Large Eddy Simulation (LES) are performed for premixed gas phase turbulent deflagrations in confinements with particular modeling emphasis to capture proper flame behaviour i.e. quenching and acceleration near the obstacles/solid surfaces. Flamelet based Coherent Flame Model (CFM) is adopted for simulating turbulent flame deflagration. Conservation equation for Flame Surface Density (FSD) is considered to account for the non-equilibrium transport of FSD. Modeling improvements in terms of flow-wall and flame-wall interactions are implemented in the governing equations of CFM, which serve as wall boundary closures for numerical combustion simulations with wall interactions. The enthalpy loss factor considering the non-isobaric condition is used in the present study to accurately capture the region where flame is affected by the presence of wall. Model constants for the flame-wall interaction are determined in a posteriori test. The CFM solver along with flow and flame-wall interactions is been developed in OpenFOAM framework. The solver has been first validated for a non-reacting channel flow simulations with the DNS data. Validation study for the flow-wall interaction is performed by considering the periodic hill configuration in a channel. DNS of a ‘V’-flame in a channel flow is used as posteriori test to fix the flame-wall model constants. The numerical predictions of the CFM solver with wall interactions are assessed by simulating the turbulent flame deflagrations in a quench mesh, repeated obstructed channel and in a model hydrogen storage facility. Numerical results establish that the wall interaction models have improved the predictions and are able to account for change in characteristics of the turbulent premixed flame and turbulence length scales in the near-wall region.

In aircraft, the main landing gear wheels skid on the runway at the moment of touchdown because of high slip. A slipping tyre generates enough heat to melt its rubber. Melted rubber is easily eroded by the friction force between the tyre and runway; and part of eroded rubber stays on the runway, and other is burnt off as smoke. Since the early days of airplane use, a number of ideas have been patented to improve tyre safety and decrease the substantial wear and smoke during every landing by spinning the gear wheels before touchdown. In this thesis, there are three parts of research work. First part is to find the effectiveness of the technique of pre-spinning the wheel to reduce the tyre tread heat and wear, and then choosing the initial wheel rotation speed that prevent the tread rubber from melting temperature. For achieving this, a coupled structural – thermal transient analysis in ANSYS has been used to model a single wheel main landing gear as a mass-spring system. This model has been chosen to analyze the wheel's dynamic behaviour and tyre tread temperature and wear during the short period from static to a matching free-rolling velocity in which the wheel is forced to accelerate by the friction between the tyre and ground. The tyre contact surface temperature and wear have been calculated for both the initially static and pre-spun wheels in order to compare the temperature and wear levels for different initial rotation speeds. In the second part, the required torque to spin the aircraft wheel to the required angular speed at approach speed has been calculated using ANSYS CFX, which is used to determine the wheel aerodynamic forces developed by simulation of fluid flows in a virtual environment. In the last part, several types of wind turbines have been simulated.

The research reported in this thesis has examined means of enhancing the performance of the Optimal Trade-off Maximum Average Correlation Height (OT-MACH) filter for target detection in Forward Looking Infra-Red (FLIR) imagery acquired from a helicopter and border security FLIR camera in northern Kuwait. The data acquired with these FLIR sensors allows real-world evaluation of the comparative performance of the various filters that have been developed in the thesis. The results obtained have been quantified using well known performance measures such as Peak to Side-lobe Ratio (PSR) and Total Detection Error (TDE). The initial focus was to study the effect of modifying the OT-MACH parameters on the correlation metrics. A new optimisation technique has been presented, which computes statistically the filter alpha parameter associated with controlling the response of the filter to clutter noise. A further modification of the OT-MACH filter performance using the Difference of Gaussian bandpass filter (named the D-MACH filter) as a pre-processing stage has been described. The D-MACH has been applied to several test images containing single and multiple targets in the scene. Enhanced performance of the modified filter is demonstrated with improved metrics being obtained with less false side peaks in the correlation plane, especially when multiple targets are present in the test images. A further pre-processing technique was investigated using the Rayleigh distribution as a pre-processing filter (named the R-MACH filter). The R-MACH filter has been applied to multiple target types with tests conducted across various image data sets. The filter demonstrated an improvement over the Difference of Gaussian filter in terms of 6 reducing the number of parameters needing to be tuned whilst producing further enhanced correlation plane metrics. Finally, recommendations for future work has been made to improve the use of the OT-MACH filter in target detection and identification. A novel training image representation is proposed for further investigation, which will minimise the computational intensity of using the MACH filter for unconstrained object recognition.

