les résultats indiquent que des trous plus petits améliorent l’efficacité du contrôle, tandis que l'effet du taux de porosité et du rapport épaisseur sur diamètre présente des tendances complexes, avec une valeur moyenne du rapport épaisseur sur diamètre et un angle d'arrangement de 45° qui apparaissent comme la configuration optimale pour un contrôle efficace de l'interaction onde de choc / couche limite
Extending the machine-learned optimised stable Taylor-Galerkin scheme to solve the Burgers' equation
No full textInternational audienceThis study offers a Fourier error analysis of the Two-step Taylor Galerkin scheme for Burgers’equation. It reveals new insights into the complex interplay between the numerical error and thenon-linearity using the spectral model of Burgers’ energy cascade. The analysis emends the popularperception of the role of artificial dissipation towards numerical stability at a shock. In addition,new insights on shock sensors from a spectral standpoint are presented to motivate the need forphysics-based shock sensors. Based on these findings, an extension to the Machine Learned TwostepTaylor Galerkin scheme (ML-TTGC) developed in previous work is proposed to solvethe non-linear Burgers’ equation. The proposed scheme generalises to a wide range of problemsoutside of training and maintains stability and accuracy even on irregular meshes
A High-Order p-adaptive Algorithm for Large-Eddy Simulation Based on a Discontinuous Galerkin Method
No full textInternational audienceThe aim of this paper is to present and analyse a static p-adaptation algorithm based on a modal high-order discontinuous Galerkin method. To this end, we first define appropriate error estimation strategies that provide information on the necessary time-independent local resolution quality. Two error indicators are employed, the Small-Scale Energy Density (SSED) indicator proposed in Naddei (2019) and the novel Small-Scale Lifted (SSL) indicator developed in this work. Based on the SSED estimator, three different strategies are considered to extend these indicators to perform static padaptive simulations of unsteady flow problems. The first approach consists in applying the SSED estimator to the time-averaged solution (SSED-A). The second and third approaches consist in evaluating the temporal L 2 and L ∞ -norms of the indicator computed from the instantaneous solution, called respectively L 2 -SSED and L ∞ -SSED. These strategies are compared by performing simulations of the periodic laminar flow past a cylinder at Re = 100 and Mach = 0.1, and of the turbulent flow over periodic hills at Re = 2 800. The outcome from these computations shows that the best performance is achieved when the L ∞ -SSED indicator is used. Finally, the developed adaptation algorithm is applied to the LES of the transitional flow past a NACA0012 airfoil at Re = 50 000 and α = 5 • using the L ∞ -SSED and the L ∞ -SSL indicators. It is shown that the use of the SSL indicator provides improved results as compared to the SSED indicator. The results presented in this paper demonstrate that the use of p-adaption improves the quality of under-resolved turbulent flow simulations for a similar computational cost as compared to p-uniform simulations
Hybrid Laminar Flow Control Investigation of Microperforated Skin With Variable Porosity Suction Device
No full textInternational audienceReduction of the specific consumption of aircraft would lead to substantial economic and environmental benefits. A promising technique consists in reducing skin friction drag by delaying the laminar-turbulent transition point as far aft as possible, particularly on the wings, in order to obtain lower friction coefficient in the presence of laminar flow. This can be achieved by Hybrid Laminar Flow Control (HLFC) technology. This paper presents the windtunnel tests of a large-scale HLFC wing model conducted in ONERA’s S1MA wind-tunnel. The wing model is designed to investigate the efficiency of a variable porosity microperforated titanium suction cartridge and to assess the attachement line contamination phenomena
Attention Guidée par la Segmentation pour la Réponse Automatique à des Questions Visuelles à partir d'Images de Télédétection
No full textInternational audienceAttention Guidée par la Segmentation pour la Réponse Automatique à des Questions Visuelles à partir d'Images de Télédétectio
Suppression des oscillations induites par les chocs d'un panneau souple avec des matériaux viscoélastiques
No full textInternational audienceThe influence of structural viscosity on the fluid–structure interaction between a normal shock-wave and a compliant panel is investigated. Two compliant panels are designed to allow significant static deformation while exhibiting different dynamic behaviors. For this purpose, two distinct elastomeric materials are used based on their dynamic responses within the shock oscillation frequency range: polyurethane 40A for the elastic panel and Tango Polyjet 61A for the viscoelastic panel. Dynamic mechanical analyses characterize the materials’ dynamic properties, enabling the evaluation of natural vibration modes and frequencies of both structures. The elastic panel exhibits natural vibration frequencies that align with the ones of the natural oscillations of the shock-wave. Wind-tunnel experiments reveal strong dynamic coupling between the elastic panel and the shock-wave, leading to large-amplitude, synchronized oscillations when the shock is centered on the panel. In contrast, the viscoelastic panel is designed to avoid the fluid–structure coupling observed in the elastic panel. The marked viscoelastic properties of the material shift the natural vibration modes to higher frequencies, outside the shock-wave’s natural oscillation range. As a result, in its interaction with the shock-wave, the viscoelastic panel exhibits only a large static deformation – greater than that of the elastic panel – without any dynamic fluid–structure coupling, regardless of the shock position. These findings demonstrate that viscoelastic materials hold significant potential for flow control applications, providing structural damping and