Preventing ice accumulation on aircraft surfaces is important to maintain safe operation during flight. Ice accumulation on aero-engine nose cones is detrimental as large pieces may break off and be ingested into the engine damaging the compressor blades. Currently, hot bleed air is taken from the compressor and blown over the inside and outside surfaces of the nose cone to prevent ice formation on the surface. Although effective, this technique reduces the efficiency of the aero-engine. This investigation evaluates the performance of a novel anti-icing system that uses a rotating heat pipe to transfer heat from the engine to the nose cone. Rotating heat pipes are effective two-phase heat transfer devices capable of transporting large amounts of heat over small temperature differences and cross-sectional areas. In this system, waste heat that is generated in the engine would be transferred to the rotating heat pipe at an evaporator and then transferred into the critical areas of the nose cone at a condenser preventing ice accumulation on the outside surface. In this investigation, the heat is transferred into the heat pipe from a fluid heated by the engine that would pass through a small annular gap between the rotating heat pipe and a stationary wall. The heat transfer for this configuration and the effect of passive heat transfer augmentation on the outside of the rotating heat pipe in the jacket was investigated experimentally for a range of Taylor numbers of 10^6 < Ta < 5x10^7 and for axial Reynolds numbers of 900 < Re_x < 2100, characteristic of this configuration when engine lubricant was used as the working fluid. It was found that by using an array of three-dimensional cubical protrusions, the heat transfer in the evaporator could be increased by 35% to 100%. This result was better than that found using two-dimensional rib roughness. It was also found that the evaporator performance was a limiting factor in the heat transfer performance of the system under most conditions, so further optimization of the evaporator is important. In the proposed condenser design, the condenser section of the rotating heat pipe would be encased in a lightweight, high conductivity polycrystalline graphite or similar composite material and the end of the heat pipe would be in direct contact with the nose cone. It was found that the end-wall of the heat pipe was not a source of high heat transfer, however it provided an effective means for heating the tip of the nose cone. The effect of using heating channels on the inside of the nose cone was also considered. Here, the condensate from the rotating heat pipe was driven through small radially spaced channels on the inside surface of the nose cone. The heating channels were found to be ineffective due to the small contact area that could be made with the nose cone. This was a result of the limited condensate flow that occurs in rotating heat pipes. The heat transfer through the proposed system was 700W to 1100W using water and 400W to 800W using ethanol in the heat pipe. It was found that 50% to 75% of the arclength of the nose cone could be maintained above 0°C using water in the heat pipe at an ambient temperature of -30°C and an airplane speed of 300 km/h. This arclength decreased to approximately 25% when ethanol was used as the working fluid. An increase in airplane speed reduced this arclength maintained above 0°C significantly. / Thesis / Master of Applied Science (MASc)

Multidisciplinary design optimization (MDO) is a technique that has found use in the field of aerospace engineering for aircraft design. It uses optimization to simultaneously solve design problems with several disciplines involved. In order to predict aircraft performance an engine performance simulation model, also called “rubber engine”, is vital. The goal of this project is to validate and integrate a rubber engine model into an MDO environment. A method for computer simulation of gas turbine aero engine performance was created. GasTurb v11, a commercial gas turbine performance simulation software, was selected for doing the simulation models. The method was validated by applying it to five different jet engines of different size, different type and different age. It was shown that the simulation engine model results are close to the engine manufacturer data in terms of SFC and net thrust during cruise, maximum climb (MCL) and take off (MTO) thrust ratings. The cruise, take off and climb SFC was in general predicted within 2% error when compared to engine manufacturer performance data. The take off and climb net thrust was in general predicted with less than 5% error. The integration of the rubber engine model with the MDO framework was started and it was demonstrated that the model can run within the MDO software. Four different jet engine models have been prepared for use within the optimization software. The main conclusion is that GasTurb v11 can be used to make accurate jet engine performance simulation models and that it is possible to incorporate these models into an MDO environment.

No description available.

