A dynamic inflow model is a powerful tool for predicting the induced velocity distribution over a rotor disc. On account of its closed form and simplicity, the model is highly practical especially for studying flight mechanics and designing control systems for helicopters. However, scant attention has been so far paid to applying this model to analyse autorotative rotors (i.e. rotors in the windmill-brake state), which differ from powered helicopter rotors (i.e. rotors in the normal working state) in that the geometric relation between the inflow and the rotor disc. The principal aim of this research is to theoretically investigate the applicability of existing dynamic inflow models for autorotative rotors, and if necessary, to provide a new dynamic inflow model for autorotative rotors. The contemporary dynamic inflow modelling is reviewed in detail from first principles in this thesis, and this identifies a modification to the mass-flow parameter for autorotative rotors. A qualitative assessment of this change indicates that it is likely to have a negligible impact on the trim state of rotorcraft in autorotation, but a significant effect on the dynamic inflow models in certain flight conditions. In addition, this thesis includes a discussion about the small wake skew angle assumption, which is invariably used in the derivation of Peters and He model. The mathematical validity of the assumption is cast doubt, despite the resultant model has experimentally been fully validated. The author discusses on a theoretical ground the possible reason why the Peters and He model works well in spite of its inconsistent derivation

The interaction of a vortex with a lifting surface occurs in many aerodynamic systems, and can induce significant airloads and radiate impulsive noise. Yet due to their complex nature, the ability to accurately model the important flow physics and noise radiation characteristics of these interactions in realistic situations has remained elusive. This work examines two cases of vortex-lifting surface interactions by enhancing the capabilities of a high fidelity flow solver. This flow solver utilises high spatial discretisation accuracy with a 5th order accurate WENO scheme, and overset meshes to accurately resolve the formation, evolution and interaction of a tip vortex using an inviscid approximation of the fluid. An existing computational infrastructure is further developed and applied to analyse blade-vortex interactions that occur on a helicopter rotor. An idealised interaction is studied, where an independently generated vortex interacts with a rotor. It is found that through the employment of adequate spatial and temporal resolution, the current methodology is capable of resolving the important details of the interaction over a range of vortex-blade miss distances. A careful study of the spatial and temporal resolution requirements is conducted to ensure that the computed results converge to the correct physical solution. It is also demonstrated that a linear acoustic analysis can accurately predict the acoustic energy propagated from these interactions to the far-field, provided the blade surface pressures are accurately computed. The methodology is then used to study an idealised propeller wake-wing interaction, which occur behind a tractor mounted turboprop. A computationally efficient method of modelling the wake-wing interaction is developed and the computed surface pressures of the interaction are confirmed to agree well with the experimental data. The analysis is coupled to an optimisation algorithm to determine a novel wing design, and it is found that significant drag reductions can be achieved with small changes in the twist distribution of the wing. This work confirms that by using a combination of strategies including efficient grids, high order accurate numerical discretisations and a flexible software infrastructure, high fidelity methods can indeed be used to accurately resolve practical cases of vortex-lifting surface interactions in detail while being feasible in a design setting. The airloads and aeroacoustics from these interactions can be accurately predicted, thus confirming that with the modern advances in computing and algorithms, high fidelity methodologies such as those presented in this thesis are in a position to be used to gain a deep understanding of the relevant flow physics and noise radiation patterns, and their impact on aircraft design.

As a rotorcraft descends or manoeuvres, the interactions which occur between the rotor blades and vortical structures within the rotor wake produce highly impulsive loads on the blades and with these a highly intrusive external noise. Brown’s Vorticity Transport Model has been used to investigate the influence of the fidelity of the local blade aerodynamic model on the quality of the prediction of the high-frequency airloads associated with blade-vortex interactions and thus on the accuracy with which the acoustic signature of the aircraft can be predicted. Aerodynamic, wake structure and acoustic predictions using the Vorticity Transport Model are compared against the HART II wind tunnel data for an experimental rotor based on the characteristics of the Bo105 rotor. The model can resolve very accurately the structure of the wake, and allows significant flexibility in the way that the blade loading can be represented. The predictions of two models for the local blade aerodynamics are compared for all three of the HART II flight cases. The first model is a simple lifting-line model and the second is a somewhat more sophisticated lifting-chord model based on unsteady thin aerofoil theory. The predicted positions of the vortex cores agree with measured data to within a fraction of the blade chord, and the strength of the vortices is preserved to well downstream of the rotor, essentially independently of the resolution of the calculation or the blade model used. A marked improvement in accuracy of the predicted high-frequency airloads and acoustic signature of the HART II rotor is obtained when the lifting-chord model for the blade aerodynamics is used instead of the lifting-line type approach. Errors in the amplitude and phase of the loading peaks are reduced and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake. Predictions of the acoustic signature of the rotor are similarly affected, with the lifting-chord model at the highest resolution producing the best representation of the distribution of sound pressure on the ground plane below the rotor.

