Direct numerical simulation and wind tunnel experiments have been used to study the effects of free-stream turbulence on axisymmetric wakes. In both cases the wake was introduced to various turbulent streams having various levels of turbulence intensity and length scales. It was found that the presence of the free-stream turbulence changes the wake’s decay rate and does not allow self-similarity to occur (unless maybe very far downstream and way beyond the current measurements reached). Also, the free-stream turbulence was found to be causing a significant transformation in the turbulence structure inside the wake, where the latter was found to be gradually evolving towards the former. Last, the fact that the two approaches were modelling two different problems led to some differences in their results emphasising the importance of the flow structure around the wake generating body in shaping the far wake region.

Brownout is the name given to the degraded visual environment that can develop around a helicopter as it operates in dusty conditions. The dust cloud produced reduces visibility and makes landing the helicopter extremely difficult, there is potential for damage to the aircraft or even loss of life. This thesis works towards understanding the physical processes occurring in the generation of the dust cloud and the application of this understanding in a computational model for dust entrainment. Current brownout simulations use empirical entrainment models originally developed for aeolian sand movement. These models use parameters fitted to experimental evidence, whilst they may recreate the dust conditions of certain scenarios there is need for a physical model that can produce accurate results for prospective aircraft or scenarios. The physical brownout system is a multiphase system made up of particle dynamics of the scales less than a millimetre and fluid scales as large as metres. In this thesis computational modelling of particle systems, fluid systems and multiphase flow systems are used to understand how the rotor wake entrains particles. A model scale 3D unsteady rotor simulation was performed both in and out of ground effect. The flow compares well with experimental results. The ground vortex interaction is quantified. The model scale analysis is complemented by a full scale but steady, 2D, axisymmetric rotor flow analysis. The steady flow is demonstrated to provide sufficient aerodynamic force to lift typically medium sized particles from the ground. The Discrete Element Method is a Lagrangian particle simulation method, in this thesis it is investigated numerically and then the physical behaviour is assessed in a simulation of a probe indentation experiment. The dynamic behaviour matched the experiment well. The Discrete Element Method is recommended as a particle modelling method for a brownout modelling solution. Modelling brownout is extremely difficult due to the range of scales involved. This thesis provides an in depth understanding of the helicopter flow field at small and large scales and the aerodynamic forces and entrainment mechanisms of particles on the ground in the wake of a helicopter.

Engineering design involves the production of large volumes of data. These data are a sophisticated mix of high performance computational and experimental results, and must be managed, shared and distributed across worldwide networks. Given limited storage and networking bandwidth, but rapidly growing rates of data production, effective data management is becoming increasingly critical. Within the context of Airbus, a leading aerospace engineering company, this thesis bridges the gap between academia and industry in the management of engineering data. It explores the high performance computing (HPC) environment used in aerospace engineering design, about which little was previously known, and applies the findings to the specific problem of file system cleaning. The properties of Airbus HPC file systems show many similarities with other environments, such as workstations and academic or public HPC file systems, but there are also some notably unique characteristics. In this research study it was found that Airbusfile system volumes exhibit a greater disk usage by a smaller proportion of files than any other case, and a single file type accounts for 65% of the disk space but less than 1% of the files. The characteristics and retention requirements of this file type formed the basis of a new cleaning tool we have researched and deployed within Airbus that is cognizant of these properties, and yielded disk space savings of 21.1 TB (15.2%) and 37.5 TB (28.2%) over two cleaning studies, and may be able to extend the life of existing storage systems by up to 5.5 years. It was also noted that the financial value of the savings already made exceed the cost of this entire research programme. Furthermore, log files contain information about these key files, and further analysis reveals that direct associations can be made to infer valuable additional metadata about such files. These additional metadata were shown to be available for a significant proportion of the data, and could be used to improve the effectiveness and efficiency of future data management methods even further.

