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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.

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.

Increasing the wing aspect ratio appears as a straightforward way to improve aerodynamic performance of transport aircraft by reducing the lift-induced drag component. However, it comes at the price of a direct negative impact on the wing structural weight which is necessary to sustain aerodynamic loads in the case of a conventional cantilever wing. The strut-braced wing concept allows to reduce the flexural moment to be carried out by the inner-wing structure and therefore limits the weight penalty as aspect ratio is increased. A multidisciplinary evaluation of the potential benefits at aircraft level of High Aspect Ratio, Strut Braced Wing concept is presented. It relies on a multi-fidelity design approach in which an Overall Aircraft Conceptual Design framework is combined with high-fidelity aerodynamic and structural analyses to provide accurate physical information to the conceptual design process. This paper describes the tools, framework and approach used to combine OACD with high-fidelity CFD and CSM analyses and illustrates the first results of its application to design a HAR-SBW aircraft concept which are compared to a conventional tube-and-wing aircraft designed for the same mission., Réduire l'empreinte environnementale de l'aviation et surtout son impact sur le changement climatique est aujourd'hui devenu l'enjeu majeur de l'industrie aéronautique. Dans ce contexte, la Commission européenne s'est fixé des objectifs ambitieux pour l'aviation définis dans le « Fligthpath 2050 », notamment une réduction de 75 % des émissions de CO2 et de 90 % des émissions de NOx, ainsi qu'une réduction de 65 % du bruit. Atteindre de tels objectifs ne sera probablement possible que grâce à des évolutions radicales de l'architecture de l'avion, du système de propulsion et de l'introduction de technologies de rupture. Pour ce qui concerne l'architecture de l'avion, le Blended Wing Body (BWB) et le Strut-Braced Wing (SBW) semblent aujourd'hui être les deux alternatives les plus prometteuses à la configuration classique "Twin Underwing Turbofan Tube-and-Wing" qui est devenue prédominante. solution au cours des dernières décennies. Le BWB et le Hybrid Wing Body sont actuellement étudiés dans le cadre de plusieurs efforts de recherche importants en Europe, aux États-Unis et en Chine. Le présent article présente des enquêtes sur la configuration SBW. La principale justification de la configuration SBW est de permettre une augmentation significative du rapport d'aspect de l'aile (AR) pour améliorer les performances globales de l'avion grâce à des gains d'efficacité aérodynamique sans l'énorme augmentation du poids de l'aile dont souffrirait une aile en porte-à-faux d'un AR similaire. Ceci est obtenu grâce à une réduction du moment de flexion dans le caisson de voilure interne permise par une traction de la jambe de force à sa jonction avec l'aile. Cela permet de réduire la taille des composants structurels du caisson de voilure dans l'aile intérieure qui sont principalement dimensionnés par le moment de flexion dans le cas d'une aile en porte-à-faux.Ce concept peut être utilisé pour augmenter l'allongement de l'aile et profiter d'une réduction de la traînée aérodynamique (en réduisant réellement la traînée induite par la portance) tout en contenant l'augmentation du poids structurel de l'aile associée à une envergure plus élevée (impliquant un moment de flexion plus élevé dans l'aile centrale -boîte). Par conséquent, l'ajout d'une jambe de force, ou plus généralement d'une structure en treillis, ouvre un degré de liberté supplémentaire pour le concepteur afin de mieux exploiter les ailes à rapport d'aspect élevé au niveau global de l'avion en réalisant un nouveau compromis optimal (par rapport au cantilever, sans jambe de force, aile) entre l'efficacité aérodynamique et le poids de l'aile.De tels compromis pour le concept d’aile haubanée ont déjà été étudiés à l'ONERA dans le projet ALBATROS. Plus récemment, dans le projet de thèmes thématiques Clean-Sky 2 U-HARWARD (www.u-harward-project.eu/), différentes solutions au niveau de l'avion permettant d'augmenter l'allongement des ailes sont étudiées pour réduire l'impact environnemental et améliorer les performances. Dans ce projet, l'ONERA et l'ISAE explorent les avantages potentiels et les éventuels pièges du concept SBW à travers une approche de conception multi-niveaux multidisciplinaire comprenant la conception globale de l'avion (OAD) et des études de conception disciplinaires affinées de l'aérodynamique et des aspects structurels clés du concept d’aile haubanée.L'article final présentera les modèles et outils mis en place pour effectuer l'exploration de conception multidisciplinaire à plusieurs niveaux du concept SBW au sein du projet U-HARWARD, ainsi que la conception intermédiaire obtenue.

