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International audience; Nowadays, experimental analyses of fluid-structure interactions on flexible rotating blades are few widespread. For this purpose, an experimental rotor test bench for blades with variable flexibility is under development. Different sets of blades have been fabricated with different composite materials and variable thickness, depending on the number of layers considered.The main objective of the present work is to estimate which sets of blades are more sensitive to flutter occurrence based on their Campbell diagrams. For this purpose, a finite element approach is developed to model the dynamic behavior of the blades assumed as a uniform, slender, isotropic and homogeneous beam with out-of-plane bending and torsion deformations, submitted to inertial and centrifugal forces due the rotation effects. Two numerical models were developed by considering Timoshenko and Euler-Bernoulli beam theories; both are validated by means of the software COMSOLr. Later, the mechanical properties of each set of blades have been identified from the frequency response functions (FRFs) obtained through experimental vibration tests. The frequencies and eigenmodes of blades determined experimentally are compared with those obtained with FEM model. Then, rotation effects on the blade frequencies are studied by using Campbell diagrams for all set of blades studied. It is evidenced for some of the sets the presence of intersections between bending and torsional frequencies in the interval of the operational rotating speed of the test bench. This fact might be considered as an indicator of potential flutter occurrence.Aerodynamic load will be consider in the future work.

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International audience; With stratospheric flight ormartian exploration in perspective, the compressibility influence on thewake dynamics ofa NACA0012 profile is investigated. The unsteady flow past the airfoil at Re = 1000 is characterized using directnumerical simulations for various angles of attack α ∈ [0°; 20°] and Mach numbers up to M∞ = 0.5. Steady flowsobtained using the selective frequency damping (SFD) technique are used as base states for a global linear stabilityanalysis. The influence of both the angle of attack and the Reynolds number on the most amplifiedmode characteristicsis first investigated in the incompressible regime. Then, the compressibility effects in the subcritical regime areconsidered. A stabilizing or a destabilizing effect of compressibility is observed depending on the angle of attack andtheReynolds number. For α < 20°, compressibility has a destabilizing effect close to the critical threshold,which resultsin anearlierHopfbifurcation,whereas increasing theMach number always results in a decrease of the growth rate of themode well above the critical threshold. Finally, the mode frequency decreases with the Mach number.

International audience; During the pullout maneuver, peregrine falcons were observed to adopt a succession of specific flight configurations that are thought to offer an aerodynamic advantage over aerial prey. Analysis of the flight trajectory of a falcon in a controlled environment shows it experiencing load factors up to 3g, and further predictions suggest this could be increased up to almost 10g during high-speed pullout. This can be attributed to the high maneuverability promoted by lift-generating vortical structures over the wing. Wind-tunnel experiments on life-sized models in the different configurations together with high-fidelity computational fluid dynamics simulations (large-eddy simulations) show that deploying the hand wing in a pullout creates extra vortex lift, which is similar to that of combat aircraft with delta wings. The aerodynamic forces and the position of the aerodynamic center were calculated from the simulations of the flow around the different configurations. This allowed for an analysis of the longitudinal static stability in the early pullout phase, confirming that the falcon is flying unstably in pitch with a positive slope in the pitching moment and a trim angle of attack of about 5 deg, which is possibly to maximize responsiveness. The hand wings/primaries were seen to contribute to the augmented stability, acting as “elevons” would on a tailless blended-wing/body aircraft.

International audience; Recent successful recovery techniques for rockets require that rockets maintain a vertical configuration with zero vertical and lateral velocities; otherwise, landings may fail. To relax this requirement, a new active-arresting system (inspired by the arresting gears used on aircraft carriers) is proposed herein to achieve a robust landing, even if the rocket deviates from the target position or has notable residual velocities and inclinations. The system consists of four deployable onboard hooks above the rocket’s center of mass, an on-ground apparatus containing four arresting cables forming a square capture frame, and four buffer devices to actively catch and passively decelerate the landing rocket. To catch the rocket, the capture frame was controlled by servo motors via a simple proportional–derivative controller. After catching, the buffer devices generate decelerating forces to stop its motion. A flexible multibody model of the proposed system was built to evaluate its robust performance under various combinations of multiple uncertainties, such as noise measurement, time delay in the motor, initial conditions, and wind excitation. Using a quasi-Monte Carlo method, hundreds of deviated landing cases were generated and simulated. The results confirmed the robustness of the proposed system for achieving successful terminal landings.

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International audience; Hybrid-electric aircraft are a potential way to reduce the environmental footprint of aviation. Research aimed at this subject has been pursued over the last decade; nevertheless, at this stage, a full overall aircraft design procedure is still an open issue. This work proposes to enrich the procedure for the conceptual design of hybrid aircraft found in literature through the definition of a multidisciplinary design optimization (MDO) framework aimed at handling design problems for such kinds of aircraft. The MDO technique has been chosen because the hybrid aircraft design problem shows more interaction between disciplines than a conventional configuration, and the classical approach based on multidisciplinary design analysis may neglect relevant features. The procedure has been tested on the case study of a single-aisle aircraft featuring hybrid propulsion with distributed electric ducted fans. The analysis considers three configurations (with 16, 32, and 48 electric motors) compared with a conventional baseline at the same 2035 technological horizon. To demonstrate the framework’s capability, these configurations are optimized with respect to fuel and energy consumption. It is shown that the hybrid-electric concept consumes less fuel/energy when it flies on short range due to the partial mission electrification. When one increases the design range, penalties in weight introduced by hybrid propulsion overcome the advantages of electrified mission segment: the range for which hybrid aircraft have the same performance of the reference conventional aircraft is named the “breakdown range.” Starting from this range, the concept is no longer advantageous compared to conventional aircraft. Furthermore, a tradeoff between aerodynamic and propulsive efficiency is detected, and the optimal configuration is the one that balances these two effects. Finally, multiobjective optimization is performed to establish a tradeoff between airframe weight and energy consumption.

