No description available.

Investigations were completed in two areas of research. Firstly mechanical compression test coupons of unidirectional carbon fibre composite were optimised to produce repeatable and reproducible data to support automotive structural applications. The compressive strength was determined through ASTM D 695 M testing, and the results were correlated with test variations implemented. Various preparation methods were evaluated in the determination of the cause of variation found in unidirectional carbon fibre test specimens. Analytical tools were implemented, including microscopical techniques, Scanning Electron Microscope, Talyscan and X-Ray Tomography to determine initiation of failure and to quantify the damage encountered by the compressive test specimen. The findings correlated well with the mechanical test results, which indicate that the higher quality laminates in terms of surface and edge finishes will have better mechanical properties compared to lower quality composites. Secondly, the characterisation of the surface of a material designed for automotive body applications. The CBS 95 is manufactured by Gurit UK and has been designed to be the first carbon fibre material to be cured using vacuum bagging and have no evidence of print through at the surface. Various characterisation tools, including Proscan 2000, microscopical techniques, and Dynamic Mechanical Analysis, were used to evaluate anomalies found at the surface of the components manufactured from CBS 95. The origin and formation mechanisms of the anomalies was sought and explained with use of models and the analytical equipment, two main origins were found: porosity and kitting defects. Additionally, the sustainability of CBS 95 exposed to harsh environments was investigated. The CBS 95 was exposed for 20 weeks in three different environments (hot/dry, hot/wet and chemical). Analytical techniques such as MINOLTA Spectrophotometer CM-500 Series, Gloss analyser and microscopical techniques were used to quantify the environmental degradation of the CBS 95. The CBS 95 performed consistently in each of the three environments. The work has also made many recommendations for improved manufacturing routes for both the compressive test specimen and the CBS 95, reducing processing time and improving quality. These suggestions, when considered together, contribute significantly to carbon fibre manufacturing.

Complex space missions involving formation flying or drag compensation are driving the need for spacecraft propulsion systems capable of providing low but also highly accurate thrust levels. Currently, no single propulsion device exists that is able to provide both precision and coarse thrust capability over the micro-Newton to milli-Newton thrust range required by these missions. A need for a precision, low thrust, miniature electric propulsion device with a wide throttling range therefore exists. The concept of a differential ion thruster was initially proposed by the Ion Propulsion Group of QinetiQ to address this requirement. It was proposed that an unprecedented throttling range and thrust resolution could be achieved through differential control of opposing ion beams, by which very small net offsets in thrust could be achieved. Single ion beam operation, as for conventional gridded ion thrusters, would permit higher thrust levels to be achieved with high specific impulse. The extraction and independent control of two ion beams from a single gridded ion thruster has never previously been reported. Prototype and breadboard models of the proposed Miniaturised Differential Gridded Ion Thruster (MiDGIT) were designed and manufactured in collaboration with QinetiQ to provide a proof-of-concept and to demonstrate preliminary performance. Test campaigns were conducted at the QinetiQ Large European Electric Propulsion Facilities and within the EP1 vacuum chamber at the University of Southampton. The work reported in this thesis contributes to the first detailed characterisation of a twin-ended radio frequency gridded ion thruster utilising a common plasma discharge. Two control methods were identified which permitted independent control of the ion beams extracted from either end of the thruster. These were: variation of the accelerator grid potential in order to induce changes in the plasma sheath geometry upstream of each screen grid leading to variations in the extracted ion currents, and variation of the RF power delivered to each end of the thruster to generate a higher plasma density on one end of the discharge and ultimately a net thrust out of that end of the thruster. The performance of the MiDGIT thruster has been evaluated with regards to both coarse thrust and fine thrust control requirements. Though the MiDGIT thruster has demonstrated a wide thrust range surpassing competing single-ended miniature ion thrusters, the extraction of two ion beams to achieve very low thrust levels leads to low specific impulse and high specific power for the MiDGIT thruster compared to any other single-ended ion thruster that can achieve the same thrust levels. Recommendations to improve efficiency are made and suggestions for future work and further development of the MiDGIT thruster are given.