The aim of the present thesis is to develop new methods that are useful for a space mission analyst to design low thrust trajectories in the preliminary phases of a mission study, where the focus is more on exploring various concepts than on obtaining one optimal transfer. The tools cover three main axes: generating low thrust trajectories from scratch, improving existing low thrust trajectories and exploring large search spaces related to multiple gravity assist transfers. Stress is put on the computational efficiency of the tools. Transfer arcs are generated with shaped based approaches, which have the advantage of having the ability to reproduce close to optimal transfers satisfying time of flight constraints and varied boundary constraints without the need for propagation. This thesis presents a general framework for the development of shape-based approaches to low-thrust trajectory design. A novel shaping method, based on a three-dimensional description of the trajectory in spherical coordinates, is developed within this general framework. Both the exponential sinusoid and the inverse polynomial shaping are demonstrated to be particular two-dimensional cases of the spherical one. The pseudo-equinoctial shaping is revisited within the new framework, and the nonosculating nature of the pseudo-equinoctial elements is analysed. A two-step approach is introduced to solve the time of flight constraint, related to the design of low-thrust arcs with boundary constraints for both spherical and pseudo-equinoctial shaping. The solutions derived from the shaping approach are improved with a feedback linear-quadratic controller and compared against a direct collocation method based on finite elements in time. Theoretical results are given on the validity of the method and a theorem is derived on the criteria of optimality of the results. The shaping approaches and the combination of shaping and linear-quadratic controller are tested on four case studies: a mission to Mars, a mission to asteroid 1989ML, to comet Tempel-1 and to Neptune. The design of low thrust multiple gravity assist trajectories is tackled by an incremental pruning approach. The incremental pruning of reduced search spaces is performed for decoupled pairs of transfer legs, after which regions of the total search space are identified where all acceptable pairs can be linked together. The gravity assists are not powered therefore the trajectory is purely low thrust and the transfer arcs are modelled by shaping functions and improved with the linear quadratic controller. Such an approach can reduce the computational burden of finding a global optimum. Numerical examples are presented for LTMGA transfers from Earth to asteroid Apollo and to Jupiter.

This thesis presents an initial Finite Element (FE) based modelling investigation aimed at supporting the development of 'smart' tyre or intelligent tyre technologies. Physical tests carried out with a stationary (non-rolling) and rolling experimental tyre are used to enhance understanding of tyre behaviour in the contact patch and validate the modelling methodology. Simulation results with the explicit FE package LS-DYNA are then used to characterise the internal stresses and strains at several positions in the tyre tread. Two separate FE models are developed to simulate the stationary and rolling tyre behaviour at the macroscopic level. The models differ only with respect to the mesh density in the circumferential direction, the mesh through the cross section is identical. The complex tyre structure is represented as a rubber and reinforced rubber composite, and the mesh specification and the material descriptions used in the models are discussed. The structural behaviour of the stationary experimental tyre under normal load is simulated. The inflation of the tyre, the wheel fit and the normal loading against the horizontal surface are represented. Simulation results are also presented when a subsequent longitudinal or lateral load is applied to the stationary tyre. These analyses were conducted to determine the longitudinal and lateral tyre stifffiesses, respectively. The predicted normal load-deflection characteristics and contact patch dimensions (length and width) are compared with a reasonable degree of success to those obtained in the full-scale physical tests. The longitudinal and lateral simulations also appear to give realistic tyre stiffnesses. The contact patch dimensions give a good trend-wise agreement, but the length and width are greater than the experimental measurements. A parametric study is carried out and this disparity is related to a deficiency in the performance of the contact algorithms. It is concluded that it not straightforward to accurately predict contact patch behaviour, and therefore the internal transient stresses and strains in a rolling tyre in absolute terms. However, the good trend-wise agreement suggests that the modelling methodology should be capable of predicting internal transient responses which are related to the 'actual' deformations in the contact region. To simulate the rolling tyre behaviour on flat bed and drum surfaces, consideration is given to the inflation of the tyre, the wheel fit, the normal loading and the rotation of the tyre. Numerical instabilities are found to occur and these are related to imperfections inherent in version 950d of the code. This version was, at the time, the most up to date release. The current release is version 960 and it does not contain many of the imperfections in the earlier version. Thus, the flat bed simulation is repeated using the current version. The predicted contact patch stresses are presented and a reasonable correlation is achieved with the experimental data. The internal stresses and strains are then characterised at a number of selected positions in the tread region. These stresses and strains are discussed in context with the development of smart tyre technologies and are useful as a guide to the most appropriate location for an in-tyre sensor (or sensors).