International audience; Acoustic liners are specific devices dedicated to reduce noise pollution of aircraft. They contained a large number of cavities which are submitted to a turbulent grazing boundary flow. In some cases, the shear layer can become unstable, and couples with the acoustic waves propagating in the cavity, leading to a strong vortex-noise interaction. Whereas this vortex-noise coupling is well known in single-cavity configurations where the boundary layer can be described by its upstream characteristics, the interaction between a turbulent grazing flow and multiple cavities is less understood, mainly because the boundary layer may evolve along the liner. This study investigates numerically the coupling between acoustic waves and hydrodynamic fluctuations in an academic liner configuration containing multiple deep cavities. First a single 3D cavity is simulated using LES, revealing a strong vortex-noise coupling at the frequency of the quarter-wave mode at 750Hz, due to a shear layer instability with a wavelength shorter than the cavity width. Then, both a 2D and 3D configuration containing 101 cavities are computed and analyzed. When the acoustic feedback loop is cut off, no vortex-noise coupling occurs, however large flow structures can be observed in the boundary layer. When switching on the acoustic feedback loop, the vortex-noise coupling at 750Hz is again present, yet a more complex noise spectrum is obtained. In particular, lower frequencies are observed, associated to intermittency due to the desynchronization between cavities. Moreover, it is shown that the boundary layer evolves along the liner. One key phenomenon is the massive instability of the turbulent boundary layer, generating large coherent structures with a wavelength larger than the cavity width in the downstream part of the liner. A scenario is then proposed to explain this competition between these two phenomena: in the upstream part of the liner, the flow is dominated by the vortex-noise coupling at 750Hz. Further downstream, however, the shear layer becomes thicker, and is therefore more robust to transverse acoustic excitation, leaving the place for the large turbulent flow structures in the boundary layer to dominate the flowfield.

International audience; Reducing fuel consumption is a major driver for the design of future aircraft. The engine integration primary structure plays a significant role in the integrated engine thrust-specific fuel consumption. A topology optimization framework was developed to design the primary structure integrating the engine to the aircraft wing considering mass, stress, and engine performance criteria. The proposed approach had to address several challenges associated with the use of nonuniform meshes, the integration of the engine model as a super-element, and the presence of nonconforming mesh interfaces. Analytical adjoint evaluations for all the responses were also derived. The framework was tested on a simplified engine model providing a consistent solution.

International audience; The measurement of air density in the Earth’s thermosphere has a wide range of scientific applications from space weather to upper Atmosphere dynamics, but also technical applications from satellite control to predictions of atmospheric reentry of space debris. This study models the torques applying on a three-unit CubeSat in low Earth orbit to infer the capability of such platforms to measure the air density along their orbit. Realistic noise levels of available CubeSat components are used, and sensitivity to the various noise sources is presented. The precise knowledge of the spacecraft attitude, angular acceleration, residual magnetic dipole, and center of gravity is critical to allow proper air density retrieval. Winds in the thermosphere also have a significant impact on the thermosphere density retrieval, suggesting that this Parameter can also be constrained. Attitude control is not necessary if the attitude itself is properly known. The application to the EntrySat CubeSat predicts that such retrieval is possible at altitudes lower than 200 km with errors lower than 30%. The air density retrieval from CubeSat platforms will open new capabilities to infer upper atmosphere dynamics.

International audience; The present investigation targets the generation of airfoil trailing-edge broadband noise that arises from the interaction of turbulent boundary layer with the airfoil trailing edge. Large-eddy simulations, carried out using a massively parallel compressible solver CharLESX, are conducted for a Controlled-Diffusion (CD) airfoil with rounded trailing edge for seven configurations, characterized with a Reynolds number, angle of attack and Mach number. An analysis of the unsteady pressure signals in the boundary layer is proposed in regard to classical trailing edge noise modelling ingredients.

This work aims to facilitate deployment of novel distributed space systems architectures such as Federated Satellite Systems (FSS). In particular, the purpose of the work is to identify retrofitting possibilities to incorporate existing satellites into a network. For the satellite case, the paper presents a systematic review of possible retrofitting options such as direct modifications, which include replacement and addition of interfaces, and indirect modifications with adding an intermediary (FSS Negotiator). While the paper concludes that direct modifications of existing satellites are non-feasible from the technical point of view, it also identifies a possible scenario of retrofitting by adding as an intermediary a Negotiator satellite. The link budget for the inter-satellite link between an existing satellite mission such as SPOT-6 and FSS Negotiator was estimated. The work concludes that from the link budget point of view with the existing communication technologies such configuration can provide a slant range limited from several hundred to thousands kilometers. Through analysis of open data of satellite characteristics, including ITU information concerning planned or existing space stations, the work comes up with several models for the further trade-off analysis, identifying how parameters of FSS Negotiator such as an operated bandwidth and frequency, types of supported modulations and cumulative throughput correlate with the covered number of satellites. These results might be used for the tradeoff analysis for the FSS Negotiator mission design. Eventually paper proposes several possible FSS Negotiator architectures and its high-level technical requirements based on analysis of characteristics of existed and planned satellites.