Carbon fibre reinforced polymer (CFRP) composite materials exhibit high specificstrength and stiffness therefore they can be a lightweight alternative to metalliccomponents for the front section of an aero-engine. Despite the benefit of CFRP composite materials for aero-engine applications, there arealso new challenges due to their inherent properties compared to conventionalaerospace metallic structures, such as a lower erosion resistance, poor thermalresistance, and poor electrical conductivity. In aero-engines, some components can be subjected to harsh erosive environmentsduring operation, therefore the erosion resistance of CFRP composite materials need tobe investigated. CFRP composites are not able to withstand as high temperatures astraditional metallic components and their ability to resist fire events need to beenhanced. On the other side, the poor electrical conductivity of CFRP composites canalso be critical when the aircraft is struck by lightning. Therefore, improving theconductivity of CFRP composite is of large interest. This thesis work is focusing on investigating innovative coating solutions to overcomethese three independent challenges in order to enhance CFRP composite applicationsinto the front section of an aero-engine. Coating systems for lightning strike protection have been investigated and developed.A fire protection has been identified and tested; the tests showed promising results forfire application. Furthermore, investigations on erosion resistant coatings indicated thepossible improvement of replacing the currently used erosion resistant coating by othercoatings presented in this thesis work.

Servo valves are used in a broad variety of flow modulation applications. In the field of aerospace, servo valves are used in aero engines to meter fuel flow. The existing valves are labour intensive to manufacture and highly optimised such that to achieve improvements in performance requires a novel design. This research investigates smart material actuators and valve concepts. Specifically, a prototype pilot stage nozzle flapper valve is developed for the purpose of actuating a main stage spool. The typical nozzle flapper type servo valve uses a torque motor to actuate the flapper. In this research project, the torque motor has been substituted for two piezoelectric ring bender actuators. A novel mounting mechanism has been developed to secure the ring benders within the valve. Analytical and finite element models have been made to understand the displacement mechanism of a ring bender and the effects of the mount on the displacement and force from a ring bender, and the results were compared with experiment. The mounting stiffness at the inner and outer edges was found to decrease the displacement of the ring bender and it was found that the stiffness of the mount at the outer edge has a greater negative effect on displacement than the stiffness of the mount at the inner edge. The displacement of a ring bender was tested across the operational temperature range of an aero engine. It was found that the displacement of the ring bender is reduced at low temperatures and increases at high temperature. The variation of stiffness of the elastomeric mount was also tested with temperature and it was found that the displacement of a ring bender is significantly reduced when the mounting elastomer approaches its glass transition temperature. A prototype valve was built to test the pressures and flows that could be achieved at two control ports by using a ring bender as actuator. A single ring bender and two ring benders, mounted in tandem to provide redundancy, have been tested. An analytical model was developed and the predictions are compared with experimental results for pressures and flow. The full stroke of the valve was 300m when mounted and reduced to 150m when mounted in tandem with an inactive ring bender. The hysteresis of the valve is +/-10%. The pressures and flow at and between the control ports of the valve are consistent with the predictions.

Aero-engine assemblies are complex structures typically involving two or three nested rotors mounted within a flexible casing via squeeze-film damper (SFD) bearings. The deployment of SFDs into such structures is highly cost-effective but requires careful calculation since they can be highly nonlinear in their performance, particularly if they are unsupported (i.e. without a retainer spring). The direct study of whole-engine models with nonlinear bearings has been severely limited by the fact that current nonlinear computational techniques are not well-suited for complex large-order systems. The main contributions of this thesis are: • A procedure for unbalance response computation, suitable for generic whole-engine models with nonlinear bearings, which significantly extends the capability of current finite element packages. This comprises two novel nonlinear computational techniques: an implicit time domain integator referred to as the Impulsive Receptance Method (IRM) that enables rapid computation in the time domain; a whole-engine Receptance Harmonic Balance Method (RHBM) for rapid calculation of the periodic response in the frequency domain. Both methods use modal data calculated from a one-off analysis of the linear part of the engine at zero speed.• First-ever analyses on real twin-spool and three-spool engines. These studies illustrate the practical use of these solvers, provide an insight into the nonlinear dynamics of whole-engines and correlate with a limited amount of industrial experimental data. Both IRM and RHBM are directly formulated in terms of the relative response at the terminals of the nonlinear bearings. This makes them practically immune to the number of modes that need to be included, which runs into several hundreds for a typical engine. The two solvers are extensively tested on two/three-shaft engine models (with 5-6 SFDs) provided by a leading engine manufacturer using an SFD model that is used in industry. The tests show the IRM to be many times faster than an established robust conventional implicit integrator while achieving a similar level of accuracy. It is also shown to be more reliable than another popular implicit algorithm. The RHBM enables, for the first time, the frequency domain computation of the nonlinear response of whole-engine models. Its use is illustrated for both Single-Frequency Unbalance (SFU) excitation (unbalance confined to only one shaft) and Multi-Frequency Unbalance (MFU) excitation (unbalance located on two or more shafts, rotating at different speeds). Excellent correlation is demonstrated between RHBM and IRM.The parametric studies compare and contrast the frequency spectra for SFU and MFU cases. They also reveal the varying degree of lift at the unsupported SFDs. The sensitivity of the response to end-sealing and bearing housing alignment is also illustrated. It is demonstrated that the use of suitably preloaded vertically oriented “bump-springs” at the SFDs of heavy rotors produces a significant improvement in journal lift. It is also shown that the consideration of a slight amount of distributed damping in the structure significantly affects the predicted casing vibration levels, bringing them closer to measured levels, while having little effect on the SFD orbits.