An experimental investigation examined the capability of dielectric barrier discharge (DBD) actuators to control a high-lift device system. Aerodynamic tests investigated the potential of utilising the actuator to control the flap side-edge vortex flow field. Acoustic tests examined the attenuation of slat noise with a DBD actuator. The sparse knowledge related to the control of a vortex flow field with a DBD actuator necessitated a more fundamental study that used a NACA 0015 wing. From this study, it was shown that the application of control resulted in a more diffused tip vortex. The actuator's ability to control the evolving vortex flow field was weakly dependent on the Reynolds number but strongly dependent on the angle of attack. Consequently, a DBD actuator was applied to a flap side edge. However, it was concluded that the actuator had no discernible effect on the flow field due to its addition of momentum being too low to destabilise the formation of the flap side-edge vortex. The slat research concerned the attenuation of the leading-edge component of high-lift device noise. At an angle of attack of two degrees, several tonal noise components with broadband content appeared in the slat noise spectrum. These noise features were successfully suppressed with a DBD actuator operating in open-loop control. For closedloop control, a quasi-static feedback controller was implemented. Comparable levels of performance were obtained for both control methods with more than a 20 dB reduction achieved in the dominant tonal noise feature. The research conducted shed new light on the application of DBD actuators to control the high-lift device system. However, further research is needed if the device is to be utilised to control flap side-edge flow field. The attenuation of slat tonal noise with broadband content was achieved with the actuator.

No description available.

A tunable arc transient technique was developed to measure the duct exit response to sound in subsonic flow. An assymptotic formulation based upon the theory of sound radiation from a duct exit in flow by Munt, was developed. Experimental and theoretical results were compared to enhance the current understanding of core radiation from a turbofan aeroengine. An intense, arc discharge acoustic source tunable in both level (145-170dB induct) and frequency bandwidth, was developed. The radiated sound was predictable from arc current alone and was the basis of a transient method. The transient method developed in flow was shown to be useful in measuring duct propagation attenuation, sound pressure reflection coefficients, transmission coefficients and radiation directivities of the duct exit. These results compared well to other experimental methods. The assymptotic theory developed, used large argument expansions for the decomposition of the Wiener-Hopf kernel in the approximations by Cargill to the Fourier integral formulation by Munt. The theory, valid for plane wave sound radiation in the flight and static cases for Ka> 05, shows excellent agreement to Levine and Schwinger's results. The theory and transient test, identified nine flow effects to the radiation of sound from a duct exit. Flow convection scales as four powers of doppler factor. Enhancement of diffraction of sound into forward arc. Radiation interference pattern familiar to classic piston directivity. Radiation interference pattern shifts with cone of silence. Exponential mean flow refraction valley about the jet axis. Transmission coefficient across the jet/external interface. In the flight case, additional effects relative to the static case are: For equal external and jet mean flow velocities, flow convection scales as two powers of doppler factor. The cone of silence angle decreases. Radiation interference pattern becomes more constructuve in forward arc.

No description available.

The aircraft industry has been at the forefront in developing design optimization strategies ever since the advent of high performance computing. Thanks to the large computational resources now available, many new as well as more mature optimization methods have become well established. However, the same cannot be said for other stages along the optimization process - chiefly, and this is where the present thesis seeks to make its first main contribution, at the geometry parameterization stage. The first major part of the thesis is dedicated to the goal of reducing the size of the search space by reducing the dimensionality of existing parameterization schemes, thus improving the effectiveness of search strategies based upon them. Specifically, a refinement to the Kulfan parameterization method is presented, based on using Genetic Programming and a local search within a Baldwinian learning strategy to evolve a set of analytical expressions to replace the standard 'class function' at the basis of the Kulfan method. The method is shown to significantly reduce the number of parameters and improves optimization performance - this is demonstrated using a simple aerodynamic design case study. The second part describes an industrial level case study, combining sophisticated, high fidelity, as well as fast, low fidelity numerical analysis with a complex physical experiment. The objective is the analysis of a topical design question relating to reducing the environmental impact of aviation: what is the optimum layout of an over-the-wing turbofan engine installation designed to enable the airframe to shield near-airport communities on the ground from fan noise. An experiment in an anechoic chamber reveals that a simple half-barrier noise model can be used as a first order approximation to the change of inlet broadband noise shielding by the airframe with engine position, which can be used within design activities. Moreover, the experimental results are condensed into an acoustic shielding performance metric to be used in a Multidisciplinary Design Optimization study, together with drag and engine performance values acquired through CFD. By using surrogate models of these three performance metrics we are able to find a set of non-dominated engine positions comprising a Pareto Front of these objectives. This may give designers of future aircraft an insight into an appropriate engine position above a wing, as well as a template for blending multiple levels of computational analysis with physical experiments into a multidisciplinary design optimization framework.

