Maximizing the turbine entry temperature (TET) is fundamental to increase engine efficiency and reducing fuel consumption. Nonetheless, safety and reliability requirements have to be fulfilled. The life of gas turbine blades is strictly connected to their temperature through the creep deformation process. For this reason temperature monitoring is an essential requirement. Commonly this is achieved by means of devices such as thermocouples which are placed in the bulk flow. The usefulness of these devices as the means of supplying turbine blade temperature information is limited given their slow response time and the fact that the blade temperature is inferred from that of the surrounding gas rather than measured directly. This in turn means that critical blades parts (e.g., trailing edge) or the presence of hot spots are not identified in a discrete manner. These drawbacks can be addressed by using instead a radiation pyrometer, which is characterized by a fast response time, high accuracy, and by being contactless. The pyrometer optical front-end is a lens which collects the radiation emitted by a spot on the turbine blades. However, since the lens is exposed to the harsh engine environment, contaminants entrapped by the turbine flow can therefore be easily deposited on the lens thus filtering the radiation and resulting in an under-estimation of the actual blade temperature. The fouling of the lens is generally tackled by using a purge air system that employs air bled from the compressor to divert those particles whose trajectory is directed towards the lens. Currently the employment of optical pyrometry is often confined to military applications due to the fact that their turbine entry temperatures are higher than in civil applications. Besides, the maintenance schedule established for military engines is far more frequent than what is practiced in airline engines. Therefore, the design of current purge air systems reflects these facts. Before optical pyrometers can be commonly used for civil applications more research is required since some of the fundamentals of the fouling mechanisms remain to be clarified. This is then the knowledge gap the present research sought to fill. Its aim was to conduct a comprehensive investigation of the phenomena that underpins the lens fouling process in order to provide a set of guidelines for optimising the design of purge air systems. The initial part of the research was dedicated to the study of the purge flow inside a given pyrometer configuration. The scope was to identify the main flow structure that determines the fouling process and at the same time to validate the results obtained via computational fluid dynamics (CFD) analyses conducted in a second phase of the research. Given the reduced dimensions of the pyrometer purge system, it was not possible to gain the appropriate optical access to take flow measurements. Consequently, a large scaled experiment was performed, employing the Particle Image Velocimetry (PIV) technique for the acquisition of experimental data of the flow field. The distortion of the image and light reflection introduced by the presence of curved glass surfaces was investigated by means of a feasibility experiment. The experimental study highlighted the presence of a large recirculation zone that can trap contaminants and direct them towards the pyrometer lens. The experimental data were in agreement with computational fluid dynamics results obtained by using two different turbulence models. In a second instance, attention was focused on the particle deposition as seen from a fluid dynamics perspective. A computational fluid dynamics analysis aimed at reproducing the flow field of an existing pyrometer purge system enabled the identification of those features that can significantly impact on the lens fouling process. It was found that the geometry of the air curtain configuration plays a fundamental role. However, given the high speeds involved, the main force governing the contaminants deposition is the drag. Additionally, particles with high inertia hit the purge tube wall and then bounce towards the pyrometer lens, while contaminants with low inertia can be trapped by a large recirculation zone and subsequently directed towards the lens. In a third phase of the research, the impacts between the contaminant particles and the lens were investigated through a finite element analysis (FEA) aimed at identifying the most important factors that contribute to the lens fouling process. Particles moving at low speed can be deposited on the lens by means of electrostatic and Van der Waals forces. Conversely, particles with very high velocity can be deposited on the lens through the same mechanisms involved in the cold spraying process, which is a technique commonly used for coating deposition. A local melting can occur at the interface between the lens and the contaminants due to the high stresses created by the asperities and high sliding velocity of the particles. As a result, while large particles bounce back, debris remains bonded to the lens surface. Last but not least, the findings of the several steps of the present research have been brought together in order to produce guidelines to be followed by engineers engaged in the redesign of more efficient pyrometer purge systems.

This thesis is focused on understanding the flow features associated with a Switched Vortex Valve (SVV) using Computational Fluid Dynamics (CFD) methods for application in aero-engines. In this research the major emphasis was put on detailed flow analysis which was limited in experimental studies of SVVs. Considering the complex geometry of the SVV, for simplicity it was decided to divide the SVV device into two parts before studying the device as whole. These parts are the vortex chamber and flow switching device, which together constitute the SVV device. In this research, different turbulence models were evaluated which are mainly Reynolds average Navier-Stokes (RANS) and unsteady Reynolds average NavierStokes (URANS). The different turbulence models are the k- , SA and the RSM, and for a test case LES was also implemented.

