This investigation sought first to determine the feasibility of generating a surrogate model of the interference drag between nacelles and wing-fuselage systems suitable for the inclusion in a multidisciplinary design optimization (MDO) framework. The target aircraft was a single-aisle, transonic aircraft with a freestream Mach number of 0.8 at 35,000 feet and a design lift coefficient of 0.5. Using an MDO framework is necessary for placing the nacelle because of the competing objectives of the disciplines involved in aircraft design including structures, acoustics, and aerodynamics. A secondary goal was to determine what tools are necessary for accurately capturing interference drag effects on the system. This research used both Euler computational fluid dynamics (CFD) with a coupled viscous drag estimation tool and Reynolds Averaged Navier-Stokes (RANS) CFD to estimate the system drag. The initial trade space exploration that varied the nacelle location across a baseline airframe configuration was completed with the Euler solver, and it showed that appreciable overlap between the wing and nacelle led to large increases in interference drag. A follow-on study was conducted with RANS CFD where the wing shape was tailored for each unique nacelle position. In comparing the results of the Euler and the RANS CFD, it was determined that RANS is required to accurately capture the flow features. Euler solvers can create artifacts due to the lack of viscous effects within the model. Wing tailoring is necessary because of the sensitivity of transonic flows to geometric changes and the addition of neighboring components, such as a nacelle. The research showed that for above and aft wing locations, a nacelle can overlap the trailing edge without incurring a drag penalty. Nacelles placed in the conventional location, forward and beneath the wing, displayed low interference drag effects, as the nacelle had a small and local impact on the wing's aerodynamics. Given the high cost of computing a RANS solution with wing tailoring, and the large design space for nacelle locations, building a surrogate model for interference drag was found to be prohibitive at this time. As the cost of computing and mesh generation decreases, collecting the data for building a surrogate model may become tractable. / Doctor of Philosophy / Engine placement on an aircraft is dependent on multiple disciplines. Engine placement affects the noise of the aircraft because the wing can shield or reflect the engine noise. Engine placement impacts the structural loads of an aircraft, with some positions requiring more reinforcement that adds to the cost and weight of the aircraft. Aerodynamically, the engine placement impacts the vehicle's drag. Taken together, the only means of trading the different disciplines' needs is through a multidisciplinary design optimization (MDO) framework. The challenge of MDO frameworks is that they require numerous solutions to effectively explore the trade space. Thus, MDO frameworks employ fast, low-order tools to compute hundreds or thousands of different combinations of features. A common approach to make running MDO analysis feasible is to develop surrogate models of the key considerations. Current aerodynamic drag build-ups for aircraft do not consider the interference drag associated with engine placement. The first goal of this research was to determine the feasibility of generating a surrogate model for inclusion in an MDO framework. In order to collect the data required for the surrogate, appropriate tools to capture the interference drag are required. Building a surrogate requires a large number of samples, thus the aerodynamic solver must be fast, robust, and accurate. An Euler (inviscid) computational fluid dynamics (CFD) was used do explore the engine placement design space to test the feasibility of building the surrogate model. The target aircraft was a single-aisle, transonic aircraft with a freestream Mach number of 0.8, flying at an altitude of 35,000 feet and a design lift coefficient of 0.5. The initial vehicle used a baseline wing, and the engine placement was varied across the wing span and fuselage. The results showed that the conventional location, where the engine is forward and beneath the wing, had the a modestly beneficial interference drag, though positions near the trailing edge and above the wing also showed neutral interference drag. In general, if the engine overlapped the wing, the interference drag increased dramatically. A follow-on study used Reynolds Averaged Navier-Stokes (RANS) CFD to investigate seven engine placements above and aft of the wing. Each of these positions had the wing tailored such that the wing performance would be typical of a good transonic wing. The results showed that with wing tailoring, a moderate amount of overlap between the wing and nacelle results in reduced or neutral interference drag. This is in contrast with the baseline wing results that showed moderate overlap led to large increases in interference drag. The results from this research suggest that building a surrogate model of interference drag for transonic aircraft is not feasible given today's computational resources. In order to accurately model the interference drag, one must use a RANS CFD solver and tailor the wing. These requirements increase the cost of evaluating an engine position such that collecting enough for a surrogate model is prohibitively expensive. As computational speeds increase, and the ability to automate CFD mesh generation becomes less time intensive, the feasibility may increase. Using an Euler solver is insufficient because of the lack of viscous effects in the flow. The lack of a boundary layer leads to artifacts appearing in the flow when the nacelle and wing are in close proximity.