The noise generated by aircraft can be easily heard by those living under the flight path of passenger or cargo carriers. It is considered an environmental pollutant and is treated as such by the International Civil Aviation Organization (ICAO) who monitor and review noise levels. The ICAO imposes substantial fines on those carriers who do not adhere to the decibel limitations. With the new limit or `stage' enforced in 2006, aircraft manufacturers (including jet engine manufacturers) are seeking ways to reduce the noise created by an aircraft. A 1/150th scale model, based on the exit geometry typically found on commercial jet engines, was designed and manufactured at Warwick. The laboratory jet flow conditions operated at 0.7 Mach. The work presented in this thesis looks at the noise generated in a subsonic, co- owing jet, with particular focus given to the distribution sound sources from 5 kHz to 80 kHz (0.375 St to 6.0 St). An acoustic mirror mounted on a motorized 3-way traverse measured radiated sound in the co-flowing jet to produce 2D sound source maps. This is done using combinations of smooth cowl and chevrons for the core and bypass nozzles. For frequencies less than 30 kHz, a reduction of noise was observed using the bypass chevron nozzle compared with the bypass smooth cowl nozzle. Laser Doppler Anemometry (LDA) was used to reveal the 2D flow dynamics of the jet, supporting the acoustic distribution results with velocity profiles of the flow. The change in the flow dynamics with different nozzle combinations is discussed and different regions of the flow were identified.

The control of the noise and vibration generated by an automobile is referred to as Noise, Vibration and Harshness (NVH) engineering. It involves identifying the design detail required to reduce the noise and vibration inside the passenger compartment of the vehicle to levels that are acceptable to the customer. It also involves delivering an engine or a powertrain sound character that is both pleasing to the customer and that suits the character of the vehicle. Tuning the sound generated by a vehicle to deliver a particular character is referred to as Sound Quality Engineering. This document summarizes the work of the EngD research programme that was aimed at developing a structured process for engineering the Powertrain Sound Quality of an automobile. The need for developing a Sound Quality Engineering Process at Jaguar Cars was identified through a review of customer evaluations of the sound in Jaguar's vehicles and those of its competitors. This review established that Jaguar's existing vehicles were trailing the leading competition in terms of the delivery of Powertrain Sound Quality. The reason for this shortfall was that the NVH Department at Jaguar did not have a focus on delivering the customer requirements. Without this focus there was no means of using the customer level requirements, for Sound Quality to drive the vehicle design process. The EngD research programme resulted in the formulation and implementation of a Sound Quality Engineering Process at Jaguar Cars that addressed this need. The first part of the research programme involved developing a means of quantifying the differences in the subjective Sound Quality character perceived by the customer. It was established that the subjective nature of the Powertrain Sound Quality could be represented by two underlying dimensions; a measure of the degree of Refinement and a measure of degree of Powerfulness. An assessment technique was developed that enabled the subjective Sound Quality character for a given vehicle to be quantified through its location within a 2-Dimensional Sound Quality Space, the axes of which were defined by each of the two underlying dimensions of Sound Quality. This 2- Dimensional Sound Quality Space provided the means of quantifying the differences in the Sound Quality characters for all of the vehicles competing in the luxury vehicle sectors. It was applied to define subjective Sound Quality targets for all of the new vehicle programmes at Jaguar Cars. These targets identified the required improvements to each of the two underlying dimensions of Sound Quality needed to address the shortfalls in Jaguar Cars' existing vehicles. The second part of the research programme involved identifying the key acoustic features within the sound signatures of Jaguar's vehicles that were responsible for determining the differences in subjective perception between these vehicles and their competitors. The changes to these key acoustic features were related to the required improvements to each of the two dimensions of Sound Quality that were established from the subjective target setting process. The final part of the research programme involved developing techniques that linked these key acoustic features to the noise sources and paths that were responsible for generating them. Through this link it was possible to establish the changes to these noise sources and paths that were necessary to deliver the required changes to the key acoustic features. In this way the required improvements to each of the two underlying dimensions of Sound Quality were used to define the vehicle design specification at the concept stage of the vehicle development programme and consequently drive the vehicle design process. The ability to link the subjective customer level requirements for Sound Quality to the design detail specification has overcome the previously identified shortfall within the NVH development process at Jaguar Cars. The techniques developed during the EngD research programme were formulated into a Sound Quality Engineering Process. Although the process was developed for Jaguar Cars the findings from the research and the techniques developed have since been applied by the different brands within the Ford Motor Company. Within Jaguar Cars the process has been implemented across all of the new vehicle programmes. It has directly resulted in significantly improved Sound Quality characters in the new vehicles that have been recently introduced to the luxury vehicle market.