International audience; Recent research is showing growing interest in low-power electromechanical de-icing systems and, in particular, de-icing systems based on piezoelectric actuators. These systems use the vibrations generated by piezoelectric actuators at resonance frequencies to produce shear stress at the interface between the ice and the support or to produce tensile stress in the ice. This paper provides analytical and numerical models enabling a better understanding of the main de-icing mechanisms of resonant actuation systems. Different possible ice-shedding mechanisms involving cohesive and adhesive fractures are analyzed with an approach combining modal, stress, and crack propagation analyses. Simple analytical models are proposed to better understand the effects on ice shedding of the type of mode, ice thickness, or frequency with respect to cohesive and adhesive fractures.

International audience; Control architecture sizing is a main challenge of blended-wing–body design. This aircraft configuration typically features redundant elevons located at the trailing edge of the wing, acting simultaneously on pitch and roll axes. Consequently, a proper sizing requires one to consider coupled longitudinal and lateral criteria. Moreover, significant hinge moments due to large control surface areas, combined with high deflection rates in order to safely control the longitudinal instability, may result in excessive power consumption and actuator mass penalty. Therefore, it is highly desirable at the preliminary design level to minimize control surface areas, while ensuring adequate closed-loop handling qualities, with limited deflections and deflection rates. The problem of integrated design of control surface sizes and flight control laws for an unstable blended-wing–body aircraft is addressed here. The latest tools for H∞ nonsmooth optimization of structured controllers are used to optimize in a single step the gains for both longitudinal and lateral control laws, as well as a control allocation module, while minimizing the control surface span. The following constraints are ensured: maximal deflection angles and rates for 1) pilot longitudinal pull up, 2) pilot bank angle order, and 3) longitudinal turbulence. Using this coupled approach, significant gains in terms of the outer elevon’s span as compared to the initial layout are demonstrated, whereas closed-loop handling quality constraints are guaranteed.

International audience; In the field of Aircraft Design, new transport concepts rely heavily on aero-propulsive effects with the objective of providing step changes in terms of energy consumption. Given the strong dependency of the level of lift with respect to engine settings, there is an added value for the designers to complete full simulations of the operational mission to verify the viability of the selected architecture. Regarding Air Traffic Management, the need for more accurate trajectories as well as solutions to characterize new aircraft in the air space has been identified. Taking the opportunity of these shared requirements, the authors present in this paper the coupling between a conceptual design sizing tool and an ATM simulator. The objective is to pave the way for future optimizations of the global system where aircraft would be designed taking into account real flight routes defined by ATM constraints. To validate the simulation model generated by the sizing code, resulting climb trajectories as well as initial cruise phases are compared with real flight traces recorded with an ADS-B antenna.

International audience; In the field of aircraft design, the last few decades have focused on the iterative improve- ment of conventional tube-and-wing designs to reduce cost, noise, and emission. Never- theless, the growing expectation in terms of environment impact for the next generation of aircraft pushes for more radical changes in the design. For unconventional aircraft configurations, the need to integrate more accurate data coming from higher fidelity analysis earlier in the design process becomes more and more necessary. However, high-fidelity tools require long computation times and usually are associated with high-dimensional problems, both in terms of design variables and constraints. Therefore, these optimizations are often done at higher computational cost (gradient-based algorithms) in order to decrease the number of necessary function evaluations. In addition, the use of the adjoint method is often implemented to accurately and efficiently compute derivatives for large numbers of design variables. At the same time, new methods have been investigated to obtain opti- mized configurations at a reasonable computational cost. The work presented in this paper focuses on SEGOMOE algorithm, a solution to tackle this kind of optimization process of complex design problem through the use of an enrichment strategy approach based on mixture of experts surrogate models. Two aerodynamic shape optimization test cases, derived from cases developed by the Aerodynamic Design and Optimization Discussion Group (ADODG) are addressed: one with a single global minimum, and another one with several local minima. Both problems are nonlinearly constrained problems that involve a large number of design variables. Results are compared to gradient-based optimizers. A hybrid approach combining the advantages of both SEGOMOE and gradient-based optimization is proposed and evaluated to reduce the number of function evaluations and to ensure the convergence to the global optimum.

International audience; A series of new bi-stable fluidic oscillators which can generate discrete pulsed jets in a wide frequency range (50-300Hz) with maximum velocities of the order of 200 m/s have been developed for flow separation control purposes. A preliminary experimental analysis of the prototypes has been performed thanks to a pressure sensor and the results have shown that the oscillation frequency has a nearly linear relationship with the length of its feedback loops. Thus, a new function is proposed to estimate the oscillation frequency according to the experimental results. In addition, numerical simulations are carried out in order to better understand the jet switching mechanism inside the oscillator and identify the parameters controlling the dynamics of these oscillations. Finally, it is verified that the switching process of the main jet is not only controlled by the pressure difference between the two control nozzles, but also by the pressure difference between the two main branches of the oscillator. This new finding will be of great help in future design of this kind of fluidic oscillators.