In 2019, aviation was responsible for 2.6% of the world CO2 emissions as well as additional climate impacts such as contrails. Like all industrial sectors, the aviation sector must implement measures to reduce its climate impact. This paper focuses on the simulation and the evaluation of climatic scenarios for the aviation industry. For this purpose, a specific tool (CAST for "Climate and Aviation - Sustainable Trajectories") has been developed. This tool follows a methodology adapted to aviation using the concept of carbon budget and models of the main levers of action such as the level of air traffic, reduction of aircraft energy consumption or energy decarbonisation. These models are based on trend projections from historical data or assumptions from the literature. Several scenario analyses are performed in this paper using CAST and allow several conclusions to be drawn. For instance, the modelling of the scenarios based on the ATAG (Air Transport Action Group) commitments shows that aviation would consume between 2.9% and 3.5% of the world carbon budget to limit global warming to 2{\deg}C and between 6.5% and 8.1% for 1.5{\deg}C. Also, some illustrative scenarios are proposed. By allocating 2.6% of the carbon budget to aviation, it is shown that air transport is compatible with a +2{\deg}C trajectory when the annual growth rate of air traffic varies between -1.8% and +2.6%, depending on the considered technological improvements. However, in the case of a +1.5{\deg}C trajectory, the growth rate would have to be reduced drastically. Finally, analyses including non-CO2 effects compel to emphasize the implementation of specific strategies for mitigating contrails., Comment: 41 pages, 14 figures, 4 tables, Research paper

International audience; The present investigation addresses two key issues in aerodynamic performance of a propeller–wing configuration, namely linear and nonlinear predictions with low-order numerical models. The developed aerodynamic model is targeted to be used in the preliminary aircraft design loop. First, the combination of selected propeller model, i.e. blade element theory with the wing model, i.e. lifting line theory and vortex lattice method is considered for linear aerodynamic model. Second, for the nonlinear prediction, a modified vortex lattice method is paired with the two-dimensional viscous effect of the airfoils to simplify and reduce the computational time. These models are implemented and validated with existing experimental data to predict the differences in lift and drag distribution. Overall, the predicted results show agreement with low percentage of error compared with the experimental data for various thrust coefficients and produced induced drag distribution that behaves as expected.

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.

This paper presents the development of a code, called GEBTAero, dedicated to very flexible aircraft (VFA) aeroelasticity and especially the evaluation of aeroelastic tailoring effect on critical speeds. GEBTAero is an open source code consisting in a tightly coupling between a geometrically exact beam theory -and a finite state induced flow unsteady aerodynamic model, including an homogenisation tool. This model has been implemented in Fortran using GEBT code and optimised open source libraries with particular focus on computation speed. Besides a non linear transient dynamic simulation capacity, a particular focus is put on the fast critical speed computation strategy using a non-iterative modal approach about the geometrically non linear deformed shape of the wing with the computation of only a few aeroelastic modes. Computation speed and accuracy of this implementation is assessed using widely used aeroelastic test cases and compared successfully to other aeroelastic codes. Configurations using aeroelastic tailoring, which are the core target of this solver, are then evaluated numerically on a representative high aspect ratio anisotropic composite wing and a simple 2-ply composite laminates with both variable ply orientations. It illustrates the strong correlation between the structural bending/twisting coupling of an unbalanced composite laminates and its critical aeroelastic speed. It also shows the high sensitivity of ply orientation on the aeroelastic behaviour.

With the increase in the air traffic, reducing the aviation environmental impact is the key challenge of the community. This has called for more research in the area of using alternative fuels which will reduce the greenhouse gas emissions and which can provide similar or better environmental performance. This work presents a preliminary design methodology of a mid-range single aisle commercial aircraft using Hydrogen as fuel which is stored in an integrated tank in the fuselage. The iterative design process was achieved by using overall aircraft design approach through the FAST-OAD open-source software. This study describes the models used for a first approximation of structural and insulation weight of liquid Hydrogen (LH2) tank and fuel boil off computations. It then presents the impacts of an LH2 storage system on the overall aircraft design with an emphasis on the centre of gravity (CG) travel and the additional fuselage length necessary to accommodate the LH2 tank. An additional parametric study has also been carried out to understand the effect of some design parameters on overall design. Finally, an environmental study has been conducted to evaluate the direct emissions of this aircraft in operation. The only emissions that result from the combustion of hydrogen are nitrogen oxides (NOx) which were evaluated using the Boeing Fuel Flow Method (BFFM2) and water vapor (H2O) which was evaluated based on the fuel burned. As a result of this study significant reduction in NOx and CO2 emissions as compared to existing design are envisaged, thus showing the promising potential of Hydrogen fuelled aircraft.