With the increasing adoption and usage of hybrid electric vehicle (HEV) technologies, there is a growing recognition that attributes such as dynamics, driveability and refinement can have an adverse affect on customer acceptance. There are a number of new challenges associated with their refinement, in particular their sound quality. These issues include: understanding customers’ perceptions of new sound sources, such as electric motor/generators (M/G) and electronic switching devices; reduced masking from the internal combustion engine (ICE); the effect that a more advanced control strategy can have on vehicle-level sound (both internally and externally); and the effect of new sound character on customer perception. Given these new challenges for the sound quality of HEVs, the best approach for learning about perceptions needed to be determined. Interactive noise, vibration and harshness (NVH) simulation is well suited to further our understanding of these issues. The process for developing models for interactive NVH simulation of conventional vehicles is well established. However, research was necessary to both enhance this process for the creation of HEV models and to create new assessment methods. This report gives a brief overview of a project to deliver this. The key stages were: classification of unique HEV operations; development of a HEV NVH model; validation of the NVH model to determine its suitability for interactive simulation; leading onto recommendations for the use of new HEV sound quality models for assessment. An interactive HEV model has been successfully created and used in a number of newly created HEV sound quality evaluations. Three assessments were created and carried out which addressed new HEV related refinement issues of varying ICE masking, varying control strategy and the effect of added interior synthesized sound on customer perception. Key findings included: preference for reduced internal combustion engine (ICE) sound in the Toyota Prius and significant differences in perception of the same HEV, over the same drive cycle with varying initial battery state-of-charge (SoC). The process developed and carried out and learning achieved has been documented as a selection of flowcharts and can be used by OEMs or sound specialists as a means for improving HEV sound quality.

