The research presented in this thesis is concerned with the development of numerical techniques and mathematical models for non-Newtonian uids and two-phase ows in pipes and channels. Single phase, turbulent ow calculations of non-Newtonian uids were performed initially. Based on the literature a revised approach to wall modelling is proposed and implemented. The approach uses analytical and experimental analyses of the turbulent boundary layer structure. A comparison with the standard approach is presented. The interaction between turbulence and non-Newtonian behaviour is studied by examining the rate of strain induced by uctuating components of velocity. The statistical analysis of published DNS data is performed. Finally, a model is proposed where the turbulent rate of strain is determined from turbulence quantities used by the Reynolds-averaged Navier{Stokes model and used in the calculation of molecular viscosity. For two-phase ow, the solution procedure using periodic boundary conditions was developed under an assumption of a at interface. The numerical technique was veri ed by comparing to an analytical result obtained for laminar ow in a channel. An extension to three dimensional ow is performed. With periodic boundary conditions standard turbulence models are applied to two-phase strati ed ow. Several models and their corrections for twophase ow are assessed and a new model is proposed. The numerical studies were carried out primiarily in the open-source code OpenFOAM, but initial attempts were made in commercial packages such as STAR-CD and FLUENT. Experimental data collected from the literature are used to verify the results showing good agreement in pressure drops and phase fractions.

Gas path fault isolation is one of the key techniques in Engine Health Management systems. In order to accomplish gas path fault isolation successfully for a gas turbine engine, both an accurate off-design performance model and an effective fault isolation approach are necessary. In this thesis, two original and useful contributions to knowledge are presented: a new gas turbine off-design performance model adaptation approach and a new gas turbine fault isolation approach. This new adaptation approach uses optimal multiple scaling factors obtained by using a Genetic Algorithm to scale inaccurate component characteristic maps in gas turbine performance models to improve their prediction accuracy in different off-design conditions. The major feature of this approach is that it provides non- linear map scaling and therefore is able to provide more effective adaptation. The new fault isolation approach can be used to discover knowledge hidden in engine fault samples, transfers that knowledge into rules, and then uses those rules for fault isolation. In addition, it is also capable of selecting appropriate measurements for fault isolation, dealing with uncertainty caused by measurement noise. Enhanced fault signatures, which are represented by the measurement deviations and their ranking pattern in terms of magnitude, are developed to make gas turbine faults easier to distinguish and hence make this fault isolation approach more effective. The new adaptation approach was applied to the off-design performance model adaptation of a gas turbine, while the new fault isolation approach was employed for fault isolation in a gas turbine. The results show that the new adaptation approach is very effective in improving the prediction accuracy of off- design performance models and the new fault isolation approach is not only effective in fault isolation but also in selecting measurements for isolation and generating fault isolation rules.

This thesis concerns the numerical simulation of dilute macromolecular solutions. Present work details the development of a novel mesoscale simulation method. The developed modeling approach is capable to describe both the macroscopic flow field of the carrier liquid and the micromechanical behaviour of the transported large molecules. In this modeling method, the concept of micromechanical structures is introduced in order to represent macromolecules. The motion of the considered mechanical structures is governed by forces arising from the motion of the bulk fluid phase and microscopic forces arising from stochastic Brownian motion of the solvent molecules. This document presents the motivation, the objectives and systematic steps of the model development. The work presents detailed discussion, verification and validation of the developed modeling method.

Gas turbine sub-idle performance modelling is still in an early development stage and this research aims to provide and improve present techniques, for modelling of windmilling and transient windmilling relights, through to groundstart simulations. Engine ATF data was studied and used to align models created within this research for low and high bypass engines, and compare these models simulation results. Methods for the extrapolation of component characteristics are improved and performed in linearised parameter form, and the most efficient approach discussed. The mixer behaviour is analysed and recommendations of off-design mixer behaviour representation in a sub-idle model are proposed and performed within the modelling. Combustion at sub-idle conditions is investigated with regards to the loading parameter definition, and also its representation for the influence of evaporation rate being limiting to overall combustion efficiency. A method is proposed on extrapolating and representation of the combustion characteristic. Compressor behaviour and the blade torques at locked rotor and windmilling conditions are studied using 3D CFD, producing insight and discussion on CFD suitability and what it can offer at these operating conditions. From the CFD studies generic loss coefficients were created for all compressor blades, from which a zero speed is created for the whole compressor, from a theoretical stage stacking calculation. This zero-speed curve is shown to allow interpolation of component characteristics to the sub-idle region, improving the definition and a predictive approach. A windmilling conditions cascade test rig is proposed, designed and built for validating the CFD loss coefficients. The findings and discussions within this thesis provide useful reference material on this complicated and little documented area of research. The modelling and methods proposed, provide great advancement of the research area, along with further integration of the Cranfield UTC in performance with Rolls-Royce.