Distributed electric propulsion is a fertile research topic aiming to increase the wing aerodynamic efficiency by distributing the thrust over the wing span. The blowing due to distributed propulsors shall increase the wing lift coefficient for a given planform area and flight speed. This should bring several advantages as wing area, drag, and structural weight reduction, which in turn reduce fuel consumption, allowing airplanes to fly more efficiently. However, there are no consolidated preliminary design methods to size a distributed propulsion system. Numerical analysis is then performed at early stage, where many design variables have not been fixed yet. Therefore, the design space is vast and exploring all the possible combinations is unfeasible. For instance, low-fidelity methods (VLM, panel codes) have a low computational time, but usually they do not account for flow separation and hence they are unable to predict the wing maximum lift. Conversely, high-fidelity codes (CFD) provide more realistic results, but a single drag polar sweep can last days. This work provides a benchmark of different aerodynamic solvers for a typical regional turboprop wing with flaps and distributed propulsion, to better understand the limits of each software in the prediction of aero-propulsive effects.

International audience; Fixed-wing miniature aerial vehicles usually fly at low altitudes that are often exposed to turbulent environments. Gust soaring is a flight technique of energy harvesting in such a complex and stochastic domain. The presented work shows the feasibility and benefits of exploiting a nonstationary environment for a small unmanned aerial vehicle. A longitudinal dynamics trajectory is derived, showing significant benefits in extended flight with a sinusoidal wind profile. An optimization strategy for active control is performed, with the aim of obtaining the most effective set of gains for energy retrieval. Moreover, a three-dimensional multipoint model confirms the feasibility of energy harvesting in a more complex spatial wind field. The influence of unsteady aerodynamics is determined on the overall energy gain along the flight path with active proportional control. The aerodynamic derivatives describing the contribution to lift by a change in angle of attack and elevator deflection are identified as the most contributing aerodynamic parameters for energy harvesting in a gusty environment, and are therefore suggested as a basic objective function of an unmanned aerial vehicle design for such a flight strategy.

In 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.

International audience

International audience; Fixed-wing small, unmanned aerial vehicles (SUAVs) usually fly in atmospheric boundary layers that are often under the influence of turbulent environments. Inspired by nature's flyers, an application of an energy-harvesting flight strategy for increasing the energy state of the aircraft is presented. This paper provides basic longitudinal flight dynamic model exposing the physics behind the process. It shows significant power savings in flight with a sinusoidal and stochastic wind profile with active control of energy-harvesting. The active control based on optimized proportional gains was implemented for energy extraction from realistic atmospheric conditions, leading to significant energy savings for a 'bird-sized' vehicle. The paper reveals the equipment and necessary preparations for the flight test campaign. Moreover, it describes the design of a custom controller and its calibration in the wind tunnel against roll movements during pitching maneuvers. Finally, it investigates the benefits and potential of the automated process of energy-harvesting with simple proportional control through flight tests in a turbulent environment, validating the concept through the increased energy state of the aircraft.

Nowadays, digitalisation of aircraft, of their operations and their support became a crucial component for all the market players of the aeronautical industry. This technical field occupies an increasingly significant place, due to the generation of a substantial volume and an extensive variety of operational data. This new trend suggests taking those data into account during preliminary design and certification steps, in order to include additional considerations during those phases, such as operational criteria, maintenance, added value, development times or certification delays. In that way, this paper aims at suggesting a methodology to consolidate the aircraft design and certification processes though the use of those novel “digital” resources.

To face the increasing environmental footprint of commercial aviation, industrial and research efforts have been focusing on exploring unconventional configurations and new propulsion paradigms, mostly based on electric technology. Such explorations require Overall Aircraft Design that has to be performed in an integrated multidisciplinary design environment. Such design environments are often limited to multidisciplinary analysis, adapted for a single aircraft configuration or require an important effort to be mastered. FAST-OAD is a software program developed by ONERA and ISAE-SUPAERO for aircraft sizing analysis and optimization that aims at user friendliness and modularity. It is an aircraft sizing code based on multidisciplinary design optimization techniques and the point mass approach to estimate the required fuel and energy consumption for a given set of TLARs. This paper presents the motivations for moving from the original software program, called FAST, to the open source code FAST-OAD based on OpenMDAO.

