Excess noise from gas turbine exhausts

There is evidence to show that the exhaust noise from gas turbines contains components which exceed the jet mixing noise at low jet velocities. This paper describes a theory developed to calculate the acoustic power produced by temperature fluctuations from the combustor entering the turbine. Using the turbine Mach numbers and flow directions at blade mid-height, and taking a typical value for the fluctuation in temperature, it has been possible to predict the acoustic power due to this mechanism for three different engines. In all three cases the agreement with measurements of acoustic power at low jet velocities is very good. Using a measured spectrum of the temperature fluctuation the prediction of the acoustic power spectrum agrees quite well with that measured

The generation of noise by the fluctuations in gas temperature into a turbine

An actuator disc analysis is used to calculate the pressure fluctuations produced by the convection of temperature fluctuations (entropy waves) into one or more rows of blades. The perturbations in pressure and temperature must be small, but the mean flow deflection and acceleration are generally large. The calculations indicate that the small temperature fluctuations produced by combustion chambers are sufficient to produce large amounts of acoustic power. Although designed primarily to calculate the effect of entropy waves, the method is more general and is able to predict the pressure and vorticity waves generated by upstream or downstream going pressure waves or by vorticity waves impinging on blade rows

Emerging HIV communities and self : the representation of self and community in South African HIV/AIDS literature

Includes bibliographical references (leaves 73-75).HIV/AIDS is a prominent part of contemporary South African experience that has found expression in many forms, one of which is literature. This thesis analyses the relation between self and community as it is represented in South African HIV/AIDS literature. The argument of the thesis is underpinned by a dual theoretical strand

Writing Johannesburg into Being: Rituals of Mobility and the Uneven City in Mark Gevisser, Ivan Vladislavić and Lindsay Bremner’s Writing

This article explores the role of Johannesburg in the literary imagination of three contemporary South African writers, counterposing Mark Gevisser’s memoir Dispatcher: Lost and Found in Johannesburg (2014) and Ivan Vladislavić’s semi-autobiographical work of creative non-fiction Portrait with Keys (2006) with Lindsay Bremner’s collection of personal and architectural essays Writing the City into Being (2010). These white South African authors are keenly aware of their privileged position: they use the space offered by writing to make sense of their relation to Johannesburg and the access granted to them because they have the choice either to walk or to drive. I argue that this seemingly mundane choice is indicative of the continuing inequality of post-apartheid South African society, and that this is foregrounded in Bremner, Gevisser and Vladislavić’s literary writing as they use personal rituals of urban mobility to index and expose the boundaries and continuing unevenness of the city.&nbsp

Aerodynamics of aircraft engines : stride and stumbles

September 1992Includes bibliographical references (leaves 21-22)Summary: Attempts to understand and predict the aerodynamic behaviour of compressors and turbines in aircraft gas turbines have been encouraged by the intense competitive pressure which exists. Many of the apparently most difficult problems have been overcome using suitable numerical analysis, for example the calculation of three-dimensional transonic flows has been particularly successful. It is seemingly paradoxical that the numerical methods are relatively very good for flows which are traditionally regarded as difficult, but do less well at predicting efficiency when the flow is well behaved in the conventional aerodynamical sense, such as fully attached flows. The numerical methods do not necessarily give insight into the flow that is seen as most helpful to the designer and it can be useful to complement them with simpler approaches to the problem which seek to capture the essential features of the flow. The aerodynamics of aircraft engine fans are used to illustrate these points. Although numerical methods have been very successful with aeroengine fan blading they have been less successful with the multistage compressor. The reasons for this, primarily the difficulty of prescribing the boundary conditions, are discussed in this paper. The analysis of flow in multistage compressors still stumbles along with empirical methods, much of it based on data published over twenty years ago. A second area where stumbling has occurred is the prediction of flutter of blading, particularly fan blading; as recently as 1990 there were major in-flight failures due to flutter of a fan in civil airline service. To this day there is no reliable method of predicting the operating boundaries of flutter, and testing the engine over the entire operating range of altitude and speed is the only reliable method of ensuring safe operation.Supported by the Dept. of Aeronautics and Astronautics at MI

“Lean[ing] into transcendence”: Transformations of the Sacred in South African, Zimbabwean and Nigerian Literatures

