This paper describes the unsteady force acting on steam turbine buckets which is induced by a potential field and a wake. A new method is proposed that can separate a potential field interaction and a wake interaction from the unsteady viscous flow computation. The new method does two computations for one model to get inviscid and viscous flow solutions. Then the quantitative effects of the factors that influence the unsteady force acting on the turbine buckets are clarified. The nozzle-bucket axial gap length is adopted for the factor to be studied and the proposed method is used to calculate the unsteady force of the bucket sections with different bucket heights in the same stage. The simple relationships between the nozzle-bucket axial gap length and the unsteady force are found to give easy and reliable prediction of the force.

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Reduced exhaust loss by an increase in the exhaust annulus area improves the thermal efficiency of steam turbines, such as 1000MW-class turbines. To cut this loss, the 3600rpm-50inch and 3000rpm-60inch last stage blades have been developed, getting one of the world’s largest exhaust annulus areas in the turbines. Three main problems are associated with long blades: large centrifugal stress, high Mach number flow, and low rigidity. To reduce the centrifugal stress, titanium alloy was applied for the blade material; it has higher specific strength than steel. Turbulent flow analyses were utilized to clarify the complex flow phenomena including shock waves. Variations in the flow passage area formed between blades were designed in accordance with Mach number which minimized losses caused by shock waves. The continuous covered blade structure, in which blades are interconnected with shroud covers at the tip and tie-bosses at the mid-span, increased the rigidity and vibrational damping.

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This paper explores the effect of a prescribed intense shear flow on the flow structures in an axial flow compressor cascade. An approximate shear flow is generated in the test section of an open circuit cascade wind tunnel by using a planar grid of parallel rods with varying solidity. To study only the effect of shear, a compressor cascade based on NACA65 series with a relatively low camber was chosen. The cascade was analysed experimentally as well as computationally (using ANSYS Fluent). The computational results of the cascade were compared with the available measured data. The results agreed well with the experimental data. Detailed analysis of the numerical results was then carried out to explore the complex flow features caused by the shear flow in a cascade. With uniform flow, the secondary flow was found to be negligible from experiments as well as from the computations. Therefore, in an attempt to amplify secondary flow, a shear flow generator was placed upstream of the cascade. Experiments showed quite contrasting results with shear flow, as compared to the uniform flow, in terms of the wake loss. Numerical analysis revealed the formation of vortices in the wake of the cascade due to secondary flows caused by the incoming shear flow and other interesting flow features.

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