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 order to reduce the CO2 emissions, a disruptive concept in aircraft propulsion has to be considered. As studied in the past years hybrid distributed electric propulsion is a promising option. In this work the feasibility of a new concept aircraft, using this technol- ogy, has been studied. Two different energy sources have been used: fuel based engines and batteries. The latters have been chosen because of their flexibility during operations and their promising improvements over next years. The technological horizon considered in this study is the 2035: thus some critical hypotheses have been made for electrical compo- nents, airframe and propulsion. Due to the uncertainty associated to these data, sensivity analyses have been performed in order to assess the impact of technologies variations. To evaluate the advantages of the proposed concept, a comparison with a conventional aircraft (EIS 2035), based on evolutions of today’s technology (airframe, propulsion, aerodynamics) has been made.

International audience; The aviation's goal for the next decades is to drastically reduce emissions, but to achieve this goal a breakdown in aircraft design have to be considered. One of the most promising concept is the Blended Wing-Body, which integrates aerodynamics, propulsion and structure, and has a better aerodynamics efficiency, thanks to the reduction of the wetted surfaces. In this work the feasibility of a short/medium range BWB with 150 passengers (A320 type aircraft, Entry Into Service 2035) is studied, considering different disciplines into the sizing process. To supply the lack of reference data, an approach that goes from high fidelity to validate low fidelity models has been set up. Also certification aspects have been taken into account in an off-design analysis. To evaluate the advantages of the proposed concept, it has been compared with an aircraft of the same class, the A320 Neo, resized to match the EIS2035 hypothesis: results show that the BWB is a concept that shows a gain in fuel consumption, especially on longer ranges.

International audience; Fixed-wing mini aerial vehicles usually at low altitudes often exposed to turbulent environments. Gust soaring is a flight technique of energy harvesting in such a complex and stochastic domain. Presented work shows the feasibility and benefits of exploiting non-stationary environment for a small UAV. Longitudinal dynamics trajectory is derived showing significant benefits in extended flight with sinusoidal wind profile. Optimization strategy for active control has been performed with the aim of obtaining most effective set of gains for energy retrieval. Moreover, three-dimensional multi-point model confirmed feasibility of energy harvesting in a more complex spatial wind field. Influence of unsteady aerodynamics is determined on overall energy gain along the flight path with active proportional control. Most contributing aerodynamic parameters are identified and suggested as basic objective function of an UAV design for energy harvesting in gusty environment. In addition, passive approach of control related to structural dynamics is investigated, pointing out its potential and possible improvements with aeroelastic tailoring.

In 1996, a trinucleotide circular code which is maximum, self-complementary, and , called , was identified statistically on a large gene population of eukaryotes and prokaryotes (Arquès and Michel (1996)). Transition and transversions I and II are classical molecular evolution processes. A comprehensive computer analysis of these three evolution processes in the code shows some new results; in particular (i) transversion I on the 2nd position of any subset of trinucleotides of generates trinucleotide circular codes which are always and (ii) transversion II on the three positions of any subset of trinucleotides of yields no trinucleotide circular codes. These new results extend our theory of circular code in genes to its evolution under transition and transversion.

International audience; A full spatio-temporal four-dimensional characterization of the microphysics and dynamics of cloud formation including the onset of precipitation has never been reached. Such a characterization would yield a better understanding of clouds, e.g. to assess the dominant mixing mechanism and the main source of cloudy updraft dilution. It is the sampling strategy that matters: fully characterizing the evolution over time of the various parameters (P, T, 3D wind, liquid water content, aerosols...) within a cloud volume requires dense spatial sampling for durations of the order of one hour. A fleet of autonomous lightweight UAVs that coordinate themselves in real-time as an intelligent network can fulfill this purpose. The SkyScanner project targets the development of a fleet of autonomous UAVs to adaptively sample cumuli, so as to provide relevant data to address long standing questions in atmospheric science. It mixes basic researches and experimental developments, and gathers scientists in UAV conception, in optimal flight control, in intelligent cooperative behaviors, and of course atmospheric scientists. Two directions of researches are explored: optimal UAV conception and control, and optimal control of a fleet of UAVs. The design of UAVs for atmospheric science involves the satisfaction of trade-offs between payload, endurance, ease of deployment... A rational conception scheme that integrates the constraints to optimize a series of criteria, in particular energy consumption, would yield the definition of efficient UAVs. This requires a fine modeling of each involved sub-system and phenomenon, from the motor/propeller efficiency to the aerodynamics at small scale, including the flight control algorithms. The definition of mission profiles is also essential, considering the aerodynamics of clouds, to allow energy harvesting schemes that exploit thermals or gusts. The conception also integrates specific sensors, in particular wind sensor, for which classic technologies are challenged at the low speeds of lightweight UAVs. The overall control of the fleet so as to gather series of synchronized data in the cloud volume is a poorly informed and highly constrained adaptive sampling problem, in which the UAV motions must be defined to maximize the amount of gathered information and the mission duration. The overall approach casts the problem in a hierarchy of two modeling and decision stages. A macroscopic parametrized model of the cloud is built from the gathered data and exploited at the higher level by an operator, who sets information gathering goals. A subset of the UAV fleet is allocated to each goal, considering the current fleet state. These high level goals are handled by the lower level, which autonomously optimizes the selected UAVs trajectories using an on-line updated dense model of the variables of interest. Building the models involves Gaussian processes techniques (kriging) to fuse the gathered data with a generic cumulus conceptual model, the latter being defined from thorough statistics on realistic MesoNH cloud simulations. The model is exploited by a planner to generate trajectories that minimize the uncertainty in the map, while steering the vehicles within the air flows to save energy.

