This thesis describes an investigation into the use of the Time Marching method for the solution of two-dimensional nucleating flows of steam. The treatment has been applied to experimental measurements on two cascades of blade profiles a nozzle and a rotor tip section. The literature survey covers the early investigations of condensations in flowing steam, the development of nucleation theory, droplet growth laws and their applications to one dimensional steam flows. The general development of the Time Marching technique is considered next. The conservation equations governing the non-steady, two-dimensional and inviscid flows including the additional terms to allow for the two phase effects in relation to a standard H-grid are described next. This is then followed by the description of the refinements introduced to increase the accuracy of the solutions. The treatment of viscous effects is by viscous-inviscid interaction. The boundary layer equations using the integral method are described next and this is followed by the description of a base pressure model used in the calculations. A description of the experimental facility is presented next. The facility is a blow down tunnel for the study of two-dimensional two-phase flows. Blade surface pressures, density distribution, droplet size, wetness fraction and mass flow rates can be determined using the instrumentation. The results of theoretical solutions and experimental measurements are presented next. The conditions consist of superheated and nucleating flows in a nozzle and a rotor cascade. The agreement obtained between the theoretical and experimental results is satisfactory.

The thesis describes an experimental investigation of nucleating flows of steam in a cascade of nozzle turbine blading. To obtain nucleation in subsonic flows of steam, a supercooled supply is necessary which has been achieved under blow-down conditions. The literature survey covers the early investigations of condensation in flowing steam, the development of nucleation theory, droplets growth laws and their simple applications in the study of phenomena associated with condensation in nozzles. Finally some of the problems associated with wetness in turbines are considered. Next the experimental facility is described. The facility is a blow-down steam tunnel constructed for the study of two-dimensional two-phase flows. The instrumentation caters for the measurements of surface pressure distributions, wake traverses downstream of the cascade as well as for the optical observations and droplet size measurements. The main experimental chapter includes the results of the surface pressure measurements, wake traverses downstream of the cascade, flow observations and droplet size measurements. Some measurements of the thermodynamic nucleation losses are also presented together with the calibration of the probe used for the wake traverses. Comparisons of results under steam superheated and nucleating flows reveal the blades to have different characteristics when the outlets have been supersonic or sonic. The most notable difference has been the pressure rise associated with the zone of rapid condensation, its location and its insensitivity to changes in inlet temperatures and overall pressure ratios. In contrast, when the outlet has been subsonic, the blades exhibit similar characteristics under steam superheated and nucleating conditions. In addition, comparisons made with the results obtained previously by other investigators using different blades suggest that the interaction between the zone of rapid condensation and the aerodynamic performance of the blades can vary depending on the blade shape.

The thesis describes an experimental investigation of nucleating steam flows over cascades of steam turbine blading in which the characteristics of two different profiles one a nozzle and the other a rotor blade have been studied. The literature survey covers the development of nucleation theory and its application to steam flows. This is followed by the development of equations describing two-dimensional flows of nucleating steam and the description of a numerical method for their treatment using the time marching technique. The description of a short duration steam tunnel and data acquisition system suitable for the study of nucleating flows is given next. The instrumentation caters for surface pressure measurements and wake traversing downstream of the cascade. Optical arrangements for Mach Zehnder and shadowgraphy and droplet measurements by light extinction method are also included. The experimental observations have been carried out for superheated and supercooled steam flows. The measurements have been repeated for a series of overall pressure ratios covering subsonic to supersonic outlet conditions. The comparisons show features exhibited by nucleating tests which are absent from the tests in which the steam is dry.

This thesis is concerned with experimental studies of nucleating and wet steam flows over cascades of turbine blading. To simulate conditions in actual turbine flows it is necessary to produce nucleation in sub-sonic flows. has been achieved by the blow-down technique. The classical nucleation theory and the equations describing the growth of droplets are outlined in the literature survey. Application to one- and two-dimensional flows of condensing steam are also given. This is followed by a brief account of the effects of wetness on the flow through turbines.

The thesis is concerned with an experimental investigation of wet steam flows in a cascade of turbine blading. To obtain nucleation in sub-sonic flows of steam, a supercooled supply is necessary which has been achieved under blow-down conditions. To obtain wet steam, the supercooled steam generated is passed through a venturi before admission to the cascade. To evaluate the influence of droplet size two separate venturis have been used in the investigation. The literature survey covers the early investigations of condensation in flowing steam, the development of nucleation theory and droplet growth laws. A description of the experimental facility and the improvements introduced to it is given next. The facility is a blow-down steam tunnel constructed for the study of two-dimensional two-phase flows. The instrumentation caters for the measurement of pressure distributions in the venturis, blade surfaces, blade mid-passage, upstream and downstream of the cascade as well as wake traverse downstream of the cascade.

This thesis investigates the power generation potential of diffuser augmented horizontal axis tidal stream turbines. The use of diffuser augmentation for such devices is not a new concept, though many questions remained unanswered regarding the device performance and economics. This work highlighted a number of limitations within the literature on such devices and aimed to clarify the main factors which affect their performance and economics in tidal stream flows. Extant numerical modelling methods for diffuser augmented turbines were shown to produce inaccurate power prediction results due to modelling simplifications. The accurate numerical modelling of diffuser augmented turbines was made possible by the derivation of an extended blade element momentum turbine model within computational fluid dynamics. This model was verified experimentally and found to reproduce the experimental data accurately, matching both power outputs and diffuser surface pressures. The investigation was undertaken using a combination of numerical modelling and wind tunnel experimentation. It was found that effective diffuser augmentation requires a rotor with a thrust of approximately 1/2 that of a bare rotor. The rotor geometry was found to have a significant impact upon the boundary layer flows and therefore the diffusion and power output. The impact of the hub and the component geometry interactions were also highlighted. It was also found that diffuser augmentation allows sustained performance under yawed flows and potential for improvement in highly turbulent flow. It was shown that diffuser augmented devices with lower area ratios are more efficient at power capture. An economic analysis was performed, combining a derived cost model and an annual energy production analysis using real tidal stream data, incorporating flow yaw and turbulence effects. It was shown that using current technology, bare rotor type devices are the more economically viable means of power generation.

This thesis concerns the computational modelling of low pressure (LP) steam turbine exhaust hood flows. A test case for LP last stage blades (LSBs) with a full aerodynamic definition and an accompanying exhaust hood was developed which is representative of current industrial practice. The test case geometry is freely available allowing other researchers to build on this work and is the first of its kind. Studies on this Durham Stage and Exhaust Hood Test Case showed the geometry produces a representative flow pattern and performance metrics comparable to other published research. Using the test case, the effect of condenser cooling water pressure gradient on the hood flow was computed for the first time. A generic boundary condition was developed to represent the transverse condenser cooling water flow and, when applied to the test case, was shown to have a larger influence on the flow asymmetry within the hood than the tip leakage jet. This thesis describes the first application of the non-linear harmonic (NLH) method to couple the LSBs to the exhaust hood. This method enabled the circumferential non-uniformity which develops in the exhaust hood to be transferred across the interface to the stage, in half the computational demand of the full annulus frozen rotor approach. The first review of the influence of inlet circumferential asymmetry on the hood flow field highlighted that modelling its effect is not as crucial as indicated in the literature, unless the diffuser axial length is very compact or if off-design flows are to be studied. A series of recommendations and guidelines for the CFD modelling of steam turbine exhaust hood flows based on this work are supplied. Experimental validation of the Durham Stage and Exhaust Hood Test Case and a comparison of full unsteady studies with the NLH method should be the next steps in this research.

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