The first approach utilises a thin film of acrylic that is moulded onto the outside of a polycarbonate substrate. It was found that the gate of the injection mould cavity must be of uniform cross section otherwise local shear heating can occur and melt the acrylic film. The injection gate must also be located entirely on one side of the mould cavity otherwise the film is punctured by the molten polycarbonate and free to float within the cavity. Any mixing of the two materials will lead to opaque components due the difference in the refractive indices. The film was found to improve the UV resistance of any component, acting as a protective buffer for the polycarbonate. A new variety of hardcoat was applied to film-backed samples to impart abrasion resistance and samples were found to outperform commercially available alternatives under recognised laboratory conditions. The film-backed samples also exhibited excellent impact resistance when impacted upon the film-face. However, similar components failed at extremely low energy levels when impacted from the non-film face because flaws in the acrylic film caused cracks to be initiated when the film was placed into tension. The level of adhesion between the film and the polycarbonate has been found to be critical and if the failure mechanism could be guaranteed, then intruder resistant glazing that could be broken from the inside in an emergency becomes a possibility. Such a product would address the identified consumer concern of being trapped in a vehicle. The second approach utilises simultaneous dual injection moulding (2K), which has previously only been used to manufacture coloured components. A successful feasibility study was undertaken to demonstrate the concept of producing transparent components via such a process. This showed that much greater control is required for transparent applications otherwise the skin and core materials mix and opaque components are produced. The generally accepted academic principles associated with the process have been shown to be too simplistic and cannot be relied upon to guarantee good results. The ratio of viscosities of the skin and core materials appear to be more dominant than previously thought and the relative injection speeds of the two materials has a direct influence upon interfacial mixing and haze generation. It was also found that haze could be avoided if the refractive indices of the skin and core material were matched to within ±0.002, but this is impractical. A third area of research examined the feasibility of introducing structured glass fibres weaves into transparent components to improve rigidity. The study resulted in the construction of a transparent glass fibre pre-preg that could be moulded onto the outer surface of polycarbonate components. Flexural tests revealed that a single layer of glass fibre increased the flexural modulus of test samples by a factor of 3, whilst transparency and clarity were retained. Two patents have been filed as a direct result of this work.

Environmental and commercial pressures have forced the aerospace industry to look at alternatives to riveting for the manufacture of aluminium aircraft structures. This resulted, at the end of last century, in an extensive study by Airbus into the possiblities of using CO2 lasers, which led to the process being implemented for a (small) number of stringer-to-skin fuselage panels in the newer Airbus models. Since this initial commercial success, new laser sources have become available that are more suitable for the welding of aluminium than CO2 lasers, in the form of Nd: YAG and Yb-fibre lasers. Both produce a wavelength that is absorbed more efficiently by aluminium alloys than the CO2 laser wavelength, resulting in an improved keyhole stability, as demonstrated in the late nineties for Nd: YAG lasers. In addition, Yb-fibre lasers have become available at output powers higher than available for Nd: YAG lasers, allowing thicker sections of aluminium to be welded in a single pass. However, despite their claimed advantages, no efforts were made to demonstrate the potential of these lasers for (aluminium) aircraft manufacture. For this reason, the author initiated a series of studies in 2001, with the overall aim to develop procedures to laser weld both thin (3.2mm) and thicksection (12.7mm) aerospace aluminium alloys using these fibre-delivered lasers to a weld quality, in particular related to weld metal porosity, suitable for aerospace service. The focus in this research was on weld metal porosity, because this is a particular problem when laser welding aluminium, either in the form of fine (hydrogen) porosity or larger porosity associated with an unstable keyhole behaviour. The benchmark weld metal porosity for this study was obtained from the stringent weld quality classes defined in BS EN 13919-2 and AWS D17.1. The approach to this research was in three parts, with work in the first aimed at demonstrating that a 3kW Nd: YAG laser was capable of producing low-porosity welds in 3.2mm thickness 2024 aluminium alloy, and thus can be considered for replacing the CO2 laser currently used for the stringer-to-skin fuselage application. Prior to the final part of the research, in which a 7kW Yb-fibre laser was used to demonstrate that these benchmark porosity levels could also be achieved in thicker section (aerospace-grade) aluminium, a comparison study was carried out to quantify the difference in welding performance between the Nd: YAG and the Yb-fibre laser. At an output power of 4kW focused in a 0.4mm diameter spot, the Yb-fibre laser was capable of a 30% higher welding speeds in 4mm (5083) aluminium alloy, or a 20% increase in depth of penetration for welding speeds between 1 and 15m/min, compared with the Nd: YAG laser. This improvement in welding performance, together with an output power of 7W, produced full penetration in 12.7mm thickness (aerospace-grade) AI-Zn-Mg-Cu aluminium alloy using the Yb-fibre laser autogenously, or in a hybrid configuration with a MIG arc. Both the autogenous laser and hybrid laser-MIG process were capable of producing welds with a weld metal porosity in line with the BS EN 13919-2 and AWS D17.1 benchmark conditions, at welding speeds of 0.55 and 0.75m/min, respectively. At these production rates, the 248 metres of stringer incorporated in a typical aluminium wing structure can be welded in 7.5 and 5.5 hours, in case of autogenous laser and hybrid laser-MIG, respectively, compared with 37.6 hours currently needed for the riveting process.