International audience; A passive twist control is considered as an adaptive way to maximize the overall efficiency of a proprotor developed for convertible Micro Air Vehicles (MAV). In this paper, adaptation of the proprotor geometry in accordance to flight configurations is achieved by induced twist generated by the inherent structural coupling effect in anisotropic composite material and centrifugal force emanating from the tip load. Beam Finite Element Model based on Rotating Timoshenko Theory is used to predict structural loads, while Blade Element Momentum Theory is employed to predict the aerodynamic performance of adaptive proprotor as applied on Micro Air Vehicles (MAV). The iterative process of combination of aerodynamic model and structural model is used to compute the steady-state deformation of the flexible laminated proprotor blade due aerodynamic loads. Finally, the optimal design of lamina blade material is carried out to investigate the potential of flexible blade in the proprotorperformance enhancement.

Dynamic soaring is a flying technique which extracts energy from an environment where wind gradients form, such as the air-sea interface above oceans that sees such gradients developing through multiple and combined phenomena. Models of wind-wave interactions are analysed in terms of their influence on the induced wind field, before selecting a purely sinusoidal peak wave from the wave spectrum and developing the related wind field using stable laminar theory. Dynamic soaring trajectories are then derived by optimising a nonlinear constrained problem that models the evolution of a point mass vehicle. Characteristic phases of dynamic soaring flight are evidenced out of the overall trajectories and compared to the flat-ocean case in order to conclude on the influence of waves regarding dynamic soaring performances.

Pressure-loss data are reported for three-phase oil–water–gas flow in horizontal pipes of 0.0259 and 0.0501 m i.d. The pressure profiles exhibited a maximum value above a critical gas rate, which progressively moved to higher oil ratios as the gas rate was increased due to increased turbulence within the system. The actual pressure-drop profiles obtained depended mainly on the flow regimes present within the system. As the pipe diameter was reduced, the pressure drop was observed to increase for the same flow conditions. Above a critical gas rate the magnitude of the pressure drop was higher if approached for the oil-dominated (OD) region compared to the opposite direction. A momentum-balance model was proposed for prediction of the pressure drop, which gave improved performance over other existing methods. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

Pressure drop measurement and prediction in curved pipes and elbow bends is reviewed for both laminar and turbulent single-phase fluid flow. For curved pipe under laminar flow, the pressure loss can be predicted both theoretically and using empirical relations. The transitional Reynolds number can be predicted from an empirical relation. Turbulent flow in curved pipes can only be theoretically predicted for large bends but there are a large number of empirical relations that have proved to be accurate. Elbow bends have proven to be difficult to both measure and represent the pressure loss. Methods of overcoming such problems are outlined. There was no reliable method of theoretically predicting pressure drop in elbow bends. Experimental measurements showed considerable scatter unless care was taken to eliminate extraneous effects. Reliable data are highlighted and an empirical method is proposed for calculation of pressure drop in elbow bends.

Prediction of two-phase pressure drop using published correlations and a wide data base showed that no single correlation could predict across the whole range of possible flow patterns. Particular difficulty was found in attempting to predict the intermittent SI and BTS patterns. However, successful prediction was achieved for the St + RW, St + RW + D, D and A + RW patterns. Two-phase pressure drop predictive correlations were extended to the three-phase situation. Detailed evaluation identified three correlations which gave reasonable prediction of intermittent flow pressure drop. An adaptation is presented that enhances the prediction of these correlations for three-phase flow. The separated three-phase patterns could not be predicted to an acceptable standard using these types of correlations.

