No description available.

No description available.

When partially closed, steam turbine governing valves rely on flow separation from the valve head and seat to generate loss and throttle the flow. The aim of this type of valve is to avoid separation and therefore eliminate loss when the valve is fully open, and to have stable and controllable separations at all other valve lifts. Any significant unsteadiness in the valve flow can result in unacceptable mechanical vibration of the valve, which in extreme cases can lead to failure. Results will be discussed from work that has been undertaken into valve flow instabilities at Leicester University Engineering Department in collaboration with Alstom Energy Ltd. At high lifts, the Mach number of the steam flow between the head and the seat is sufficiently low for the fluid to be considered as incompressible. Water was therefore used as the working fluid in the tests at Leicester to model accurately the flow in a fifth scale acrylic model valve under high lift conditions. Results from laser light sheet visualisation, Particle Image Velocimetry and transient pressure measurements of the valve flow are presented. Laser light sheet illumination and high-speed Cine photography have been used to visualise the highly three dimensional valve flow. A range of valve head geometries has been tested. The results of the flow visualisation show the presence of stable and unstable separation zones and their influence on the valve flow. Particle Image Velocimetry has provided quantitative information on these features. Methods for stabilising the separation zones by modifying the valve head and seat have also been investigated and the results from these tests have shown improvements in reducing valve exit pipe unsteadiness.

No description available.

A school of literature has shown that Annexin-A1 (Anx-A1) is an endogenous anti-inflammatory protein that exerts a regulatory control over the innate immune system in order to restore homeostasis after an inflammatory reaction. Surprisingly, recent published works have highlighted that Anx-A1 has an alternate role in the adaptive immune system by positively modulating the strength of TCR signalling and biasing helper-subset differentiation. Dendritic cells are a class of innate leukocytes, poised at the environmental interface, that are the essential immune cells responsible in the initiation of T-cell driven responses. These findings provided the foundation for this PhD project, the principal aim of which is to provide a link between the disparate effects of Annexin-A1 in innate and adaptive immunity by investigating the role of endogenous Annexin-A1 in dendritic cell biology and its effector function as an antigen-presenting cell towards T cell activation and differentiation. To address this hypothesis, I cultured bone marrowderived dendritic cells from AnxA1-deficient mice or control littermates and stimulated with LPS (100ng/ml) then compared phenotypic and functional characteristics. My results demonstrate that Anx-A1-/- bone marrow derived dendritic cells show an increased number of CD11c+ cells expressing high levels of some maturation markers such as CD40, CD54 and CD80 and a decreased capacity to take up antigen compared to control Anx-A1+/+ cells. However, analysis of LPS-treated dendritic cells from Anx-A1-/- mice demonstrated a diminished up-regulation of maturation markers, a decreased migratory activity in vivo and an attenuated production of the inflammatory cytokines Interleukin (IL)- 1β, Tumour Necrosis Factor (TNF)-α and IL-12. This defect was resultant of an impaired Nuclear Factor (NF)-κB/DNAbinding activity due to lack of Anx-A1 signalling as demonstrated by the reduced activation of Extracellular-signal Regulated Kinase (ERK) 1/2 and protein kinase B (PKB)/Akt compared to cells from control littermates. As a consequence of these defects, I assessed the antigenpresenting/ T-cell activating capabilities of these DC. Anx-A1-/- DC showed an impaired capacity to stimulate T cell proliferation and differentiation in allogeneic mixed leukocyte reaction. To dissect this biologically relevant phenomenon further, I employed an antigenspecific, T-cell restricted model; a co-culture system of chicken ovalbumin peptide-pulsed, LPS-matured bone marrow-derived DC incubated with transgenic TCR T cells from OT-I/RAG-1-/- (OT-I, OTI/ CD8+) or OT-II/ RAG-1-/- (OT-II, OT-II/CD4+) mice. Peptide-pulsed, LPS-matured AnxA1-/- DC failed to initiate an appropriate T cell activation in both OT-I and OT-II T cells indicated by reduced cell proliferation when compared to T cells co-cultured with peptide6 pulsed, LPS-matured AnxA1+/+ DC. Additionally, comparison of peptide-pulsed, LPS-matured AnxA1-/- DC with AnxA1+/+ DC counterparts detected severely diminished levels of IL-2 from cocultures with OT-I T cells and ablated IFN-γ production from cocultures with both OT-I and OT-II T cells. In conclusion, AnxA1 seems to act as a positive modulator of immunogenic activation of DC, whereby the AnxA1 signal pathway has a probable synergism with the TLR4 signalling cascade. DCderived AxnA1 appears to contribute in promoting T cell activation with a larger influence on OT-I/CD8+ T cells than OT-II/CD4+ T cells. Altogether these findings suggest that inhibition of Anx-A1 expression or function in dendritic cells might represent a useful way to modulate the adaptive immune response and pathogen-induced T cell-driven immune diseases.