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This research is concerned with the design of adaptive structures for achieving global multi-shape morphing aerodynamic configurations, by using slender structures. The proposed methodologies pursue two threads towards global optimisation of morphing structures, by providing means of aerodynamic enhancement, using efficient structural shape optimisation. A heuristic approach is proposed in this work that enables morphing through a range of stable cambered airfoils to achieve aerodynamic properties for different manoeuvres, with the benefit of low powered actuation control. This allows large changes in shape by exploiting a range of incremental non-linear structural solutions while keeping prescribed flow characteristics on an aeroelastically stable airfoil. Such an heuristic argument provides basis for global shape control of three-dimensional wings and is applied to aerodynamic design to provide enhanced roll control. A hierarchical strategy is employed, interleaving parameterisation enhancement followed by structural optimisation into the aerodynamic design process, such that the design paradigm, in conjunction with global approximation techniques, is emphasized by enhanced roll while drag is minimised. This figure of merit is complemented by structural metrics and constraints so as to maintain product integrity.

From the perspective control practitioners, control of dynamics systems subjected to varying parameters is not a new topic. However systematic methods to accommodate such problems are relatively few and recent. This thesis addresses a subset of such problems falling under the nomenclature of Reconfigurable Control Systems in relation to flight control applications. A survey in the initial phase of research indicated a wide range of ad-hoc solutions with relatively brittle or non-existent theoretical guarantees towards to the stability of the entire system. Often the reconfigurable architecture consists of multiple conceptual components performing task of identifying system parameter changes, monitoring degradation in system performance and eventually finding some corrective action to regain lost performance. The change in system parameters if attributed to faults and damages to system, then the task of the control system is to achieve fault tolerance. Such fault tolerance is of high interest for flight control community since such a control system adaptation may lead to accommodation of real life faults during aircraft operation such as control surface damages, hydraulic actuation failures etc. The thesis work aims towards developing online control redesign methods capable of taking into account realistic requirements. The goals are 1) To find control input values in presence of faults. 2) Accommodate changes in performance criterion in presence of faults and, 3) Incorporate actuator limitations such as rate and position bounds. The research work is divided in three subparts. The initial phase consists of a study of existing solutions and methods capable of providing reconfigurable flight control architectures. This phase also covers some flight control literature relevant in the context of faults. Though the conclusions of this initial phase seem theoretically simple and straight forward, it is interesting to understand the amount of time and efforts invested by real world flight control practitioners to deduce these results. Essentially the work flow of this research work stems from practical requirement eventually leading to theoretical developments that can approximate the requirements often demanded by the people in field. The second phase consists of study and application of existing Model Predictive Control methods to the field of reconfigurable flight control. MPC has been successful in major complex control problems due to its online constrained optimisation methodology. Along-with certain theoretical extensions it is well capable of providing a successful means to redesign control action online in presence of failures. Simulation studies of sufficient fidelity and complexity on a full envelop fighter aircraft nonlinear model prove such control reconfiguration capabilities of MPC. Some new extensions of MPC have been developed to show it performing in a superior manner to conventional nominal formulations. The third phase of the research work focuses on further theoretical developments in the field robust adaptive control in MPC frame of operation. A new MPC formulation is derived which can accommodate constraints, uncertainty and constant disturbances (due to failed inputs). The novelty lies in the theoretical properties of this MPC as under certain conditions it is guaranteed to be asymptotically stable. This setup implements an optimization problem more complex than that of the nominal case. Typically, when disturbances and uncertainties are incorporated into the performance measure within MPC formulations, mini-max (worst-case) NP-hard problems can arise. The thesis contributes to the theory of robust synthesis by proposing a convex relaxation of a mini-max based MPC controller by adopting a Linear Matrix Inequality (LMI) optimisation formulation.

