A computational study has been performed to investigate the effects of blade row interaction on the performance of radial turbomachines, which was motivated by the need to improve our understanding of the blade row interaction phenomena for further improvement in the performance. High-speed centrifugal compressor stages with three settings of radial gap are configured and simulated using a three-dimensional Navier-Stokes flow method in order to investigate the impact of blade row interaction on stage efficiency. The performance predictions show that the efficiency deteriorates if the gap between blade rows is reduced to intensify blade row interaction, which is in contradiction to the general trend for stage axial compressors, hi the compressors tested, the wake chopping by diffuser vanes, which usually benefits efficiency in axial compressor stages, causes unfavourable wake compression through the diffuser passages to deteriorate the efficiency. Similarly, hydraulic turbine stages with three settings of radial gap are simulated numerically. A new three-dimensional Navier-Stokes flow method based upon the dual-time stepping technique combined with the pseudo-compressibility method has been developed for hydraulic flow simulations. This method is validated extensively with several test cases where analytical and experimental data are available, including a centrifugal pump case with blade row interaction. Some numerical tests are conducted to examine the dependency of the flow solutions on several numerical parameters, which serve to justify the sensitivity of the solutions. Then, the method is applied to performance predictions of the hydraulic turbine stages. The numerical performance predictions for the turbines show that, by reducing the radial gap, the loss generation in the nozzle increases, which has a decisive influence on stage efficiency. The blade surface boundary layer loss and wake flow mixing loss, enhanced with a higher level of flow velocity around blading and the potential flow disturbances, are responsible for the observed trend.

The flow in multistage axial flow compressors is particularly complex in nature because of the proximity of moving bladerows, the growth of end-wall boundary layers and the presence of tip and seal leakages and secondary flow. The problems associated with these phenomena are at their most acute in the latter, subsonic stages of the core compressor, where Reynolds numbers are modest and the blading has low aspect ratio. Indeed, much of the inefficiency of axial stages is believed to be associated with the interaction between blading and end-wall flows. The fact that the end-wall flow phenomena result in conditions local to the blade which are quite different from those over the major part of the annulus was appreciated by many of the earliest workers in the axial turbomachinery field. However, experiments on blading designs aimed specifically at attacking the end-loss have been sparse. This thesis includes results from tests of conventional and end-bent blading in a four-stage, low-speed, axial compressor, built specifically for the task, at a scale where high spatial measurement resolution could be readily achieved within the flowpath. Two basic design styles are considered: a zero a0 stage with DCA aerofoils and a low-reaction controlled-diffusion design with cantilevered stators. The data gives insight into the flow phenomena present in 'buried' stages and has resulted in a much clearer understanding of the behaviour of end-bent blading. A 3D Navier-Stokes solver was calibrated on the two low-reaction stators and was found to give good agreement with most aspects of the experimental results. An improved design procedure is suggested based on the incorporation of end-bends into the throughflow and iterative use of the 3D Navier-Stokes solver.

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Airworthiness certification of commercial transport aircraft requires a safety analysis of the propulsion system to establish that the probability of a failure jeopardising the safety of the aeroplane is acceptably low. The needs and desired features of such a propulsion system safety analysis are discussed, and current techniques and assumptions employed in such analyses are evaluated. It is concluded that current assumptions and techniques are not well suited to predicting behaviour of the propulsion system in service. The propulsion accident history of the high bypass ratio commercial transport fleet is reviewed and an alternate approach to propulsion system safety analysis is developed, based on this accident history. Features of the alternate approach include quantified prediction of propulsion related crew error, engine-level reliability growth modelling to realistically predict engine failure rates, and quantified credit for design features which mitigate the effects of propulsion system failures. The alternate approach is validated by applying it to two existing propulsion systems. It is found to produce forecasts in good agreement with service experience. Use of the alternate approach to propulsion system safety analysis during design and development will enable accurate prediction of the expected propulsion related accident rate and identification of opportunities to reduce the accident rate by incorporating mitigating features into the propulsion system/aeroplane design.

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