Environmental issues such as climate change are leading to important sustainability challenges in the aerospace industry. Composites are light materials that are extensively used to replace metals and reduce the aircraft weight, the goal being to decrease the fuel consumption in flight and limit the emission of greenhouse gases. However, these high performance materials are associated with a complex supply chain including energy-consuming processes. Most of the decommissioned composite products are currently landfilled and nothing proves that the weight reduction allowed by these materials compensates those negative aspects. The purpose of this master thesis is to determine if the introduction of composites in aero-engines can be sustainable and how it can be achieved. To do so, three polymer-matrix composite components from GKN Aerospace have been studied and compared with their metallic baseline from environmental, social and economic perspectives. Several options for materials selection, manufacturing processes and recycling possibilities have been investigated in the same way. The assessment on GKN Aerospace’s components showed that the weight savings provided by composites have a strong and positive influence on their sustainability. Component B shows the best results: with 16% of weight savings with composites versus the titanium baseline, it appears clearly that the composite version is the most sustainable one. Component A2 composite version also provides interesting weight savings (14%) but has an aluminum baseline, which makes the composite component more sustainable in some aspects but not all of them, especially economically speaking. Finally, for component A1, the composite version, which does not provide weight savings, is more economically feasible, but quite tight with the titanium baseline on environmental and social aspects. Therefore, it appears that composite components are more likely to be sustainable if they provide significant weight reduction and if the baseline is titanium. A few strategies would merit attention to make future composite components more sustainable. On the one hand, using thermoplastic composites have potential to reduce the environmental, social and economic impact. In fact, these materials can be fully recycled and reused, present less risks to handle and can be produced for a lower cost. Nevertheless, the knowledge on these materials is more limited than on thermoset composite and the implementation of such a solution will take time. On the second hand, introducing composite recycling processes in the products lifecycle can increase a lot the sustainability of composite components. The manufacturing scrap and the decommissioned products can both be recycled in order to reduce the environmental impact and generate benefits by re-using or selling the recycled material.