International audience; This paper proposes a concept of navigation and guidance strategy planner for urban operation of a VTOL-type UAV. One of major challenges of UAV autonomous navigation in an urban environment is to deal with the risk of GPS signal occlusion. In order to address this issue, various approaches have been proposed for GPS-independent UAV navigation and guidance such as visual odometry and visual servoing control. In this context, this work supposes that different navigation and guidance modes using different set of sensors are available onboard an UAV. An idea of the proposed planner is to anticipate the navigation and guidance performance degradation (or amelioration) due to unavailability (or availability) of certain mode in the path planning task. The planning problem is formulated as a 5D (3D position + selection of navigation and guidance modes) graph search problem, where the localization and path execution uncertainties are propagated according to a model of corresponding modes for each node transition. Node transition is denied if the path execution uncertainty ellipsoid intersects with any obstacle. A minimizing cost function is defined by a volume of the path execution uncertainty corridor, as it implies minimizing path distance and execution accuracy at the same time. A deterministic graph search algorithm is applied to find a flight path with specified navigation and guidance mode transitions which minimizes the defined cost function. Simulations are performed by using path planning configurations given in an existing UAV obstacle field navigation benchmark, and the results are presented to prove the proposed navigation and guidance strategy planning concept.

International audience; This paper extends Froude’s momentum theory for free propellers to the analysis of shrouded rotors. A one-dimensional analytical approach is provided, and a homokinetic normal inlet surface model is proposed. Formulations of thrusts and power for each system component are derived, leading to the definition of optimum design criteria and providing insight into the global aerodynamics of shrouded rotors. In the context of micro-air vehicles applications, assessment of the model is conducted with respect to numerical data. Overall, comparison between numerical and analytical results shows good agreement and highlights the sensitivity of the model to viscous effects.

SINCE the seminal work of Powell in 1953 [1], it has been shown that jets impinging on a flat plate can generate intense acoustic tones in some cases. These tones are due to an aeroacoustic feedback loop mechanism composed of aerodynamic disturbances convected downstream and acoustic waves propagating from the flat plate to the nozzle. Several experiments have investigated the properties of this feedback mechanism. In the subsonic regime, Ho and Nosseir [2] and Nosseir and Ho [3] studied impinging round jets with different nozzle exit Mach numbers ranging from 0.3 up to 0.9. This allowed the authors to develop a model of the aeroacoustic feedback loop predicting the frequencies of the tones. In the supersonic regime, several researchers studied the feedback loop mechanism with, among others, Krothapalli et al. [4], Henderson et al. [5], Risborg and Soria [6], and Mitchell et al. [7]. In some cases, a feedback mechanism similar to that encountered in subsonic jets was obtained. In addition, this feedback loop mechanism was observed to occur very often when the jets were ideally expanded but with less occurrence and only for certain nozzle-to-plate distances when they were not. To better understand why a supersonic impinging jet is likely

Over the past twenty years, the commercial air transportation industry has witnessed many advances in technology as well as changes in fleet characteristics. Most new technologies have worked to reduce the cost of air travel, primarily through reductions in fuel consumption. Other changes like increased range, reduced crew requirements, and lower prices have simultaneously made air travel cheaper and more available. It is therefore of interest to understand how these changes have affected the welfare of the air transportation industry. Using causal modeling, this paper attempts to quantify the effects of these changes on the welfare the three main stakeholders of commercial aviation: aircraft manufacturers, airlines, and the public. We find that changes in the physical characteristics of the utilized fleet have influential causal effects on airline and manufacturer welfare. Additionally, we observe that these physical characteristics are themselves influence by manufacturer welfare, fuel prices, and aircraft value. We consider that the causal modeling methods used in this paper are useful for determining complex relationships between decision makers in the commercial avaiation industry, and that understanding these relationships is important in making decisions about future research and design activities. 1 Graduate student, Mechanical and Aerospace Engineering, +1 (360) 904-8972, gcwaycaster@ufl.edu. Student Member AIAA. 2 Distinguished Professor, Mechanical and Aerospace Engineering department,+1 (352) 392-9595, haftka@ufl.edu. Fellow AIAA. 3 Associate Professor, Mechanical and Aerospace Engineering department, +1 (352) 846-0665, nkim@ufl.edu. Associate Fellow AIAA. 4 Senior Lecturer, Newcastle Business School, +44 (191) 227-3465, volodymyr.bilotkach@newcastle.ac.uk 5 Assistant Professor, UPS, INSA, Mines Albi, ISAE; ICA (Institut Clement Ader), +33 (0)5 61 55 60 36, christian.gogu@univ-tlse3.fr. Member AIAA. 6 Professor, UPS, INSA, Mines Albi, ISAE; ICA (Institut Clement Ader), +33 (0)5 61 55 60 36, christian.bes@univtlse3.fr. Member AIAA.

International audience; In this communication we shall focus on the main governing equations and building blocks of the M.A.D (Anti-icing Deicing Modelling) numerical tool, which is now renamed as INUIT (Integrated NUmerical model of Ice protection sysTems) and part of the new generation of ONERA icing codes. The code simulates the functioning of an electro-thermal de-icing system. We shall also discuss the various improvements and new features we have added, especially a mechanical model of the ice block in order to improve the ice-shedding criterion.

This communication proposes to combine non causal modeling, metamodeling and scaling laws in order to take advantage of the inverse simulation capabilities of recent system level simulation software with the main target to assess technological alternatives quantitatively from a limited set of required data. The scaling laws are illustrated here for major hydraulic components (hydraulic cylinders and pumps) and are validated with manufacturers’ data. The proposed methodology is illustrated with the preliminary sizing of an electro-hydrostatic actuator driving an aircraft primary flight control surface (aileron). The design exploration for geometrical integration and mass is realized using to surface response models.