Enchantment is a defining feature our postcolonial, globalised world and the literary is where much of this wonder is registered and celebrated. Thus this thesis attends to the postcolonial dynamic of sacred and secular experience as it is represented in contemporary African literatures. Debates around the secular and postsecular are long standing in the fields of religious studies, anthropology and philosophy, but as yet underappreciated in literary studies. I develop a hermeneutic of the imminent sacred as a way to read the constitutive and recuperative gestures subjects make as they assert a sense of belonging in spaces of globalised modernity. The texts are grouped thematically. In response to Chris Abani and Yvonne Vera’s work I articulate how the ritual dimensions of lyrical prose and ritual attention to the corporeal form sacralises the body. Phaswane Mpe and Teju Cole incorporate African epistemologies into the resignification of their cities and with Ivan Vladislavić, the streets are sacralised. Marlene van Niekerk and J. M. Coetzee convey the anxieties of settler colonialism and a love of land reinscribed as sublime. Collectively, the novels I discuss reflect patterns of existential anxiety that emerge from difficulties of belonging, and I trace the ritualised and sacralising strategies of incorporation that seek to locate the subject. These novels radically disrupt the epistemological and ontological modalities of globalised ‘secular’ literary production and intervene in the recuperation of the sacred as a mode of incorporation and resistance. Recent scholarship in African literatures has overlooked these distinctly postsecular negotiations and the ways in which the sacred is reinvested in contemporary African fiction in order to instantiate intimate, local alternatives to the teleology of secular modernity. Thus I use the imminent sacred as a reading strategy that foregrounds these postsecular negotiations and the interrelations of care and vulnerability that motivate sacralisation

Future aircraft cabins and design thinking: optimisation vs. win-win scenarios

With projections indicating an increase in mobility over the next few decades and annual flight departures expected to rise to over 16 billion by 2050 there is a demand for the aviation industry and associated stakeholders to consider new forms of aircraft and technology. Customer requirements are recognised as a key driver in business. The airline is the principal customer for the aircraft manufacture. The passenger is, in turn, the airline’s principal customer but they are just one of several stakeholders that include aviation authorities, airport operators, air-traffic control and security agencies. The passenger experience is a key differentiator used by airlines to attract and retain custom and the fuselage that defines the cabin envelope for the in-flight passenger experience and cabin design therefore receives significant attention for new aircraft, service updates and refurbishments. Decision making in design is crucial to arriving at viable and worthwhile cabin formats. Too little innovation will result in an aircraft manufacturer and airlines using its products falling behind its competitors. Too much may result in an over-extension with, for example, use of immature technologies that do not have the necessary reliability for a safety critical industry or sufficient value to justify the development effort. The multiple requirements associated with cabin design, can be viewed as an area for optimisation, accepting trade-offs between the various parameters. Good design, however, is often defined as developing a concept that resolves the contradictions and takes the solution towards a win-win scenario. Indeed our understanding and practice of design allows for behaviours that enhance design thinking through divergence and convergence, the use of abductive reasoning, experimentation and systems thinking. This paper explores the challenges of designing the aircraft cabin of the future that will deliver on the multiple requirements. In particular the paper explores the value of implementing design thinking insights in engineering practice and discusses the relative merits of decisions based on optimisation verses win-win scenarios for aircraft cabin design and wider applications in aerospace environments. The increasing densification of technological opportunities and shifting consumer demand coupled with highly complex systems may ultimately challenge our ability to make decisions based on optimisation balances. From an engineering design perspective optimisation tends to preclude certain strategies that deliver high quality results in consumer scenarios whereas win-win solutions may face challenges in complex technical environments

Using shock control bumps to improve transonic fan/compressor blade performance

Shock control bumps can help to delay and weaken shocks, reducing loss generation and shock-induced separation and delaying stall inception for transonic turbomachinery components. The use of shock control bumps on turbomachinery blades is investigated here for the first time using 3D analysis. The aerodynamic optimisation of a modern research fan blade and a highly loaded compressor blade are carried out using shock control bumps to improve their performance. Both the efficiency and stall margin of transonic fan and compressor blades may be increased through the addition of shock control bumps to the geometry. It is shown how shock induced separation can be delayed and reduced for both cases. A significant efficiency improvement is shown for the compressor blade across its characteristic, and the stall margin of the fan blade is increased by designing bumps that reduce shock-induced separation near to stall. Adjoint surface sensitivities are used to highlight the critical regions of the blade geometries, and it is shown how adding bumps in these regions improves blade performance. Finally, the performance of the optimised geometries at conditions away from where they are designed is analysed in detail

The Interaction of Entropy Fluctuations with Turbine Blade Rows; A Mechanism of Turbojet Engine Noise

The theory relating to the interaction of entropy fluctuations ('hot spots'), as well as vorticity and pressure, with blade rows is described. A basic feature of the model is that the blade rows have blades of sufficiently short chord that this is negligible in comparison with the wavelength of the disturbances. For the interaction of entropy with a blade row to be important, it is essential that the steady pressure change across the blade row should be large, although all unsteady perturbations are assumed small. A number of idealized examples have been calculated, beginning with isolated blade rows, progressing to single and then to several turbine stages. Finally, the model has been used to predict the low-frequency rearward-radiated acoustic power from a commercial turbojet engine. Following several assumptions, together with considerable empirical data, the correct trend and level are predicted, suggesting the mechanism to be important at low jet velocities