The subject of this PhD thesis is the development of an efficient system that can simultaneously pump and separate a gas-liquid mixture, in particular an oil-air mixture. Two-phase flows are encountered in many applications (petroleum extraction, flow in nuclear power plant pumps, pulp and paper processing, etc.) but this study is mainly focused on lubrication systems of aircraft gas turbine engines.<p><p>The pump and separator system (PASS) for two-phase flows developed in this PhD thesis aims to perform three functions simultaneously:<p>• Send back the oil to the tank (oil pumping)<p>• Separate the air from the oil (de-aeration)<p>• Separate the oil from the air (de-oiling) and release the sealing air into the atmosphere (venting). <p>Particular care is given to the liquid flow rate lost at the gas outlet of the system.<p>Consequently, it could replace the scavenge pumps and oil-air separators existing in present lubrication systems. This modification provides several advantages: simplification of the lubrication circuit, reduction of oil consumption and of the size of the lubrication system.<p><p>This research is divided into three axes: the theoretical study of the important physical mechanisms taking place inside the two-phase flow pump and separator system, the experimental development, tests and optimization of different PASS prototypes, and also the numerical simulations of the two-phase flow inside these prototypes. Although the experiments were the central pillar of this research, the three axes were closely imbricated.<p><p>The PASS design includes three main components:<p>• An inlet chamber with one or several tangential inlets giving a natural centrifugation to the flow,<p>• An impeller (forced centrifugation) with an axial and a radial part followed by a volute chamber,<p>• A metallic foam that lets pass micron and sub-micron droplets and which is followed by an axial vent port.<p><p>The centrifugation causes the liquid (oil) to move radially outwards in an annular body (a liquid ring) generating pressure. The thickness of this liquid ring inside the impeller is mainly determined by the pressure coefficient (related to the back-pressure and the rotational speed). When the back-pressure increases, the thickness of the liquid ring increases too. An advantage of the PASS is that it does not impose any relation between the liquid head and the liquid flow rate, contrary to common centrifugal pump. It self-regulates the radial position of the gas-liquid interface to sustain the operating conditions.<p><p>The de-aeration efficiency mainly depends on the pressure coefficient (for a constant liquid viscosity or temperature) or on the thickness of the liquid ring. The pressure gradient which appears in the liquid rotating in an annular body acts like a dam for the gas phase. Indeed, the gas movement is mainly determined by the pressure field (buoyancy) while the liquid distribution is dominated by centrifugal and Coriolis forces. Buoyancy tends to accumulate the gas phase near low pressure areas (PASS hub, suction side of the blades, clearances between closed impeller and casing).<p><p>The first oil-air PASS prototype produces high viscous losses due to the high peripheral velocity and liquid viscosity. Therefore, the pumping efficiency is poor compared to common impeller pumps. However, the pumping is not the key function of the PASS and a power consumption below 5 kW is acceptable for the application considered in this work. For applications that require lower power consumptions, a reduction of the rotational speed must be considered.<p><p>Thus, the rotational speed and the impeller diameter are two major constraints for the PASS design which determine the de-aeration and pumping efficiencies. The impeller diameter also influences the size of passage sections for the air flow. The air velocity must be kept as low as possible because the entrainment of droplets increases when the air velocity rises (drag forces on droplets). Indeed, this large influence of the air flow rate on the oil consumption (de-oiling efficiency) was demonstrated by a theoretical analysis, the experiments and the CFD simulations. The production of droplets in the inlet pipes when the two-phase flow is annular is a key phenomenon regarding the oil consumption.<p><p>In addition to the air flow rate, other variables also influence the oil consumption:<p>• Air-oil temperature: when the temperature rises, the oil consumption increases because the surface tension and the oil density are reduced. Moreover, as the air density also decreases, the air velocity rises.<p>• Oil flow rate: the oil consumption rises more or less linearly with the oil flow rate. However, the influence of the oil flow rate on the inlet droplet size is uncertain.<p>• Rotational speed: the rotational speed has obviously a strong impact on the oil consumption without metallic foam. However, experiments showed that the metallic foam efficiency is almost independent on the rotational speed. Therefore, the oil consumption with the Retimet foam does not depend on the PASS rotational speed.<p>• Altitude or air density: the oil consumption decreases when the air density is reduced because the drag forces on droplets also decrease.<p>The gas density (altitude) is also supposed to influence the de-aeration efficiency but this could not be tested or simulated in this work (the de-aeration efficiency gets probably better when decreasing the gas density because the buoyancy forces increase).<p><p>Theory, experiments and numerical simulations also allowed the prediction of performance of the first oil-air prototype for real in-flight operating conditions. Two problems have been identified: the de-aeration efficiency at MTO and cruise ratings and the oil leak throughout the vent in cold start and windmilling. To solve them, some modifications of the lubrication system have been suggested. With these modifications, the oil-air PASS should become very efficient and attractive for engine manufacturers. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

This thesis is a continuation of design automation studies within research projects financed by VINNOVA (the Swedish Governmental Agency for Innovation Systems) and Knowledge foundation that contributed to the development of producibility assessment system at a global aerospace products supplier, GKN Aerospace Sweden. A case study was carried at the company on Turbine Rear Structure (TRS) component design of a jet engine with the main objective to evaluate weld producibility assessment tools and to demonstrate system’s performance in multi-disciplinary design environment. The context of this thesis is a set-based product design development where several studies, i.e. thermal, structural, aerodynamic etc. are carried concurrently to gather knowledge between their parameter relations. The thesis contributes to the goal of fully integrated producibility assessment in multi-disciplinary studies to support product development process. The problems encountered during the thesis execution involved systematic analysis setup to extract and verify CAD geometry data, assessment of meaningfulness of producibility indicators, development of semi-automated data post-processing module and relating product design to its manufacturing aspects. Commercial and in-house developed software were used extensively to demonstrate the results of the system with the help of continuous company support to mitigate indispensable bottlenecks along the way. The work has led to systematic improvements, determined assessment limitations and most relevant weld producibility aspects. Collected feedback to evaluate prepared demonstrator showed promising results to support product design decisions considering both performance and producibility.