Evidence theory is one of the approaches designed s pecifically for dealing with epistemic uncertainty. While multiple approaches for propagating epistemic uncertainty through onedimensional functions have been proposed, propagation through multidimensional functions received less attention. Such propagation is partic ularly important when the multiple function outputs are not independent. The present paper proposes various algorithms for calculating belief and plausibility measures by unc ertainty propagation through multidimensional functions. A general approach is f irst presented followed by approaches in cases where the function is convex or linear over e ach focal element. An analytical example illustrates the importance of considering the funct ion output together when they are not independent. An application example to preliminary design of a propeller aircraft then illustrates the proposed algorithms for the convex and the linear cases. While the linear case is only an approximate method in this example it st ill found the exact results here.

Recently, there has been a growing interest for mixed categorical meta-models based on Gaussian process (GP) surrogates. In this setting, several existing approaches use different strategies. Among the recently developed methods, we could cite: GP models built using continuous relaxation of the variables, Gower distance based models or GP models derived from direct estimation of the correlation matrix. In this paper, we present a kernel-based approach that extends continuous Gaussian kernels to handle mixed-categorical variables. The proposed kernel leads to a GP surrogate that generalizes continuous relaxation and Gower distance based GP models. The good potential of the proposed framework is shown on analytical mixed-categorical variables test cases. On different settings, our proposed GP models is as accurate as the state-of-the-art GP models.

Aircraft operational performance is one of the key drivers to airline profitability and punctuality. Along with safety and technical performance, aircraft operational performance needs to be projected from the early stages of development to design an aircraft that can fully meet the expectations of airlines and passengers. The ability of a system to meet its operational requirements in terms of reliability, availability and costs is termed as ‘Operability’. This paper proposes a method to model the operability of an aircraft during early design and use it to predict its operational performance. Initially, in-service data is used to create a reference baseline for a system of interest. For a new design, the designers evaluate the changes (deltas) in terms of few high-level metrics from an operations point of view called Consolidated Operability Metrics. An operability model is developed using Bayesian networks that is then used to project the changes in operational performance of the new design in comparison to the baseline. This method will help aircraft architects in conducting trade-off studies during early design from an operational point of view.

In this paper, a characterization of a low Reynolds number two-bladed rotor in interaction with a beam is performed using both an experimental campaign performed in an anechoic room and implicit large eddy simulations (iLES) associated with the Ffowcs-Williams and Hawkins (F-WH) analogy. The rotor studied has a NACA0012 blade section profile extruded in the radial direction with a constant chord of 25 mm, a constant pitch of 10 and a diameter of 200 mm. This rotor is tested in interaction with 3 cylindrical beams of different diameters positioned at a distance of 20 mm below the rotor disk plane. The blade passing frequency (BPF) and the high frequency broadband noise appear to not be affected by the presence of the beam. On the contrary, the magnitude of the 2 BPF to 15 BPF harmonics increases up to 30 dB compared to the case without beam. For the dominant harmonics of the BPF, a dipole like pattern aligned with the beam can be observed. Numerical simulations were successfully validated against the experimental data for the dominant BPF harmonics and were then used to study the contribution of the rotor and the beam to the noise radiated. It is found that the beam is responsible for the increase in BPF harmonics and their characteristic directivity pattern.

The environmental impact of civil aviation at low altitudes concerns local air quality, the contribution to global warming and noise nuisances in residential areas located in the vicinity of airports. Aviation is responsible for only a small percentage of man-made CO2 and has a marginal impact on global warming compared to other sources, but the continuous growth of air traffic requires sustainable development to increase, creating economic value with less environmental impact. This research, integrated in the European JTI project Clean Sky, addresses the study of flight departure procedures that minimize the environmental impact of a single aircraft. Departure procedures minimizing perceived noise, the emission of nitrogen oxides and the contribution to the global production of carbon oxides are calculated. From an operational viewpoint, airlines will assign a different priority to each objective and the onboard calculator will provide the most environmental-friendly take-off flight path. These operational constraints entail that the designed algorithm must provide smooth and robust optimal flight paths.

International audience; Two- and three-dimensional modes developing on a steady spanwise-homogeneous laminar separated flow over a NACA 4412 airfoil have been numerically investigated using global linear stability theory. Considering variations of both the Reynolds number and the angle of attack, the two-dimensional von Kármán mode results to be always the leading mode since for all conditions examined it is more unstable than the three-dimensional von Kármán modes and the three-dimensional stationary modes, associated with the formation on the airfoil surface of large-scale separation patterns akin to stall cells. Sensitivity of the global modes is investigated numerically through adjoint-based methods in order to predict regions of the flow which are most sensitive to a modification of the base flow and the application of a steady force. Interestingly, the instability’s growth rate sensitivity function displays an extended region upstream of the separation bubble wherein a streamwise oriented force has a net stabilizing effect. Aerodynamic performances can thus be possibly improved by leveraging the boat-tailing effect induced by tangential jet actuators localized in this particular region of the flow

International audience; The paper introduces the EU funded project CS2-U-HARWARD, started, in response to the call JTI-CS2-2019-CFP10-THT-07: Ultra-High Aspect ratio wings, aiming at the use of innovative aerodynamic and aeroelastic designs in a multi-fidelity multi-disciplinary optimal design approach to facilitate the development of Ultra-High aspect ratio wings for medium and large transport aircraft. The structure of the project, the main goals as well as the preliminary results obtained together with the due final considerations are reported.