Due to increasingly stringent environmental legislation, there is a requirement for lower emissions and greater overall efficiency of light vehicle diesel (LVD) engines. This continues to be achieved through the optimisation of design and careful selection of the materials used in key LVD engine components, for example pistons, so that they are lighter and can operate at higher temperatures. Pistons are non-serviceable parts and so must be able to withstand the fatigue and high temperature environment of the car engine. It is therefore important to understand the mechanisms of fatigue in these alloys to help inform alloy development for the next generation of pistons. Pistons are typically produced from multi-component Al-Si casting alloys. These alloys exhibit a complex, multiphase microstructure comprising α-aluminium as the matrix with silicon particles and several intermetallic phases. Previous research on Al-Si casting alloys has demonstrated that porosity is detrimental to fatigue life as cracks initiate freely at pores. However, with improved casting techniques porosity can be greatly reduced and other microstructural features influence fatigue life. In particular, Si particles have been shown to play an important role in the initiation and subsequent propagation of fatigue cracks. This study assesses the role of Si content and other microstructural features on fatigue behaviour by testing a set of well-characterised multi-component, Al-Si casting alloys with varying Si content. Fatigue initiation behaviour was investigated at room temperature using S-N and short fatigue crack growth experiments. Pores, Si particles and intermetallic phases were shown to cause fatigue crack initiation. In a 0.67wt% Si containing alloy, large-scale porosity was observed and was the foremost reason for fatigue initiation. In two alloys the Al9FeNi phase was observed to be the most detrimental hard particle causing fatigue crack initiation. Nanoindentation results showed that Al9FeNi had a lower hardness and higher modulus than Si and so Al9FeNi may be expected to fracture preferentially, consistent with the fatigue results. X-ray computed tomography demonstrated that all the alloys investigated contained a complex, interconnected, intermetallic sub-structure. As a result, the micromechanisms of fatigue are different to those in conventional particulate Al-Si alloys because particle fracture is required to ensure a level of crack continuity. At room temperature and 350˚C, and at low and high crack growth rates, the crack tip may be described as a diffuse region of micro-damage and intact ligaments. It is the extent of this damage in the alloys that controls the crack growth rates exhibited and simple trends between the Si content and roughness, reported for particulate systems, do not hold true in the alloys investigated in this study. The balance of the micromechanisms of fatigue was shown to be dependent on temperature. This highlights the importance of fatigue studies at temperatures that are characteristic of those experienced in service.

This study primarily investigated the flow and aeroacoustics associated with the slat of a three-element aerofoil in approach conditions. The study assessed importance of several factors and examined their aerodynamic impacts. The factors investigated were aerofoil incidence, slat angle, slat cusp geometry, fixing transition and blowing in the slat cove. A combination of experimental and computational techniques investigated the factors selected. The experimental work employed PIV, pressure tap, a force balance, flush mounted microphones and an acoustic array. The computational work used DES along with the FW-H acoustic analogy to obtain the far-field directivity. Tonal features occurred at high incidence and originated at the slat trailing edge, due to the blunt trailing edge and gap, and at the reattachment point. Fixing transition removes the tone at the reattachment point and reduces the slat gap tone at the trailing edge but does not remove the tone generated by the blunt trailing edge. All of the tones found, only occurred at certain slat and wing settings. Broadband sound was present in all conditions but had a strong dependence on the incidence of the wing. The sound was loudest with the wing at  = 5o with a reduction as the wing incidence was increased. The broadband sound also reduced as the slat angel decreased from S = 23o. The shear incidence angle was a good indicator of the impact of these two factors on the sound generated. Extending the slat cusp reduced the broadband sound at low aerofoil incidence. However, for   10o the extension led to increased broadband sound. Neither blowing nor fixing transition had a significant impact on the broadband sound generated by the slat system. The aerodynamic loads generated by the wing were mainly dependent on the aerofoil incidence. However, other factors did influence the forces generated. Reducing the slat angle increased the lift generated by the wing especially at low aerofoil incidence but the lift to drag ratio was unaltered. At high aerofoil incidence, extending the slat cusp reduced the lift generated. Blowing and fixing transition did not significantly alter the forces generated by the wing.