A decomposition methodology based on the concept of "thermoeconomic isolation" applied to the synthesis/design and operational optimization of an advanced tactical fighter aircraft is the focus of this research. Conceptual, time, and physical decomposition were used to solve the system-level as well as unit-level optimization problems. The total system was decomposed into five sub-systems as follows: propulsion sub-system (PS), environmental control sub-system (ECS), fuel loop sub-system (FLS), vapor compressor and PAO loops sub-system (VC/PAOS), and airframe sub-system (AFS) of which the AFS is a non-energy based sub-system. Configurational optimization was applied. Thus, a number of different configurations for each sub-system were considered. The most promising set of candidate configurations, based on both an energy integration analysis and aerodynamic performance, were developed and detailed thermodynamic, geometric, physical, and aerodynamic models at both design and off-design were formulated and implemented. A decomposition strategy called Iterative Local-Global Optimization (ILGO) developed by Muñoz and von Spakovsky was then applied to the synthesis/design and operational optimization of the advanced tactical fighter aircraft. This decomposition strategy is the first to successfully closely approach the theoretical condition of "thermoeconomic isolation" when applied to highly complex, highly dynamic non-linear systems. This contrasts with past attempts to approach this condition, all of which were applied to very simple systems under very special and restricted conditions such as those requiring linearity in the models and strictly local decision variables. This is a major advance in decomposition and has now been successfully applied to a number of highly complex and dynamic transportation and stationary systems. This thesis work presents the detailed results from one such application, which additionally considers a non-energy based sub-system (AFS). / Master of Science

Methods were developed for the design of a solar powered UAV capable of tracking the sun to achieve maximum solar energy capture. A single-axis solar tracking system was designed and constructed. This system autonomously rotated an onboard solar panel to find the angle of maximum solar irradiance while the UAV was airborne. A microcontroller was programmed and implemented to control the solar tracking system. A solar panel and an efficient airframe capable of housing the solar tracking system was designed and constructed. Each of these subsystems was tested individually with either ground or flight tests. Ultimately, the final assembled system was tested. These tests were used to determine where and when a UAV with an onboard solar tracker would be advantageous over a conventional solar powered UAV with PV cells statically fixed to its wings. The final UAV had a wingspan of 3.2 meters, a length of 2.6 meters, and weighed 4.1 kilograms. Its solar panel provided a maximum power output of 37.7 watts. The predicted system performance, airframe drag, and system power requirements were validated with a battery powered flight test. The UAV's analytical model predicted the drag to be 41% lower than the actual drag found from flight testing. Full system functionality was verified with a solar powered flight test. The results and analysis of the system tests are presented in this thesis. The net energy increase from the solar tracking UAV over a conventional solar powered UAV for the duration of a day is dependent on season and geographical location. The solar tracking UAV that was developed was found to have a maximum net energy gain of 34.5% over a conventional solar powered version of the UAV. The minimum net energy gain of the solar tracking UAV was found to be 0.8%.