A new multifidelity method is developed for nonlinear orbit uncertainty propagation. This approach guarantees improved computational efficiency and limited accuracy losses compared to fully high-fidelity counterparts. The initial uncertainty is modeled as a weighted sum of Gaussian distributions whose number is adapted online to satisfy the required accuracy. As needed, univariate splitting libraries are used to split the mixture components along the direction of maximum nonlinearity. Differential Algebraic techniques are used to propagate these Gaussian kernels and compute a measure of nonlinearity required for the split decision and direction identification. Taylor expansions of the flow of the dynamics are computed using a low-fidelity dynamical model to maximize computational efficiency and corrected with selected high-fidelity samples to minimize accuracy losses. The effectiveness of the proposed method is demonstrated for different dynamical regimes combining SGP4 theory and numerical propagation as low- and high-fidelity models respectively., Comment: 24 pages, 5 figures

Here, a canonical model is proposed, which is able to represent the flow past a wing equipped with a pylon-mounted engine at low speed/moderate angle of attack. The vortices that develop past this model are described numerically and experimentally. For such configurations, the presence of a power-plant installation under the wing initiates a complex and unsteady vortical flowfield at the nacelle/pylon/wing junctions, responsible for a drop in aircraft performances. To gain insight into the underlying physics, the geometry is simplified into a symmetric two-dimensional extruded wing equipped with a symmetric, hemispheric-ended cylinder. The study was conducted at a Reynolds number of 200,000, based on the wing chord and on the freestream velocity. Two angle of attack α=sideslip angle β configurations are investigated on the basis of unsteady Reynolds-averaged Navier–Stokes computations, oil-flow visualizations, and stereoscopic particle image velocimetry. The vortex dynamics thus produced is described in terms of vortex core position, intensity, and size. The analysis of the velocity flowfields obtained from the wind-tunnel measurements and the numerical computations highlights the influence of the longitudinal vortex initiated at the pylon/wing junction on the separation process of the boundary layer near the upper-wing leading edge.

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This paper aims to perform a drag breakdown of an airfoil and a wing by using the exergetic method. Moreover, a new far-field wave anergy extraction method is presented. The resulting exergetic drag curves are proposed as additional characteristic curves for external aerodynamic assessment of airfoils or any other bodies. CFD analyses of a NACA 0012 airfoil and a rectangular wing at subsonic and transonic conditions were used as test cases to present the concept. This new approach allows to deeply understand the aerodynamic behavior of a body and provides an alternative point of view to the classical near-field and far-field based drag curves.

In this Note, the origin of the oscillation modes of screeching round jets is investigated by assuming that the feedback part of the aeroacoustic loop responsible for screech noise can be modeled by considering the neutral acoustic wave modes of the equivalent ideally expanded jets.

In this paper, we document the capabilities of a novel numerical approach - the immersed boundary lattice Green's function (IBLGF) method - to simulate external incompressible flows over complex geometries. This new approach is built upon the immersed boundary method and lattice Green's functions to solve the incompressible Navier-Stokes equations. We show that the combination of these two concepts allows the construction of an efficient and robust numerical framework for the direct numerical and large-eddy simulation of external aerodynamic problems at moderate to high-Reynolds numbers.

Flow structure oscillations and tone generation mechanisms in an underexpanded round jet impinging on a flat plate normally have been investigated using compressible large-eddy simulations. At the exit of a pipe nozzle of diameter D, the jet is characterized by a nozzle pressure ratio of 4.03, an exit Mach number of 1, a fully expanded Mach number of 1.56, and a Reynolds number of 60000. Four distances between the nozzle and the plate are considered. Snapshots of vorticity, density, pressure, and mean velocity flowfields are first presented. The latter results compare well with data of the literature. In three cases, in particular, a Mach disk appears to form just upstream from the plate. The convection velocity of flow structures between the nozzle and the plate, and its dependence on the nozzle-to-plate distance, are then examined. The properties of the jet near pressure fields are subsequently described using Fourier analysis. Tones emerge in the spectra at frequencies consistent with those expected for an aeroacoustic feedback loop between the nozzle and the plate as well as with measurements. Their amplitudes are particularly high in the presence of a near-wall Mach disk. The axisymmetric or helical natures of the jet oscillations at the tone frequencies are determined. The motions of the Mach disk found just upstream from the plate for certain nozzle-to-plate distances are then explored. As noted for the jet oscillations, axially pulsing and helical motions are observed, in agreement with experiments. Finally, the intermittency of the tone intensities is studied. They significantly vary in time, except for the two cases where the near-wall Mach disk has a nearly periodic motion at the dominant tone frequency.

The trailing edge noise, or the so-called self-noise of an airfoil, significantly contributes to the broadband noise in various configurations such as high bypass-ratio engines and counter-rotating open rotors. The present work aims at characterizing the wall-pressure fluctuations in the turbulent boundary layer just upstream the trailing edge, that are known to shape the trailing edge noise spectrum. These investigations are carried out using large- eddy simulations, with the massively parallel compressible solver CharLESX, of the flow over a truncated NACA0012 airfoil at Rec = 4×105 for angles of attack α = 0◦ and α = 6.25◦. Unsteady wall-pressure signals are recorded using several thousands of probes distributed over the suction side. We focus on data-processing the pressure signals to extract quantities crucial to trailing edge noise modelling: the convection velocity Uc, the spanwise correlation length lz and the spectrum of the wall-pressure fluctuations Φpp.