A methodology to estimate the cost implications of design decisions by integrating cost as a design parameter at an early design stage is presented. The model is developed on a hierarchical basis, the manufacturing cost of aircraft fuselage panels being analysed in this paper. The manufacturing cost modelling is original and relies on a genetic-causal method where the drivers of each element of cost are identified relative to the process capability. The cost model is then extended to life cycle costing by computing the Direct Operating Cost as a function of acquisition cost and fuel burn, and coupled with a semi-empirical numerical analysis using Engineering Sciences Data Unit reference data to model the structural integrity of the fuselage shell with regard to material failure and various modes of buckling. The main finding of the paper is that the traditional minimum weight condition is a dated and sub-optimal approach to airframe structural design.

Pressure drop data are reported for two phase air–water flow through a vertical to horizontal 90° elbow bend set in 0.026 m i.d. pipe. The pressure drop in the vertical inlet tangent showed some significant differences to that found for straight vertical pipe. This was caused by the elbow bend partially choking the inflow resulting in a build-up of pressure and liquid in the vertical inlet riser and differences in the structure of the flow regimes when compared to the straight vertical pipe. The horizontal outlet tangent by contrast gave data in general agreement with literature even to exhibiting a drag reduction region at low liquid rates and gas velocities between 1 and 2 m s−1. The elbow bend pressure drop was best correlated in terms of le/d determined using the actual pressure loss in the inlet vertical riser. The data showed a general increase with fluid rates that tapered off at high fluid rates and exhibited a negative pressure region at low rates. The latter was attributed to the flow being smoothly accommodated by the bend when it passed from slug flow in the riser to smooth stratified flow in the outlet tangent. A general correlation was presented for the elbow bend pressure drop in terms of total Reynolds numbers. A modified Lockhart–Martinelli model gave prediction of the data.

Holdup data are presented for three-phase co-current oil-water-air in a horizontal 0.0259 m i.d. pipe. Detailed two-phase studies confirmed the validity of the experimental technique employed. A model is presented for the prediction of oil-air two-phase holdup. The three-phase holdup values were shown to be flow regime dependent and could be qualitatively explained on the basis of the fine structure of the liquid phases. A model is presented for the prediction of three-phase liquid holdup. This work extends the regime study by Spedding et al. (Trans. Inst. Chem. Eng, Part A, Chem. Eng. Res. Des. 2005, 83A: 401–411) to holdup measurement and prediction for three-phase flow. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

International audience; A passive twist control is proposed as an adaptive way to maximize the overall efficiency of the small-scale rotor blade for multifunctional aircrafts. Incorporated into a database of airfoil characteristics, Blade Element Momentum Theory is implemented to obtain the blade optimum twist rates for hover and forward flight. In order to realize the required torsion of blade between hover and forward flight, glass/epoxy laminate blade is proposed based on Centrifugal Force Induced Twist concept. Tip mass is used to improve the nose-down torsion and the stabilization of rotating flexible blade. The laminate blades are tested in hover and forward flight modes, with deformations measured by Laser Displacement Sensor. Two Laser Displacement Sensors are driven by the tracking systems to scan the rotating blade from root to tip. The distance from blade surface to a reference plane can be recorded section by section. Then, a polynomial surface fitting is applied to reconstruct the shape of rotating blade, including the analysis of measurement precision based on the Kline–McClintock method. The results from deformation testings show that nose-down torsion is generated in each flight mode. The data from a Fluid Structure Interaction model agrees well with experimental results at an acceptable level in terms of the trend predictions.

Next generation sequencing technologies, like ultra-deep pyrosequencing (UDPS), allows detailed investigation of complex populations, like RNA viruses, but its utility is limited by errors introduced during sample preparation and sequencing. By tagging each individual cDNA molecule with barcodes, referred to as Primer IDs, before PCR and sequencing these errors could theoretically be removed. Here we evaluated the Primer ID methodology on 257,846 UDPS reads generated from a HIV-1 SG3Δenv plasmid clone and plasma samples from three HIV-infected patients. The Primer ID consisted of 11 randomized nucleotides, 4,194,304 combinations, in the primer for cDNA synthesis that introduced a unique sequence tag into each cDNA molecule. Consensus template sequences were constructed for reads with Primer IDs that were observed three or more times. Despite high numbers of input template molecules, the number of consensus template sequences was low. With 10,000 input molecules for the clone as few as 97 consensus template sequences were obtained due to highly skewed frequency of resampling. Furthermore, the number of sequenced templates was overestimated due to PCR errors in the Primer IDs. Finally, some consensus template sequences were erroneous due to hotspots for UDPS errors. The Primer ID methodology has the potential to provide highly accurate deep sequencing. However, it is important to be aware that there are remaining challenges with the methodology. In particular it is important to find ways to obtain a more even frequency of resampling of template molecules as well as to identify and remove artefactual consensus template sequences that have been generated by PCR errors in the Primer IDs.