This thesis focuses on the design, development and testing of a two dimensional particle in cell (PIC) code (PICSIE) written in Matlab. The code is applied to the specific problem of modelling the performance of dual stage ion thrusters. The code simulates one full aperture within dual stage ion thruster systems, focusing on the flow of ions through the aperture. Only the ions have been included in the simulation in order to minimize running time. The results produced by the simulation code are compared with results obtained from the vacuum chamber testing of the DS4G prototype, along with results from other simulation codes and research papers in order to verify the performance of the simulation code. The Dual-Stage 4-Grid (DS4G) and Dual-Stage 3-Grid (DS3G) thrusters are both sim- ulated in order to compare the performance of the two thrusters and assess the benefits and disadvantages of including the fourth grid in a dual stage thruster system. Different grid configurations are simulated in order to find the most efficient configuration of the ion optics and accelerating voltages for each thruster, with the aim being to find the con- figurations that produce the maximum particle momentum, thrust and specific impulse while minimizing the rate of erosion of the ion optics and maximising the efficiency of the thruster. These simulations are applied to the problem of deciding if the advantages provided in using a 4th grid outweigh the disadvantages compared to the 3 grid design. The results show that if erosion due to backstreaming ions is disregarded, including the fourth grid in the thruster design results in no apparent advantages in terms of the perfor- mance parameters studied in this work. The only noticeable difference between the three and four grid cases is a significant increase in the change in ion momentum observed when the fourth grid is not included in the design. The conclusion of the work is that the fourth grid should not be included in the dual stage design unless a very long lifetime is required and it is thought that erosion due to backstreaming will prevent the three grid thruster from fulfilling this criteria. The concept of propagating waves through the plasma within the ion thruster discharge chamber is investigated, with the aim of discovering any benefits and improvements in performance that may arise and forming a conclusion on whether further study on the topic of waves within the discharge chamber may be beneficial. No improvements in per- formance parameters were observed in this work, although further study in the area may show benefits to introducing waves into the plasma.

Physics of laminar-to-turbulent transition in a separated-reattached flow subjected to two free-stream turbulence levels have been explored using Large-Eddy Simulation (LES). Separation of the laminar boundary layer occurs at a curvature change over a flat plate with a semi-circular leading edge. A numerical trip has been used to generate the targeted free-stream turbulence levels. A dynamic Sub-grid-scale (SGS) model has been employed and excellent agreement has been achieved between the LES results and the experimental data. Detailed investigation of the LES data has been carried out to explore the primary instability mechanism at low (< 0.2%) and high free-stream turbulence (5.6%). The flow visualisations and spectral analysis of the separated shear layer reveal that the two-dimensional Kelvin-Helmholtz instability mode, well known to occur at low free-stream turbulence levels, is bypassed at a higher level leading to earlier breakdown to turbulence. The whole transition process leading to breakdown to turbulence has been revealed clearly by the flow visualisations and the differences between the low and high free-stream turbulence cases are clearly evident. Coherent structures are also visualised using iso-surfaces of the Q-criterion and for the high free-stream turbulence case the spanwise oriented two-dimensional rolls, which are clearly apparent in the low free-stream turbulence case, are not visible anymore. Detailed quantitative comparisons between the present LES results against experimental data and the previous LES results at low free-stream turbulence using a staggered grid have been done and a good agreement has been obtained, indicating that the current LES using a co-located grid with pressure smoothing can predict transitional flows accurately. Comprehensive spectral analysis of the separated shear layer at two free-stream turbulence levels has been performed. Under very low free-stream turbulence condition, a distinct regular vortex shedding and trace of the low-frequency flapping phenomena were detected. Under the higher free-stream turbulence however, a mild high-frequency activity was observed. No low frequency oscillations could be detected.