The French Ministry of Defence’s procurement agency, the Direction Generale de l'Armement (DGA), is in charge of assessing and testing armament systems in order to equip the armed forces and prepare for the future. DGA Aeronautical Systems, the technical centre dedicated to evaluating and testing aircraft, combines tests and evaluations to clear,among other things, parachute systems inside the Airdrop Department. In order to have a greater understanding of the behavior of parachute dynamics and to optimize the parachute system’s flight tests, DGA Aeronautical Systems developed a modelling and simulation capability as an evaluation tool. Also, under the tutelage of the French Ministry of Defence,the Department of Aerodynamics, Energetics and Propulsion (DAEP) within the Institut Superieur de l’Aeronautique et de l’Espace (ISAE) - a public institution of higher education and research - conducts research and training support for the Institute. As such, it has developed over the past ten years the topic of study "Aerodynamics of Free Flight Devices" focused particularly on paragliding. The work in this framework has allowed the formation of a basis of experimental data and the development of models to improve the design and the safety of parachutes and paragliders. Moreover, the ISAE/DAEP has expertise and resources in the field of wind tunnel tests and the study of aerodynamics and flight mechanics for paragliders. These two entities of the French Ministry of Defence work in cooperation since two years on the identification of aerodynamic coefficients for ram air parachutes. Indeed, ram-air flight dynamics are poorly understood in regard to the requirement to provide input data to a new model for an unmanned parafoil fitted with payloads. It’s necessary to better understand the methods to evaluate and measure flight dynamic coefficients to improve the control guidance of operational ram-air parachutes. To avoid wasting time, and carrying out numerous expensive test flights to obtain a limited amount of experimental data, these two entities have decided to share their skills with the aim of obtaining a ram-air parachute numerical model. For this purpose, since 2003, DGA Aeronautical Systems have developed Fluid Structure Interaction (FSI) simulations of parachutes using the LS-Dyna® commercial Finite Element Analysis (FEA) tool. This tool is largely used for solving highly non-linear transient problems and enables the coupling of multi-physics simulations such as FSI simulations. This paper presents the latest improvements to the FSI simulation of ram-air parachutes, applied to a kite. This first step is necessary in order to work at low complexity before going on to more intricate applications. After explaining our experimental methodology for validation using wind tunnel tests, the method to modelize the whole kite is detailed. The comparison of relevant criteria between the experiment and the simulation results demonstrate a good accordance.

Hypotheses adopted for conventional ram-air gliding parachutes are not valid for paraglider aerodynamics and they require a new investigation. This paper presents an experimental database for a reference wing representative of a paraglider wing. Interest is focused on the external flow and on the influence of the spanwise arched shape on stationary longitudinal and lateral aerodynamic characteristics.To isolate this effect, leading edge intake and swell of real textile inflated cells are not represented. Thus,the reference wing is rigid and filled.

This paper proposes a double input output port transfer to model complex mechanical systems composed of several sub-systems. The sub-structure decomposition is revisited from the control designer point of view. The objective is to develop modelling tools to be used for mechanical/control co-design of large space flexible structures involving various substructures (boom, links of robotic arm,...) connected one to each other through dynamics local (actuated) mechanisms inducing complex boundary conditions. The double input output port model of each substructure is a transfer where accelerations and external forces at the connection points are both on the model inputs and outputs. Such a model : * allows to the boundary conditions linked to interactions with the other substructures to be externalized outside the model, * is defined by the only substructure own dynamic parameters, * allows to build the dynamic model of the whole structure by just assembling the double port models of each substructure. The principle is first introduced on a single axis spring-mass system and then extented to the 6 degress-of-freedom case. This generalization uses the clamped-free substructure dynamic parameters such as finite element softwares can provide.

The present paper investigates a time-domain harmonic balance method as an alternative to classical time-marching schemes for stability studies of turbomachineries toward flutter. A weak-coupling approach is applied, which requires computing the fluid response to prescribed harmonic motions of the structure. The harmonic balance method, formulated in the arbitrary Lagrangian/Eulerian framework, is adapted to single-passage reduction using phase-lag boundary conditions expressed purely in the time domain. Validation against experimental data for the 11th standard configuration for aeroelasticity is performed, showing good agreement. Finally, an industrial test case is presented: a fan designed by Safran Snecma. The results show the good accuracy of the proposed harmonic balance method as well as significant reductions in computational time.

This paper presents an experimental test bed developed in the DMIA lab of ISAE. The main interest is to study human factors in aircraft control and guidance and the usage of active feedback devices to provide kinesthesic sensations to pilots. The experimental set-up comprises a complete simulation environment composed of a custom-made flight mechanics model and visuals engine, together with a one-degree-of-freedom active yoke device. The aim of the project is to adapt the yoke impedance to specific flight condition and in this particular case the guidance assistance. In the final paper tests will be performed using a set of at minimum ten subjects to demonstrate the interest of this haptic aiding.