High-order accurate numerical simulations are performed to investigate the effects of wavy leading edges on aerofoil gust interaction (AGI) noise. The present study is based on periodic velocity dis-turbances predominantly in streamwise (x-) and vertical (y-) directions that are mainly responsible for the surface pressure fluctuation of an aerofoil. The perturbed velocity components of the present gust model do not vary in the spanwise (z-) direction. In general, the present results show that wavy leading edges lead to reduced AGI noise. Under the current incident gusts, it is found that the ratio of the wavy leading-edge peak-to-peak amplitude (LEA) to the longitudinal wavelength of the incident gust (λg) is the most important factor for the reduction of AGI noise. It is observed that AGI noise reduces with increasing LEA/λg, and significant noise reduction can be achieved for LEA/λg≥0.3. The present results also suggest that any two different cases with the same LEA/λg lead to a strong similarity in their profiles of noise reduction relative to the straight leading-edge case. The wavelength of wavy leading edges (LEW), however, shows minor influence on the reduction of AGI noise under the present gust profiles used. Nevertheless, the present results show that a meaningful improvement in noise reduction may be achieved when 1.06LEW/λg 61.5. In addition, it is found that the beneficial effects of wavy leading edges are maintained for various angles of attack and aerofoil thicknesses. Also, wavy leading edges remain effective in reducing AGI noise for gust profiles containing multiple frequency components. It is discovered in the current research that wavy leading edges result in in-coherent response time to the incident gust across the span, which causes a decreased level of surface pressure fluctuations, hence a reduced level of AGI noise.

A study was performed to investigate and optimize the application of perforated fairings for landing gear noise control. The sparse knowledge about this new subject has necessitated a more fundamental study involving a basic fairing-strut configuration, followed by wind tunnel tests on a simplified landing gear configuration incorporating perforated fairings. For the basic configuration, various exchangeable perforated half-cylindrical shells shrouding a circular cylinder were the subject of aerodynamic and acoustic tests. A qualitative and quantitative description has been given of the influence of perforated fairings on time averaged and unsteady flow and the related acoustics. The bled air through the shell prevents the formation of large scale vortices associated with the shell and thereby reduces low frequency noise. However, a test with a noisy H-beam replacing the circular cylinder has indicated that increasing porosity can result in adverse noise effects due to the bled mass flow washing the strut. Shearing flow past the perforate has been shown to create adverse self-noise of which both intensity and spectral content are dictated by the local velocity past the perforate. The application of perforated fairings to the simplified landing gear model reduces the low frequency noise introduced by the solid fairings to values below the baseline landing gear configuration in both side and ground view directions. Exposing the perforate outside the stagnation area does not yield extra noise reduction but introduces perforate self-noise. The synthesis of the conducted studies has shed new light on the application of perforated fairings for landing gear noise control. In particular the effects of porosity and perforation location have been clarified. However more research is needed for further optimization of these parameters.

With the rebirth of special warfare in the last few years, the role of the individual soldier and of squad-sized units has been re-emphasized. Most guerilla-type fighting has been, is presently, and will most likely continue occurring in remote areas of the world. The terrain encountered may be tropical grasslands and canopy areas, or rugged mountains, inland waterways, swamps, mud flats and rice paddies. Other adverse terrain conditions are frequently encountered and must be crossed to accomplish the mission of the unit.

A secondary task measure was used to evaluate the effects of various automobile handling characteristics on driver workload. The study was performed using the VPI & SU driving simulator, a variable speed random number generator and display, plus other control and recording equipment. Workload scores for 82 subjects were determined under various combinations of wind and curvature disturbances, vehicle steering gain, and vehicle response time. Driving performance was analyzed to measure intrusiveness of the secondary task and to confirm workload differences. The results showed definite differences across the levels of combined wind and curvature. These supported the assumption that the secondary task measure would be capable of measuring differences in driver workload. No significant differences in workload scores were obtained for changes in steering gain or vehicle response time. The secondary task did intrude on the primary task, indicating that its use may cause experimental complications. The method and equipment appear to be useable in either simulator or on-the-road vehicles. / Master of Science