This thesis is devoted to understanding and modeling multimaterial interactions, and to develop accordingly a robust scheme taking into account the largest variety of those, with a particular interest in resolving solid/fluid configurations. This very general frame of studies can be tackled with numerous different approaches as several issues arise and need to be addressed before attempting any modelisation of these problems. A first questioning should be the frame of reference to be used for the materials considered. Eulerian shock-capturing schemes have advantages for modeling problems involving complex non-linear wave structures and large deformations. If originally reserved mostly to fluids components, recent work has focused on extending Eulerian schemes to other media such as solid dynamics, as long as the set of equations employed is written under a hyperbolic system of conservation laws. Another matter of interest when dealing with multiple immiscible materials it the necessity to include some means of tracking material boundaries within a numerical scheme. Interface tracking methods based on the use of level set functions are an attractive alternative for problems with sliding interfaces since it allows discontinuous velocity profiles at the material boundaries whilst employing fixed grids. However, its intrinsic lack of variables conservation needs to be circumvented by applying an appropriate fix near the interface, where cells might comprise multiple components. Another requirement is the ability to correctly predict the physical interaction at the interface between the materials. For that purpose, the Riemann problem corresponding to the interfacial conditions needs to be formulated and solved. This implies in turn the need of appropriate Riemann solvers; if they are largely available when the materials are identical (i.e. governed by the same set of equations), a specific Riemann solver will be developed to account for fluid/solid interaction. Eventually, these newly developed methods will be tested on a wide range of different multimaterial problems, involving several materials undergoing large deformations. The materials used, whether modelling fluid/fluid or solid/fluid interactions, will be tested using various initial conditions from both sides of the interface, to demonstrate the robustness of the solver and its flexibility. These testcases will be carried out in 1D, 2D and 3D frames, and compared to exact solutions or other numerical experiments conducted in previous studies.

Many environmental flows are turbulent flows. Depending on the physical aspects of the wind and the urban topology, turbulence might result into unfavourable or even dangerous conditions for the pedestrians. Turbulence can also play a very important role in the transport of toxic pollutants from accidental or intentional releases. Thus, it is vital to understand its complex characteristics so that its features are accurately predicted when computational methods are used. Real urban environment involving separation and reattachment regions provides an excellent testcase for investigating such complex flows. This thesis is focused on analysing the physics involved in flows around building models pertinent to environmental flows in urban areas and to evaluate the applicability of Implicit Large-Eddy Simulation in simulating the specific type of flows. For this purpose, a number of high resolution schemes in the context of Implicit Large-Eddy Simulation (each representing di erent degrees of spatial discretisation accuracy) was assessed. The evaluation of the schemes involved direct validation against experimental data as well as comparisons with DNS and LES data regarding flows within roughness element arrays in staggered arrangements. Initially, the flow within an uniform height cubical matrix was simulated. Four numerical schemes were tested in three di erent grid resolutions. The results were found in very good agreement with the Laser Doppler Anemometry data and they even exhibit DNS-like characteristics in specific locations of comparisons. Thus, it was concluded that high order spatial discretisation schemes allow the accurate representation of reality even in relatively coarse computational meshes. The second case under investigation involved flows within a more realistic representation of urban topology. Results obtained within an array of sixteen elements with five di erent heights reveal that although the roughness of the area is increased, the wind’s velocity profile above the obstacles shares almost the same slope as in the case of the array of the four cubical element. It is believed that this thesis has expanded the range of applications in the context of Implicit Large Eddy Simulation using high resolution schemes and contributed in persuading the scientific community for its potentials.