In this paper, the modeling of flexible multi-body systems (typically a satellite), the design of a reduced-order robust controller and the closed-loop system robustness analysis are considered. First, we present a generic tool developed to build the model of a multi- body dynamic system taking into account parametric uncertainties for robust control and analysis purpose. Satellites are typically composed of a main body (hub of the satellite) and cantilevered appendages (flexible or not). Based on the description of each element(mechanical and geometrical properties, uncertain parameters ...), a linear model between torques applied to the hub (control or perturbation inputs) and angular accelerations is built using the Linear Fractional Representation framework. Second, based on this model, a control design method is proposed: from a basic standard scheme and the latest H_infinity solver, a low order H1 controller can be derived. Roll-off requirements and worst-case parametric configurations can also be taken into account in a multi-model design approach. Third, robustness analysis of the design on the full order model is considered. A numerical example illustrate the relevance and effectiveness of the proposed approach.

This paper presents a detailed study of a flapped outflow valve. Well-known as part of the pressurization system of aircraft, this type of valve is also designed for thrust recovery even if the efficiency of the system has never been demonstrated. Aground experimental test rig is first designed to provide global and local measurements to be used as validation data for numerical simulations. Once the validation of the numerical approach is achieved on a ground configuration, additional three-dimensional computations are then conducted for cruise conditions. They lead to a reliable estimation of thrust recovery as well as interesting insight in the aerodynamic behavior of the flow across the valve and its associated three-dimensional effects.

The resilience of a system consists in its capability to maintain a safe and satisfactory mission, in its operational environment, while adapting to changing conditions (foreseen or unforeseen events, losses, failures,...) and mitigating the risk of contingencies. To guarantee the success of the ATV future missions (from ATV2, Johannes Kepler), the operational teams at ATV-CC(ATV Control Center), with the help of the vehicle designers, have built dedicated processes, developed particular tools and set specific advanced training right from the earliest preparation phase. In order to be compliant with strong safety requirements (due to the proximity of and interfaces with the ISS), operational teams have to prepare strategies balancing total automation versus human reaction, or training (at least, one procedure for each foreseen case) versus adaptation. Combining system engineering principles and lesson learnt from ATV Jules Verne mission, the Vehicle Team (VET) at ATV-CC challenges the improvement of the global system resilience through several means (ground and on-board alarms, specialized procedures, specific displays,...) depending on contingencies level, for next missions. The paper describes the strategies (in term of processes and tools) set up by the Vehicle Engineers Team, in accordance to safety requirements, interfaces with the international partners and ATV-CC rules to ensure the ATV operations.

This paper addresses one of the key components required to produce an environmentally friendly aircraft by reducing drag (and hence fuel consumption) through improved aerodynamic integration of the wing, pylon, and nacelle. The results of a computational investigation comparing the aerodynamic performance of a compression pylon design to a DLR F6 based conventional pylon design are presented in this paper. As with other computational predictions, the total lift and total drag were overpredicted. The change in drag between the wing body and the wing-body nacelle-pylon configurations was underpredicted by 14% at CL = 0.5. This validated CFD method was then used to investigate a compression pylon design. The results showed that a compression pylon produces an increase in lift and a reduction in drag. At zero degree angle of attack the total drag coefficient was reduced by at least 0.0006. The effect of the pylon is primarily inboard of the wing.

In this paper, the optimization of interacting lift ing surfaces based on design of experiments (DoE) and response surface technique (RSA) is investigated. Response surfaces of the considered problem are generated through the use of high-fidelity two-dimensional Reynolds Average Navier-Stokes simulations. The large number of simulations necessary to populate response surfaces is obtained by using a n ewly developed automated simulation platform named ADONF  . This platform integrate a RANS, URANS flow solver with an automated CAD and mesh generation algorithm and a panel of optimization tools which may be used to generate approximate response surfaces through design of experiments. To gain knowledge about the potential of these tools t o resolve non linear fluid flow optimization problems, we have used this simulation environment to study a sailing yacht problem. The aerodynamic performance optimization of complex rigs composed by multiple interacting masts and sails has been investigated. This problem is a well known by sailors because of its crucial importance for high speed sa iling yachts and has been a subject of debate and controversy since many years. A new look on this problem is proposed through viscous CFD with parametric and topological optimization. It is a preliminary twodimensional study with a moderate design space size which will be extended to three dimensional problems and a larger design space size.

In this paper, we propose a Lagrange-Kuhn-Tucker based coordination scheme to deal with level coupling. First, we give a precise definition of several multilevel decomposition schemes, namely the StiffOpt -industrial- approach, and the minMass approach which keeps a mass minimization as objective of local optimisations. Then, we introduce a new decomposition strategy using dual variables. Last section is dedicated to numerical results and comparison of these approaches on the classical ten bar truss problem benchmark.

An experimental investigation of the effects of humidity-induced condensation on shock/boundary-layer interaction has been conducted in a transonic wind-tunnel test. The test geometry considered was a wall-mounted bump model inserted in the test section of the wind tunnel. The formation of a lambda-shape condensation shock wave was shown from schlieren visualization and resulted in a forward movement of the shock wave, reduced shock wave strength, and reduced separation. Empirical correlations of the shock wave strength and humidity/dew point temperature were established. For humidity levels below 0.15 or a dew point temperature of 268 K, the effect of humidity was negligible. The unsteady pressure measurements showed that if a condensation shock wave formed and interacted with a main shock wave, the flow becomes unsteady with periodic flow oscillations occurring at 720 Hz.