Unlike conventional rigid-link robots, continuum robot, also known as elephant trunk and snake arm robot, has numerous numbers of degrees of freedom, which enables it to be used for accessing confined places in many fields, e.g. minimally invasive surgery, and safe robot/objective interactions, e.g. rapid handling. Up to now, most of the researches are driven to develop two kinds of continuum robots, i.e. flexible and rigid backbones, which can be structured with either small diameter but short length or long length but large diameter. Further, according to the observation of this work, the conventional flexible backbone has a twisting problem when bending in the horizontal plane with end load, rendering a poor position control. Therefore, designing a ‘slender’ continuum robot enabling to be employed in in-situ repair of gas turbine engine is still a challenge, since it requires a long length, small diameter, appropriate flexibility and variable stiffness simultaneously. In the research of this PhD thesis, two unique concepts of continuum robot designs were proposed, i.e. double- and twin-pivot compliant joint constructions. By employing compliant joints, the continuum robot was enabled to be built with small diameter/length ratio, appropriate flexibility, stiffness, and minimised twisting angle. Further, a variable stiffness system was developed in this research, which allows the robot arm able to be articulated in a relatively low stiffness state and dramatically enhance its stiffness in a relatively high stiffness state. With these features, this system was able to be navigated into gas turbine engine (Rolls-Royce Trent XWB) and activate inspection and in-situ repair tasks. Since the new continuum robot concepts were introduced, the fundamental modelling was developed for both design and control of the new structures. Firstly, position kinematics models were developed: one for double-pivot construction deployed a new derivation approach, which can simplify the procedure; the other for twin-pivot construction employed a two-sub bending plane model, due to unique construction of the robot, which is different to the conventional method. Secondly, the actuation force analysis was derived, enabling to calculate the action force of an arbitrary section in a multiple-section continuum robot with any bending angle. Further, buckling failure is a major obstacle for designing the compliant joints, since flexible structure can experience buckling. Hence, the analysis of compliant joint critical buckling load was introduced for guiding the hardware design. Also, a general approach for deriving Jacobian and stiffness matrix of continuum robot was presented in this work. According to the concept and modelling of the new concepts, four demonstrators of continuum robots were built and tested. Comparing with the conventional concept, the double-pivot and twin-pivot concept can decrease the twisting angle by 67% and 98.6%, respectively. Further, in the machining trails, it has been proven that a three-section twin-pivot backbone continuum robot can provide an appropriate stiffness, control accuracy (± 1mm error for sweeping in any ± 5º area in the work volume) and repeatability (± 0.5 mm error in the whole work volume), enabling the system to blend metal materials, e.g. aluminium and titanium, which are the materials widely employed in aerospace industry. Next, a two-section variable stiffness system was tested on this demonstrator and the TCP displacement caused by end load can be decreased by up to 69%. Finally, accessing in gas turbine engines has been realised by the final full length continuum robot (1266mm). It has been proven that the system has an appropriate control accuracy to be navigated to reach the first stage of LPC (low pressure compressor) of a gas turbine engine (Rolls-Royce XWB) by following a pre-planned path. Therefore, it can be concluded that the study of this PhD thesis provides a unique continuum robot design concept, which can be utilised for in-situ repair of gas turbine engine.

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This thesis presents the results from a set of numerical experiments of two-dimensional gas temperature imaging using laser absorption spectroscopy inside a turbofan engine. This measurement environment is characterised by temperatures of 2000 K, pressures of 45 bar, and extremely limited access for the installation of measurement hardware, which renders invasive measurement (thermocouple arrays) or direct imaging (PLIF or pyrometry) methods unviable. An alternative approach is indirect imaging of the temperature, whereby the transmittance of a near-infrared laser light through the gas is measured and used to make inferences about the properties of the gas along the beam; specifically, its temperature, pressure, and molecular constitution. The frequency of the light is chosen to interrogate particular molecular transitions of a target species—water—in such a way that the fraction of light measured at the detector depends on the temperature of the gas through which it has passed. This is an established measurement technique known as tuneable diode laser absorption spectroscopy (TDLAS), but it is possible to extend this method to two dimensions if the transmittance measurements are made over set of coplanar beams that transect the measurement region. Using the principles of tomographic inversion, it becomes possible to image not only the two-dimensional temperature distribution within a gas, but also the pressure and molecular species concentration distributions. In this thesis, extensive numerical simulations are used to critically evaluate this approach when applied to the particular case of the turbine engine, and a new methodology is developed for use in this environment which opens up—for the first time, to the best of the author’s knowledge—the possibility of tomographic reconstruction of a gas pressure. This is challenging because the gas pressure has a strong influence on not only the width of absorption lines, but of their positions on the spectrum, with each line being affected in a different way. To overcome and eventually exploit this dependence, a robust approach which the author terms the spectral fitting approach is developed and tested against the two main existing methods found in the literature: integrated absorbance and peak absorption reconstructions. The spectral fitting approach was found to outperform both methods not only in the high-pressure regime, but throughout the tested pressure range (1-70 bar).The numerical tests were also applied to more realistic measurement environments, including annular measurement regions (modelling the opaque central driveshaft of a turbine engine) with non-uniform molecular species concentrations and gas pressures. In these investigations, the temperature was reconstructed with a relative root-mean-squared error of 2.47%. This demonstrates the theoretical feasibility of tomographic reconstructions of gas temperature in the turbine environment. Numerical optimisation of the methodology is also addressed. The geometric arrangement of beams through the measurement region is investigated with a view to maximise the quality of the reconstructed image, and a new design rule is analytically derived and then applied to generate a set of viable beam arrangements that perform competitively when compared to more conventional regular arrangements. The selection of laser frequencies is also optimised in the specific case of high-pressure spectroscopy, and two near-infrared transitions are suggested as a possible candidate pair for experimental verification.

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