Dû aux efforts apportés à la réduction des émissions de NOx dans des chambres de combustion aéronautiques il y a une tendance récente vers des systèmes à combustion pauvre. Cela résulte dans l'apparition de nouveaux types d'injecteur qui sont caractérisés par une complexité géométrique accrue et par des nouvelles stratégies pour l'injection du carburant liquide, comme des systèmes multi-point. Les deux éléments créent des exigences supplémentaires pour des outils de simulation numériques. La simulation à grandes échelles (SGE ou LES en anglais) est aujourd’hui considérée comme la méthode la plus prometteuse pour capturer les phénomènes d'écoulement complexes qui apparaissent dans une telle application. Dans le présent travail, deux sujets principaux sont abordés : Le premier est le traitement de la paroi ce qui nécessite une modélisation qui reste délicate en SGE, en particulier dans des géométries complexes. Une nouvelle méthode d'implementation pour des lois de paroi est proposée. Une étude dans une géométrie réaliste démontre que la nouvelle formulation donne de meilleurs résultats comparé à l’implémentation classique. Ensuite, la capacité d'une approche SGE typique (utilisant des lois de paroi) de prédire la perte de charge dans une géométrie représentative est analysée et des sources d'erreur sont identifiés. Le deuxième sujet est la simulation du carburant liquide dans une chambre de combustion. Avec des méthodes Eulériennes et Lagrangiennes, deux approches sont disponibles pour cette tâche. La méthode Eulérienne considère un spray de gouttelettes comme un milieu continu pour lequel on peut écrire des équations de transport. Dans la formulation Lagrangienne, des gouttes individuelles sont suivies ce qui mène à des équations simples. D’autre part, sur le plan numérique, le grand nombre de gouttes à traiter peut s’avérer délicat. La comparaison des deux méthodes sous conditions identiques (solveur gazeux, modèles physiques) est un aspect central du présent travail. Les phénomènes les plus importants dans ce contexte sont l'évaporation ainsi que le problème d'injection d'un jet liquide dans un écoulement gazeux transverse ce qui correspond à une version simplifiée d’un système multi-point. Le cas d'application final est la configuration d’un seul injecteur aéronautique, monté dans un banc d'essai expérimental. Ceci permet d'appliquer de manière simultanée tous les développements préliminaires de ce travail. L'écoulement considéré est non-réactif mais à part cela il correspond au régime ralenti d'un moteur d'avion. Dû aux conditions préchauffées, le spray issu du système d'injection multi-point s'évapore dans la chambre. Cet écoulement est simulé utilisant les approches Eulériennes et Lagrangiennes et les résultats sont comparés aux données expérimentales. / Due to efforts to reduce NOx emissions of aeronautical combustors, there is a recent trend towards lean combustion technologies. This results in novel injector designs, which are characterized by increased geometrical complexity and new injection strategies for the liquid fuel, such as multipoint systems. Both elements create additional challenges for numerical simulation tools. Large-Eddy simulation (LES) is regarded as the most promising method to capture complex flow phenomena in such an application. In the present work, two main areas of interest are considered: The first is wall modeling, which remains a challenging field in LES, in particular for complex geometries. A new implementation method for wall functions that uses a no-slip condition at the wall is proposed. It is shown that in a realistic burner geometry the new formulation yields improved results compared to a classical implementation. Furthermore, the capability of a typical LES with wall models to predict the pressure drop in a representative geometry is assessed and sources of error are identified. The second topic is the simulation of liquid fuel in a combustor. With Eulerian and Lagrangian methods, two different approaches are available for this task. The Eulerian approach considers a droplet spray as a continuum for which transport equations can be formulated. In the Lagrangian formulation, individual droplets are tracked, which leads to a simple formulation but can be challenging in terms of numerics due to the large number of particles to be treated. The comparison of these methods under identical conditions (gaseous flow solver, physical models) is a central aspect of the present work. The most important phenomena that are studied in view of the final application are evaporation and the problem of transverse liquid jets in a gaseous crossflow as a simplified representation of a multipoint system. The final application case is the configuration of a single aeronautical injector mounted in an experimental test bench. It allows to simultaneously apply all preliminary developments. The flow considered is non-reactive but otherwise corresponds to a partial load regime in an aeroengine Due to the pre-heated conditions, the spray issued by the multi-point injection undergoes evaporation. This flow is simulated using Eulerian and Lagrangian methods and the results are compared to experimental data.