The aims of the research work described in this thesis were to use computational fluid dynamics (CFD) to investigate the factors affecting the performance of a multi-stage downdraught evaporative cooling device for low-energy cooling of buildings developed from a novel prototype device described by Erell et al. (2008) and Pearlmutter et al. (2008); and to model and explore the performance of the device when integrated within a hypothetical, but representative, building in a hot dry climate. The research work was carried out with initial objectives of: understanding and modelling water spray evaporation using CFD methods; verifying the CFD model of water spray evaporation using published experimental data; modelling and examining the spray characteristics of the nozzles used in the work by Erell et al. and Pearlmutter et al.; creating a detail model of the prototype multi-stage downdraught evaporative cooling device described by Erell et al. and Pearlmutter et al.; carrying out a series of CFD simulations of the prototype device under wind-driven operation with and without water sprays and comparing the results obtained with available experimental data. Following completion of these initial studies, a detailed investigation of the factors affecting the performance of a multi-stage cooling device derived from the prototype device was carried out. This involved carrying out simulations: to select the most effective wind catcher geometry; to optimize the number and arrangement of water spray nozzles; and to select a range of geometrical parameters. Following completion of these additional studies a model of a two-floor hypothetical building with an integrated multi-stage downdraught evaporative cooling device of optimum geometry and a wind catcher was created, and simulations to investigate the performance under varying wind speeds and environmental conditions were carried out. All simulations were carried out using ANSYS CFX, versions 12.0, or 12.1 or 13.0. The results obtained indicated that comfortable conditions within the cooled space could be achieved over almost all of the range the wind speeds and environmental conditions studied. Some recommendations for future work are given.

This report describes a thesis project in aeronautical engineering carried out during April and May 2011 at ST Aerospace Solutions, Arlanda. The company is one of Europe’s leading aviation component maintenance companies. The task for this thesis project has been to develop a baseline overhaul work package for the thrust reverser system of the Rolls-Royce Trent 700 jet engine. An overhaul work package is a collection of maintenance work sheets (MWS) used by the maintenance organization to confirm that a specific maintenance procedure has been carried out correctly. Documenting the maintenance work performed on a component is required in order to comply with the regulations of the European Aviation Safety Agency (EASA). To be able to solve the task, the authors had to study maintenance manuals, learn the functions of the thrust reverser and get an overview of how the maintenance organization works. Much of the work has been conducted in consultation with the company’s engineering department. The result is an overhaul package consisting of approximately 40 MWS’s. These have been designed to promote traceability of actions and to be easily revisable. / Denna rapport är resultatet av ett examensarbete i flygteknik som genomförts under våren 2011. Arbetet utfördes hos ST Aerospace Solutions, ett av Europas ledande företag för komponentunderhåll inom flygindustrin. Uppgiften har varit att utveckla ett översynspaket för reverseringssystemet på Rolls-Royce jetmotor Trent 700. Ett översynspaket består av en uppsättning dokument, så kallade ”maintenance work sheets” (MWS), som används för att säkerställa att underhållsorganisationen har utfört det underhåll som krävs. Detta är ett krav enligt den Europeiska luftfartsmyndigheten EASA:s Part 145. Metodiken har främst bestått i att sätta sig in i relaterad dokumentation och underhållsmanualer, samt att skapa sig en förståelse för hur reverseringssystemet och underhållsorganisationen är uppbyggda. Större delen av arbetet har utförts på plats för att kunna samarbeta och diskutera med företagets ingenjörs- och verkstadsavdelningar. Slutresultatet är ett översynspaket som innehåller ca 40 MWS:er, vilka behandlar hela underhållsprocessen. Paketet har utformats med god spårbarhet och reviderbarhet i åtanke.