frequency-dependent stiffening, which effectively decouple static deformation from dynamic interaction. Our results suggest that viscoelastic panels could be optimized as adaptive bumps for shock control, responding to fluid dynamics without inducing unwanted dynamic coupling.L'influence de la viscosité structurelle sur l'interaction fluide-structure entre une onde de choc normale et un panneau souple est étudiée. Deux panneaux souples sont conçus pour permettre une déformation statique importante tout en présentant des comportements dynamiques différents. Pour ce faire, deux matériaux élastomères distincts sont utilisés sur la base de leurs réponses dynamiques dans la gamme des fréquences d'oscillation des chocs : le polyuréthane 40A pour le panneau élastique et le Tango Polyjet 61A pour le panneau viscoélastique. Des analyses mécaniques dynamiques caractérisent les propriétés dynamiques des matériaux, permettant l'évaluation des modes et fréquences de vibration naturelle des deux structures. Le panneau élastique présente des fréquences de vibration naturelle qui s'alignent sur celles des oscillations naturelles de l'onde de choc. Les expériences en soufflerie révèlent un fort couplage dynamique entre le panneau élastique et l'onde de choc, conduisant à des oscillations synchronisées de grande amplitude lorsque le choc est centré sur le panneau. En revanche, le panneau viscoélastique est conçu pour éviter le couplage fluide-structure observé dans le panneau élastique. Les propriétés viscoélastiques du matériau déplacent les modes de vibration naturelle vers des fréquences plus élevées, en dehors de la plage d'oscillation naturelle de l'onde de choc. Par conséquent, dans son interaction avec l'onde de choc, le panneau viscoélastique ne présente qu'une importante déformation statique - supérieure à celle du panneau élastique - sans aucun couplage dynamique fluide-structure, quelle que soit la position du choc. Ces résultats démontrent que les matériaux viscoélastiques présentent un potentiel important pour les applications de contrôle des écoulements, en fournissant un amortissement structurel et un raidissement dépendant de la fréquence, qui découplent efficacement la déformation statique de l'interaction dynamique. Nos résultats suggèrent que les panneaux viscoélastiques pourraient être optimisés en tant que bosses adaptatives pour le contrôle des chocs, répondant à la dynamique des fluides sans induire de couplage dynamique indésirable
Structured Gaussian Process Regression for Multiphysics Problems
No full textInternational audienceIn addition to other multi-query problems, global optimization of design variables in multi-physics engineering problems requires the resolution of coupled systems of equations for many sets of design variables. Such coupled systems are often resolved using the partitioned approach, whereby each individual system of equations is solved separately using its numerical scheme, and the coupling equations are enforced through fixed point iteration. This optimization procedure can be made more efficient by using, for example, Gaussian Process based surrogate models. Gaussian Processes are attractive for this purpose, since they are flexible, have a strong theoretical foundation and the variance of the Gaussian Processes can be used to estimate the uncertainty of the surrogate solution. This estimate can be used to improve the accuracy of the surrogate model in areas of the parameter space where it is inaccurate. Previous work has explored the potential of applying this procedure to each distinct system of equations separately, and calculating the distribution of the solutions of the resulting coupled system through fixed point iteration of the sample paths of the Gaussian Processes. This algorithm was successfully used in Bayesian and gradient-based optimization. Conversely, the Gaussian Process modelling framework has recently been extended to handle various types of constraints. Novel strategies have been developed to ensure that Gaussian Process sample paths be, for example, monotonic, or convex. Constraining Gaussian Process sample paths to satisfy a given PDE has also been a popular line of inquiry. The aim of the present work is to extend these results concerning structured Gaussian Processes to the multiphysics case. First of all, ways for increasing the regularity of the Gaussian Process sample paths are investigated, with the objective of ensuring that the sample paths of the Gaussian Processes satisfy certain conditions that the solutions of the PDEs are known to satisfy. Certain strategies from the physics-constrained Gaussian Process literature are extended to the multiphysics case. Finally, we present some theoretical results concerning our work, and discuss and compare our work with others in the literature
Conceptual Co-Design of Cryogenic Storage and Ballast Systems for a Hydrogen Airliner
No full textInternational audienceHydrogen is nowadays regarded as one of the possible replacements for kerosene as the main fuel for the aviation sector. However, its very low density at ambient conditions is a significant limitation that requires novel onboard fuel storage technologies to be developed. This article presents results of a conceptual study on a Liquid Hydrogen (LH2) storage system for the rear fuselage of Short/Medium Range (SMR) airliner, conducted in the frame of the EU-funded ACAP research program. A structural optimization of the tank geometry is used to assess the effects of the gravimetric index on the mass and dimensions of the storage system. The extracted models are implemented in mass and center-of-gravity (CG) calculations used for the design of four potential ballast configurations, used to control the CG range within acceptable limits. A top-level performance optimization of each aircraft configuration is performed based on a flight probability density function describing the aircraft’s expected mission requirements: The results of this analysis are detailed and discussed. Finally, conclusions are presented on the feasibility, advantages and disadvantages of different tank/ballast system configurations for the LH2 SMR airliner