Due to a trend towards Ultra High Bypass Ratio engines the corresponding engine/airframe interference is becoming a key aspect in aircraft design. The present economic situation increases the pressure on commercial aviation companies to reduce the Direct Operating Cost, and the environmental situation requires a new generation of aircraft with a lower environmental impact. Therefore detailed aerodynamic investigations are required to evaluate the real benefits of new technologies. The presented research activity is part of a long-term project with the main objective of generating a reliable and accurate tool to predict the performance of an aircraft over the whole flight domain. In particular the aim of this research was to perform advanced CFD in order to establish a tool able to evaluate engine installation effects for different configurations and attitudes. The developed tool can be provided with correlations of the Net Propulsive Force (NPF), the force exerted by the power-plant to the aircraft, as a function of position. This can be done in principle at cruise, hold, climb, descent, take-off and landing, to model the different integration effects at different phases. Due to the complexity of the problem it was only possible at an initial stage to determine these correlations at cruise condition. Two parametric test cases were evaluated, showing that the engine horizontal positioning can influence the mission fuel burn by up to 6.4%. According to the extensive literature review that has been done, this study can be regarded as the first open literature engine position-NPF parametric study using CFD. Even though no correlations were extracted for other conditions; a deployed high-lift wing configuration was also studied in detail, defining the main aerodynamics effects of the engine integration at high angle of attack. A topological study of the high-lift installation vortices is presented in this work and it can be considered the first in the open literature. It should be pointed out that extensive research is currently underway to correctly evaluate the high-lift aerodynamic using CFD. The Propulsive System Integration (PSI) in high-lift conditions is adding flow features to an already demanding problem, making it a real challenge for the numerical methods. Nevertheless the additional effects of a nacelle chine on the maximum lift were also evaluated. The main outcomes of this PhD research were: a coupled performance modelling tool able to handle the effects of engine-airframe integration as a function of geometry and attitude, and a topological study of the high-lift installation vortices. During the course of the work, this research was successfully suggested as an extra activity for the European NEWAC project (New Aero Engine Core Concepts), and resulted in a new deliverable for that project.

Composite structures can lower the weight of an airliner significantly. Due to the higher process complexity and the high material cost, however, the low weight often comes with a significant increase in production cost. The application of cost-effective design strategies is one mean to meet this challenge. In this thesis, a simplified form of direct operating cost is suggested as a comparative value that in combination with multidisciplinary optimization enables the evaluation of a design solution in terms of cost and weight. The proposed cost optimization framework takes into account the manufacturing cost, the non-destructive testing cost and the lifetime fuel consumption based on the weight of the aircraft, thus using a simplified version of the direct operating cost as the objective function. The manufacturing cost can be estimated by means of different techniques. For the proposed optimization framework, feature-based parametric cost models prove to be most suitable. Paper A contains a parametric study in which a skin/stringer panel is optimized for a series of cost/weight ratios (weight penalties) and material configurations. The weight penalty (defined as the specific lifetime fuel burn) is dependent on the fuel consumption of the aircraft, the fuel price and the viewpoint of the optimizer. It is concluded that the ideal choice of the design solution is neither low-cost nor low-weight but rather a combination thereof. Paper B proposes the inclusion of non-destructive testing cost in the design process of composite components, and the adjustment of the design strength of each laminate according to inspection parameters. Hence, the scan pitch of the ultrasonic testing is regarded as a variable, representing an index for the guaranteed material quality. It is shown that the cost for non-destructive testing can be lowered if the quality level of the laminate is assigned and adjusted in an early design stage. In Paper C and Paper D the parameters of the manufacturing processes are upgraded during the cost optimization of the component. In Paper C, the framework is extended by the cost-efficient adaptation of parameters in order to reflect the situation when machining an aluminum component. For different weight penalties, the spar thickness and stringer geometry of the provided case study vary. In addition, another cutter is chosen with regard to the modified shape of the stringer. In Paper D, the methodology is extended to the draping of composite fabrics, thus optimizing not only the stacking layup, but also the draping strategy itself. As in the previous cases, the design alters for different settings of the weight penalty. In particular, one can see a distinct change in fiber layup between the minimum weight and the minimum cost solution. Paper E summarizes the work proposed in Papers A-D and provides a case study on a C-spar component. Five material systems are used for this case study and compared in terms of cost and weight. The case study shows the impact of the weight penalty, the material cost and the labor rate on the choice of the material system. For low weight penalties, for example, the aluminum spar is the most cost-effective solution. For high weight penalties, the RTM system is favorable. The paper also discusses shortcomings with the presented methodology and thereby opens up for future method developments. / QC 20100723 / European Framework Program 6, project ALCAS, AIP4-CT-2003-516092 / Nationella flygtekniska forskningsprogrammet (NFFP) 4, project kostnadseffektiv kompositstruktur (KEKS)