A wide range of experimental results carried out in low enthalpy facilities is used to sustain simple correlations predicting heat transfer rates on an attachment line in hypersonic flow. It is observed that for long swept cylinders a nearly asymptotic state can be reached for which transition Reynolds number does not change substantially quite far from the apex of the cylinder. Intermittency based on measured heat fluxes was used to describe the laminar-turbulent process. Prediction of turbulent heat transfer rates is established using a reference temperature method that provides quick and relatively accurate estimates for a wide range of Mach number and temperature ratio.

The behavior of engineering systems arises as a direct result of interactions and interfaces between components. Whereas many of these intercomponent dependencies are easily identifiable, many others are obscure, often occurring as a res tilt of technical interactions between remote entities. The identification and management of system interactions forms a major part of the systems engineering practices for system architecture, but methodologies for effective identification and management of interactions arising as a result of technical interfaces are still problematic. A methodology is developed for aircraft systems that identifies analysis-dependent system linkages. The result is the capability to assess the effect of analysis fidelity on system design.

The work presented is concerned with the estimation of manufacturing cost at the concept design stage, when little technical information is readily available. The work focuses on the nose cowl sections of a wide range of engine nacelles built at Bombardier Aerospace Shorts of Belfast. A core methodology is presented that: defines manufacturing cost elements that are prominent; utilises technical parameters that are highly influential in generating those costs; establishes the linkage between these two; and builds the associated cost estimating relations into models. The methodology is readily adapted to deal with both the early and more mature conceptual design phases, which thereby highlights the generic, flexible and fundamental nature of the method. The early concept cost model simplifies cost as a cumulative element that can be estimated using higher level complexity ratings, while the mature concept cost model breaks manufacturing cost down into a number of constituents that are each driven by their own specific drivers. Both methodologies have an average error of less that ten percent when correlated with actual findings, thus achieving an acceptable level of accuracy. By way of validity and application, the research is firmly based on industrial case studies and practice and addresses the integration of design and manufacture through cost. The main contribution of the paper is the cost modelling methodology. The elemental modelling of the cost breakdown structure through materials, part fabrication, assembly and their associated drivers is relevant to the analytical design procedure, as it utilises design definition and complexity that is understood by engineers.

The article presents cost modeling results from the application of the Genetic-Causal cost modeling principle. Industrial results from redesign are also presented to verify the opportunity for early concept cost optimization by using Genetic-Causal cost drivers to guide the conceptual design process for structural assemblies. The acquisition cost is considered through the modeling of the recurring unit cost and non-recurring design cost. The operational cost is modeled relative to acquisition cost and fuel burn for predominately metal or composites designs. The main contribution of this study is the application of the Genetic-Causal principle to the modeling of cost, helping to understand how conceptual design parameters impact on cost, and linking that to customer requirements and life cycle cost.

The physics of the plume-induced shock and separation, particularly at high plume to exit pressure ratios with and without shock-turbulent boundary-layer control methods, were studied using computational techniques. Mass-averaged Navier-Stokes equations with a two-equation turbulence model were solved by using a fully implicit finite volume scheme and time.marching algorithm. The control methodologies for shock interactions included a porous tail and a porous extension attached at the nozzle exit or trailing edge. The porous tail produced a weaker shock and fixed the shock position on the control surface. The effect of the porous extension on shock interactions was mainly to restrain the plume from strongly underexpanding during a change in flight conditions. These techniques could give an additional dimension to the design and control of supersonic missiles.

reverser considered in this paper uses the natural blockage concept, with only the fan duct flow being reversed. This paper focuses on the study of the aerodynamic performance of the cascade within a cold stream thrust reverser. Aerodynamic simulations are carried out using realistic operating conditions, for idealized cascade models representing three design options. The aim of this work is to investigate whether the aerodynamic performance of the thrust reverser cascade has been improved while minimizing weight of the cascade. In addition, t1his is the first attempt of us to considering noise reduction during design of the thrust reverse. The numerical simulations show that despite a reduction in total reverse thrust for the weight reduced designs, the supersonic flow regime, which existed in the original design, was eliminated after changing vane configurations made with the 5% and 10% weight reductions. The aerodynamic performance around the cascade and in the fan duct within the thrust reverser has been improved. Moreover, the acoustic characteristics of the thrust reverser are improved too. The total reverse thrust is not significantly affected with the modified cascade.