The work carried out during this engineering doctorate degree has led to significant advances in the application of photographic measurement techniques to the characterisation of coarse water in wet steam flow, with particular emphasis on the development of a compact measurement probe suitable for application in a low-pressure steam turbine. Through the application of pulsed LED illumination for the first time in a compact probe, photographs at high magnification with excellent resolution are obtainable at significantly shorter exposure times than others reported in the literature. This has the advantage of reducing motion blur enabling reliable quantitative analysis to take place. Secondary to this, the coupling of high magnification, high resolution photography with pulsed LED illumination has been shown to provide a powerful research tool for flow visualisation across a range of applications, at an order of magnitude lower cost than commercial solutions employing pulsed laser illumination for the same purpose. This builds on the work of others elsewhere in the literature, but again has been proven at shorter exposure times enabling higher magnification with reduced motion blur. Finally a flexible optical test rig has been designed and manufactured, to act as an experimental test-bed for both photographic and phase-Doppler measurements on two-phase steam and air-water sprays. Phase-Doppler anemometry measurements have been performed on an accelerated jet of two-phase steam in order to perform size and velocity measurement of liquid droplets. This acts as a proof-of-concept for the technique in wet steam given the appropriate optical access. In addition phase-Doppler measurements of an air-atomising water nozzle were used as a validation data set to assess the accuracy and reliability of quantitative data from the photographic probe. In this case quantitative data was extracted from the images through application of a custom-designed image processing algorithm, designed to extract droplet size and velocity information from double-exposure droplet images. In general agreement is good within 10-15% of the PDA measurements. Photographic and PDA measurements have also been taken of an LP spray nozzle, as used in the Alstom model steam turbine test facility. These tests have demonstrated significant differences in the spray characteristics when spraying into air and into vacuum conditions. This provides useful insight for the positioning and application of these spray nozzles in a steamturbine environment.

A computational study aimed at improving the understanding of rotating instability in the LP steam turbine last stage working under low flow rate conditions is described in this thesis. A numerical simulation framework has been developed to investigate into the instability flow field. Two LP model turbine stages are studied under various flow rate conditions. By using the 2D simulations as reference and comparing the results to those of the 3D simulations, the basic physical mechanism of rotating instability is analysed. The pressure ratio characteristics across the rotor row tip are found to be crucial to the inception of rotating instability. The captured instability demonstrates a 2D mechanism based on the circumferential variation of unsteady separation flow in the rotor row. The 3D tip clearance flow is found not a necessary cause of the instability onset. Several influential parameters on the instability flow are also investigated by a set of detailed studies on different turbine configurations. The results show that the instability flow pattern and characteristics can be altered by the gap distance between the stator and rotor row, the rotor blading and the stator row stagger angle. Some flow control approaches are proposed based on the observations, which may also serve as design reference. The tip region 3D vortex flow upstream to the rotor row is also captured by the simulations under low flow rate conditions. Its appearance is found to be able to suppress the inception of rotating instability by disrupting the interaction between the rotor separation flow and the incoming flow. Finally, some recommendations for further work are proposed.

Specific power output from a Low Pressure (LP) steam turbine can be enhanced by increasing the stage efficiency or raising its pressure ratio; both methods are interlinked and must be dealt with together. The latter is achieved by connecting to the exhaust diffuser; space and cost constraints often insist the use of an axial-radial diffuser with high levels of diffusion. The present study aims to investigate the interaction between the last-stage blade and the axial-radial diffuser, which can influence the diffuser performance and thus the total work output from the stage. This work is carried out using CFD simulations of a generic last stage low pressure (LP) turbine and axial-radial exhaust diffuser attached to it. In order to determine the validity of the computational method, the CFD predictions are first compared with data obtained from an experimental test facility. A computational study is then performed for different design configurations of the diffuser and rotor casing shapes. The study focuses on typical flow features such as effects of rotor tip leakage flows and subsequent changes in the rotor-diffuser interactions. The results suggest that the rotor casing shape and diffuser configurations influences the rotor work extraction capability and yields significant improvements in the static pressure recovery.

A combination of climate change, due to anthropogenic CO2 emissions and concerns over energy security, due to fluctuating fuel prices, has led to the UK pushing to increase its renewable energy production. Harnessing tidal stream energy is an infant sector in the UK’s renewable energy portfolio, despite the UK’s large tidal stream resource, and is harnessed through deploying tidal stream energy converters. This thesis focuses on the design of a novel vertical axis tidal turbine (VATT) called CarBine which is driven by drag force and therefore has several unique advantages, including slow rotational speed, omni-directionality and a simple design. This research focused on the optimisation of the CarBine design and was split into two areas: physical testing and numerical modelling. A conventional Savonius was also analysed in both of these respects and this enabled a direct comparison of CarBine to a competing drag force driven VATT. Physical testing measured the power of the turbines and was conducted in hydraulic flumes at both Cardiff University (CU) and IFREMER in Northern France for a range of flow conditions. Testing at IFREMER enabled the quantification of the blockage effect in the CU experiments. Physical testing resulted in the optimised design of CarBine being one with a four arm configuration. From physical testing at CU, CarBine showed inferior efficiency performance to that of the conventional Savonius, a Cp of 0.117 compared to 0.225 at U∞=0.72 m/s. As a result a hybrid of both the Savonius and CarBine was tested, namely a Savonius with flaps. However, results from physical testing showed the Savonius with flaps to have inferior performance to both CarBine and the conventional Savonius, with a Cp of 0.103 at U∞=0.72 m/s at CU. Numerical modelling was conducted using the commercial CFD software package, Ansys CFX. Both transient and steady state simulations along with 2D and 3D models were used to model both CarBine and the Savonius. Both the k-ε and SST turbulence models were used for comparison. The two degrees of rotational freedom present in the CarBine design resulted in CarBine being difficult to model precisely. The numerical modelling results were validated against the physical testing results and where available, 3D results showed closer validation than the 2D results.