Due to a trend towards Ultra High Bypass Ratio engines the corresponding engine/airframe interference is becoming a key aspect in aircraft design. The present economic situation increases the pressure on commercial aviation companies to reduce the Direct Operating Cost, and the environmental situation requires a new generation of aircraft with a lower environmental impact. Therefore detailed aerodynamic investigations are required to evaluate the real benefits of new technologies. The presented research activity is part of a long-term project with the main objective of generating a reliable and accurate tool to predict the performance of an aircraft over the whole flight domain. In particular the aim of this research was to perform advanced CFD in order to establish a tool able to evaluate engine installation effects for different configurations and attitudes. The developed tool can be provided with correlations of the Net Propulsive Force (NPF), the force exerted by the power-plant to the aircraft, as a function of position. This can be done in principle at cruise, hold, climb, descent, take-off and landing, to model the different integration effects at different phases. Due to the complexity of the problem it was only possible at an initial stage to determine these correlations at cruise condition. Two parametric test cases were evaluated, showing that the engine horizontal positioning can influence the mission fuel burn by up to 6.4%. According to the extensive literature review that has been done, this study can be regarded as the first open literature engine position-NPF parametric study using CFD. Even though no correlations were extracted for other conditions; a deployed high-lift wing configuration was also studied in detail, defining the main aerodynamics effects of the engine integration at high angle of attack. A topological study of the high-lift installation vortices is presented in this work and it can be considered the first in the open literature. It should be pointed out that extensive research is currently underway to correctly evaluate the high-lift aerodynamic using CFD. The Propulsive System Integration (PSI) in high-lift conditions is adding flow features to an already demanding problem, making it a real challenge for the numerical methods. Nevertheless the additional effects of a nacelle chine on the maximum lift were also evaluated. The main outcomes of this PhD research were: a coupled performance modelling tool able to handle the effects of engine-airframe integration as a function of geometry and attitude, and a topological study of the high-lift installation vortices. During the course of the work, this research was successfully suggested as an extra activity for the European NEWAC project (New Aero Engine Core Concepts), and resulted in a new deliverable for that project.

Cette thèse étudie des méthodes de conception aérodynamique pour les avions de ligne de demain. A l'heure actuelle, les avions de ligne sont en général conçus de manière à ce que les moteurs, conçus séparément du reste de l'aéronef, n'interagissent que très peu avec la cellule de l'avion (la voilure, le fuselage,...). Pour diminuer la consommation de carburant, de nouveaux concepts comme l'ingestion de couche limite émergent, dans lesquels l'avion est conçu pour tirer profit des interactions aérodynamiques qui peuvent s'établir entre le moteur et la cellule de l'avion sur certaines configurations. Il devient alors nécessaire de simuler ces interactions pour s'assurer que le bénéfice pour l'avion en termes de consommation de carburant est réel. La méthode développée dans cette thèse a pour objectif de rendre possible la simulation de ces interactions, à un coût de calcul qui reste acceptable. La soufflante, qui est l'élément du moteur le plus à même d'interagir avec l'avion, est modélisée à l'aide d'un champ de force qui reproduit son aspiration de l'écoulement d'air. Cette approche permet de reproduire les interactions aérodynamiques entre l'avion et ses moteurs à un coût 50 fois inférieur à celui d'une simulation complète du moteur et de l'avion, ce qui permettra en pratique d'optimiser les lignes aérodynamiques des futurs avions. / This work explores new méthodologies for the aerodynamic conception of future commercial aircraft. In general, commercial aircraft are designed to limit aerodynamic interactions between the engines and the airframe. New aircraft concepts such as boundary layer ingestion are now studied, in which the aircraft is designed to take advantage of these interactions. It is then necessary to be able to simulate these interactions to ensure that real benefits in terms of aircraft fuel burn are possible. The methodology that is developed in the présent thesis aims at enabling the simulation of these aerodynamic interactions at affordable computational cost. The fan, which is the part of the engine the most likely to internet with the airframe, is modeled using a force field that reproduces the suction of the air inside the engine. This approach allows to reproduce fan- airframe interactions at a fraction of the cost of a complété simulation of the aircraft and the engines, and enable the practical optimization of the aerodynamic performance of future aircraft.