Plume interference effects on the axisymmetric flowfields around powered missiles are investigated using computational techniques. The study is mainly to understand the physics of the plume-induced shock and separation particularly at high plume to exit pressure ratios with and without shock-turbulent boundary layer control methods. Mass-averaged Navier-Stokes equations with the RNG k-ε turbulence model are solved using a fully implicit finite volume scheme and time-marching algorithm. The shock position and extent of separation was found to be dependent on the freestream Mach number and plume pressure ratio. Rounding the tail or a groove on the surface near the tail moved the shockwave downstream of the tail fin which should enhance the control of the missile.

International audience; This paper is concerned with the evaluation of design techniques, both for the propulsive performance and for the structural behavior of a composite flexible proprotor. A numerical model was developed using a combination of aerodynamic model based on Blade Element Momentum Theory (BEMT), and structural model based on anisotropic beam finite element, in order to evaluate the coupled structural and the aerodynamic characteristics of the deformable proprotor blade. The numerical model was then validated by means of static performance measurements and shape reconstruction from Laser Distance Sensor (LDS) outputs. From the validation results of both aerodynamic and structural model, it can be concluded that the numerical approach developed by the authors is valid as a reliable tool for designing and analyzing the UAV-sized proprotor made of composite material. The proposed experiment technique is also capable of providing a predictive and reliable data in blade geometry and performance for rotor modes.

International audience; Ionic polymer-metal composites have been widely used as actuators for robotic systems. In this article, we investigate and verify the characteristics of ionic polymer-metal composite actuators experimentally and theoretically. Two analytical models are utilized to analyze the performance of ionic polymer-metal composites: a linear irreversible electrodynamical model and a dynamic model. We find that the first model accurately predicts the static characteristics of the ionic polymer-metal composite according to the Onsager equations, while the second model is able to reveal the back relaxation characteristics of the ionic polymer-metal composite. We combine the static and dynamic models of the ionic polymer-metal composite and derive the transfer function for the ionic polymer-metal composite's mechanical response to an electrical signal. A driving signal with a smooth slope and a low frequency is beneficial for the power efficiency.

International audience; A passive twist control is considered as an adaptive way to maximize the overall efficiency of a proprotor developed for convertible Micro Air Vehicles. The varied operation conditions suggest different twist distributions for hover and forward flight with the constraint of identical planform. In this work, adaption of the proprotor geometry is achieved by centrifugal force induced twist. Classical Lamination Theory is used to predict structural loads, while Blade Element Momentum Theory is employed to understand the aerodynamic benefits of adaptive proprotor as applied on Micro Air Vehicles. Tip mass is proposed to increase the stability and generate negative torsion for rotating blade. Validation of the procedure is based on measurements of blade deformation, performed by laser displacement sensors. While negative torsion is found in both rotor and propeller modes, level of deformation is still below what is required for optimum dual operation.

Application of drag reduction technology based on laminar flow in a commercial environment is still being hindered by unanswered questions regarding its operational reliability. The encounter of ice crystals, as occurring in cirrus cloud, is known to result in performance degradations or even a temporary complete loss of laminar flow. Actually occurring mechanisms are not well understood and previously proposed critical parameters have not yet been verified experimentally. Difficulties encountered while attempting to recreate conditions in the laboratory that are representative of the real occurrences have led to the development and design of several alternative experimental methods. This study presents results from a relatively simple method, in terms of its complexity, providing for further insight into the phenomenon of a small particle being capable of producing a turbulent event while passing through an initially laminar boundary layer. Using this method, for a smooth spherical particle, a critical Reynolds number of approximately 300 has been determined above which the generation of a turbulent-spot-like disturbance will occur.

We generalize here the classical stochastic substitution models of nucleotides to genetic motifs of any size. This generalized model gives the analytical occurrence probabilities of genetic motifs as a function of a substitution matrix containing up to three formal parameters (substitution rates) per motif site and of an initial occurrence probability vector of genetic motifs. The evolution direction can be direct (past-present) or inverse (present-past). This extension has been made due to the identification of a Kronecker relation between the nucleotide substitution matrices and the motif substitution matrices. The evolution models for motifs of size 4 (tetranucleotides) and 5 (pentanucleotides) are now included in the SEGM (Stochastic Evolution of Genetic Motifs) web server.