Turbomolecular pumps require a motor to drive them at speeds of up to 90,000 rpm. These high-speed motors are typically brushless permanent magnet motors that are specifically designed for the application. Intellectual property rights over the design lock the company into one single supplier. Also low manufacturing volumes make the motor expensive to produce. To stay competitive continuous cost reductions or product improvements are necessary. This can only be achieved by looking at new materials, alternative manufacturing methods and simplified assembly processes. The aim of this project is to replace an existing laminated, high-speed (60,000rpm) motor with a new low-cost design. Special considerations need to be given to the motor design with regards to minimising losses due to the high operating speed and the fact that the motor operates in a vacuum. A machine design employing a simple, 3-tooth segmented stator made from soft magnetic composites (SMC) and using non-overlapping coils, and a `deep' plastic bonded magnet on the rotor is proposed to deliver low rotor losses and low manufacturing costs. Four SMC prototype motors have been built, which have led to the following discoveries: (1) Bulk eddy currents in the SMC material cannot be neglected and need to be taken into account separately as a function of the actual component size and shape. (2) A process is suggested to improve the iron loss calculation in SMC, which is evaluated against the prototypes built. (3) SMC material properties are adversely affected by prototype machining, leading to higher iron losses than initially expected. (4) The segmented SMC design has proven to be commercially very attractive. During testing a large sensitivity of the magnetically supported pump shaft to the inherent unbalanced magnetic pull (UMP) force of the 3-tooth, 2-pole design was discovered. This led to a practical and theoretical study into the effects of UMP in this application. An alternative design that avoided the inherent UMP was required, and a 6- tooth, 4-pole motor has been designed and built. For reasons of minimising risks laminations were chosen as the stator material rather than SMC. Test results of this motor in the pump have been successful and the motor has been selected to go into the next generation of turbomolecular pumps.

Today, it is widely recognized that Computational Fluid Dynamics (CFD) methodologies should be used for the analysis of Engineering systems and that design and method of simulation must be practical and realistic to provide cost effective solutions. The recent development in CFD of Engineering Structures has led to the adoption of the Eulerian and Lagrangian concepts of numerical analysis. Although the importance of these concepts cannot be overemphasised in offshore structures hydrodynamics, thus the choice of a concept to define the flow field surrounding a structure is one of the fundamental problems identifiable with marine hydrodynamics, especially where non linear effects become paramount. A narrow focus and use of a concept not adaptable to the ship hydrodynamic problem cannot guarantee the development of a good CFD code. Traditional approaches using the Eulerian and Lagrangian concepts have progressed relatively in the last three decades with the continuous rise in computer development. Smooth Particle Hydrodynamics (SPH), Volume of Fluid Method (VOF), Boundary Integral Method are but a few methods that have been widely used in recent applications. However when a detailed description, evaluation and analysis of the flow field is required in a ship hydrodynamics problem, some of these methods fall short of expectation when they have to strictly adhere to some given assumptions to make the computational analysis stable and provide results. In the use of Eulerian and Lagrangian concepts in fluid dynamics, mathematical skill is an essential requirement for solving flow problems. Modeling methods require discretization of the flow field equations which can be linear and non linear, depending on the parameters for simulation. The understanding of mathematical principles such as Partial differential equations, Fourier transforms and integrals, Integral calculus, Complex Analysis, Matrices, Vectors, Greens Function, Bessel Function, etc are necessary for solving the various equations of fluid motion when calculating the properties of the flow field associated with the hydrodynamic problem. Solution techniques which have the attributes of providing stability, consistency, convergence and accuracy are part of the mathematical requirements for a valid algorithm. Moving Particle Semi - Implicit Method is a computational method for incompressible fluid flow problems. MPS is a lagrangian particle method with robust capability for numerical representation. Particle interaction models representing differential operators in the Navier Stokes equation are proposed for divergence, gradient and laplacian. Boundary interfaces are transformed to interactions between particles. Computational difficulties associated with Eulerian methods such as numerical diffusion and regriding due to fragmentation and large deformations can be overcome with MPS method. This study addresses in detail the MPS method as a computational tool for wave - structure interactions. Investigation of both laboratory and numerical experiments associated with Wave - Structure Interactions were the primary focus of this study with the Development of a 2-dimensional MPS Simulation and Analysis of Wedge Water entries code, and Green Water flow simulation and effects on FPSO deck structure. Computational codes were developed for the prediction of deck flow and wave loads on the deck structure using the Navier Stokes equations. An experimental study was carried out at the Newcastle University Marine Laboratory in order to understand the detailed nature of green sea physics. Green Sea effects were measured on a model FPSO. Empirical relations and data obtained from the experiment were used in the numerical prediction code to obtain the deck flow pattern and validate the wave loads on the deck structure using the MPS method. The experiment on merit was necessary to test the capability of the hydrodynamics facility and provide understanding of the underlying principles surrounding the green water phenomena.

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