ABSTRACTThe purpose of this thesis is to design and analyze the new generation leading edge slat of a commercial jet to reduce the structural noise with the application of new conceptual design approaches. Recent scientific research show that the leading edge slats account for the structural noise during the flight operation therefore, when the leading edge slat is deployed under different flight conditions, an open gap/slot is formed between the high lift device and the wing box. However, since the leading edge slat includes flexible sections, it is assumed that defining an adaptive system inside the leading edge slat may reduce the structural noise by utilizing bending properties of these flexible sections. Hence, electromechanical actuator designing gains also great importance in the whole process. In this study, we have used, finite element modelling of the slat structure to examine the required structural deformations and strengths; our work is based on the software ANSYS/Workbench. To be realistic in deciding the right geometry in the follow up steps, we have first studied a generic geometry having no aerodynamics or actuator forces application. The whole simulation was performed by defining dummy forces and dummy material properties. The simulation lead to having a global overview of the mechanical behaviour of the structure; further, once the influent parameters were tested, realistic aerodynamic forces and material properties were defined, and as a result of bending of the flexible sections the required gap closure was formed between the trailing edge of the slat and the wing box. Subsequently, the suitable actuator design and required strength analysis are also performed on the last section. This study has also proved that the use of adaptive systems on the leading edge slats improves flight comfort by reducing the structural noise and provides less fuel consumption; this is significant for the long run considerations of aeroplane manufacturers. / es Zentrum für Luft- und Raumfahrt e. V. (DLR)

Foi realizado um estudo comparativo da capacidade de duas variantes do método de radiografia por raios- X em detectar trincas de fadiga em juntas sobrepostas rebitadas de laminado híbrido metal-fibra Glare® de uso aeronáutico. Durante os ensaios mecânicos de fadiga sob amplitude constante de tensão, diversos corpos de prova rebitados foram periodicamente inspecionados por raios-X, em ambas as modalidades convencional e digital. Raios-X em filmes convencionais digital. Raios-X em filmes convencionais proporcionaram ótimo detalhamento de trincas nas juntas mecânicas, enquanto que as imagens geradas pela modalidade digital apresentaram qualidade muito inferior, prejudicando ou até mesmo impedindo a avaliação do grau de integridade estrutural das juntas rebitadas. / A comparison is performed on the ability of two modalities of nondestructive X-ray radiography method in detecting fatigue cracks in riveted lap joints of aeronautical grade fiber-metal laminate Glare™. During constant amplitude loading in fatigue testing riveted specimens were periodically inspected using both the conventional and digital X-ray methodology. Conventional film X-ray modality provided high quality images of growing cracks in the mechanical joints, whereas digital radiography generated faulty images, which impaired or even prevented the structural integrity assessment of the riveted joints.

Strides in modern computational fluid dynamics and leaps in high-power computing have led to unprecedented capabilities for handling large aerodynamic problem. In particular, the emergence of adjoint design methods has been a break-through in the field of aerodynamic shape optimization. It enables expensive, high-dimensional optimization problems to be tackled efficiently using gradient-based methods in CFD; a task that was previously inconceivable. However, adjoint design methods are intended for gradient-based optimization; the curse of dimensionality is still very much alive when it comes to design space exploration, where gradient-free methods cannot be avoided. This research describes a novel approach for reducing dimensionality in large, computationally expensive design problems to a point where gradient-free methods become possible. This is done using an innovative application of Principal Component Analysis (PCA), where the latter is applied to the gradient distribution of the objective function; something that had not been done before. This yields a linear transformation that maps a high-dimensional problem onto an equivalent low-dimensional subspace. None of the original variables are discarded; they are simply linearly combined into a new set of variables that are fewer in number. The method is tested on a range of analytical functions, a two-dimensional staggered airfoil test problem and a three-dimensional Over-Wing Nacelle (OWN) integration problem. In all cases, the method performed as expected and was found to be cost effective, requiring only a relatively small number of samples to achieve large dimensionality reduction.