This thesis is concerned with the development of new fibre optic based sensors for liquid level and temperature measurement. For the measurement of fluid level an intrinsic sensor has been developed whereby the fibre itself forms the sensing medium. This fibre is made from a plastic, doped with a dye that fluoresces when illuminated by ultra-violet light. The sensing fibre is continuously illuminated but the fluid around it absorbs the light and hence the fluid level controls the intensity of light generated within the fluorescing fibre. The measurement of temperature forms the bulk of this thesis with liquid crystals being used as the transducing medium. Many different schemes have been investigated and characterised using their thermochromic, light scattering, and electro-optic properties. The latter necessitated the production of miniature photovoltaic devices which, apart from being a novel way of generating quasi-regulated electrical power, provide an alternative approach to energising many other types of hybrid sensor systems that at present are forced to use more complex techniques. Finally a simple theory has been developed to describe the behaviour of the liquid crystal based systems. The theory has been solved numerically and is in good agreement with the experimental results.

Current landing and braking systems are associated with the approach, flare and rollout. Automatic and independent brake systems prevent skidding but do not restore the aircraft to the original trajectory. None use the normal aerodynamic surfaces to augment braking effectiveness to steer the aircraft during sudden changes in runway surface conditions. Many aircraft accidents occur during landing. The task of bringing the aircraft to a safe taxing speed from touchdown in variable weather conditions is the most difficult manoeuvre that a pilot has to make. There is no opportunity to recover or reattempt the manoeuvre. It is the only phase of the aircraft operation that has not been effectively improved through the use of autopilot control systems. Improving this regime of operation through the use of formally redundant aerodynamic control surfaces is the subject of this thesis. This thesis describes the development and testing of a controller, auto-pilot and ABS combination that uses ailerons to control the normal loading differential between the main gear of a B747-100 for the purpose of increasing the directional control so that is it possible to either minimising the centre line off-set or to maintain heading of a landing aircraft. The aileron based differential nonnal loading controller uses the brake line pressure differential as an input variable to control the ailerons during touchdown. During the II maximum braking case, the brake line pressure is proportional to the difference in runway friction coefficient, normal loading, and brake disk stack friction coefficient. Landing aircraft are extremely non-linear in function. To overcome this, a model and Controller that generates the appropriate non-linear mathematical description of the aircraft during the landing phase and generates an effective controller that effectively generates an increase in normal gear force on touch down of 100% and thereby allowing the aircraft to be controlled in direction during hazardous conditions was developed. The outcome of the work is that the use of a control scheme and unconventional use of ailerons can significantly improve aircraft landing characteristics during adverse landing weather conditions and reduce the number of accidents. Current advances in future aircraft design are tending towards tailless aircraft such as Boeing's Blended Wing Body aircraft and a similar study by Airbus. These aircraft do not have sufficient rudder or engine yaw control at landing speeds. This work provides a method of steering the aircraft from touchdown to taxi speed through normal force and brake augmentation.

Strengthening of existing structures has become an important aspect of civil engineering. Various methods exist and have been developed in the last few decades one of which has become increasingly popular- strengthening using fibre reinforced polymers. Their excellent mechanical properties and resistance to different environmental conditions make them a viable alternative to the traditional materials like concrete and steel. In this study the effect of elevated temperatures on the behaviour of FRP strengthened reinforced concrete beams is investigated. The behaviour of reinforced concrete beams strengthened with FRF laminates has been investigated by different researchers in the last two decades. Ultimate load, failure modes and improved techniques for strengthening have been the main areas of interest. As a result of the extensive research several classifications and design guidelines have been proposed to ensure better performance and prevent premature failures of the systems. One important aspect of the strengthening is the susceptibility of polymers to significant and rapid reduction of their strength when exposed to elevated temperatures and fire. Little research has been done up-todate on the residual properties of FRP strengthened systems after heating and cooling. Three experiments have been conducted for the purpose of this study. The bond strength of CFRP strengthened systems is first investigated for temperature range of 20°C to 300°C. The behaviour of small-scale strengthened beams during the heating process is presented next. The third experiment is then designed to determine the residual flexural capacity of the heated and cooled minibeams. The results are presented and compared indicating residual strength of the systems to 30% compared to their performance at room temperature