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Turbine Aerodynamics: Axial-Flow and Radial-Flow Turbine Design and Analysis
Ronald H. Aungier
Ronald H. Aungier
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ASME Press
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An aerodynamic performance analysis is essential for nearly all aspects of radial-inflow turbine aerodynamic design and application. The highly complex three-dimensional flow fields in these machines are strongly influenced by viscous effects and passage curvature. In contrast to the axial-flow turbine, the most effective approach to the performance analysis of radial-inflow turbine is the one-dimensional or mean-line method. Indeed, there is a close parallel with compressor performance analysis where the one-dimensional method is the most effective technique for the centrifugal compressor [1] but the more general hub-to-shroud flow method is the better choice for the axial-flow compressor [2].

One-dimensional performance analysis relies on analysis of the flow along a mean stream surface through various stage components. This approach is quite effective, but also has definite limitations. There are really an infinite number of ways a component can be designed to produce the specific geometrical parameters used by a one-dimensional performance analysis. The best a one-dimensional analysis can do is to predict the expected performance assuming the detailed geometry is based on “good design practice.” Obviously, good design practice is a relative term. In the case of the diffusing flows in compressors, this can result in significant uncertainty, particularly when analyzing older designs. It is a much less serious issue for turbines, where the accelerating flow results in less sensitivity to local flow behavior.

The literature includes a number of investigations into the performance analysis of radial-inflow turbines [67, 68, 75–83]. But unlike other popular turbomachinery types, the literature really doesn't provide any comprehensive and well-validated performance prediction systems for these machines. The axial-flow turbine performance analysis of chapters 4 and 5 is based on several well-developed and competing systems for modeling the loss and fluid turning. This writer's performance analyses for centrifugal and axial-flow compressors [1, 2] are based on similar well-developed technology from the open literature. In contrast, the empirical models presented in this chapter are largely unique. Some axial-flow turbine and centrifugal compressor models were adaptable to the radial-inflow turbine application, but most models were formulated specifically for this aerodynamic performance analysis. Although the open literature is quite limited, there are a number of proprietary performance analyses for radial-inflow turbines that appear to be well developed and effective. Indeed, some of these are implemented in commercially available software systems.

9.1 Radial-Inflow Turbine Stage Geometry
9.2 Boundary Layer Analysis
9.3 The Boundary Layer Loss Coefficient
9.4 Inlet Volute Analysis
9.5 Nozzle Row Analysis
9.6 Rotor Analysis
9.7 Vaneless Annular Passage Analysis
9.8 Exhaust Diffuser Analysis
9.9 Imposed Total Pressure Loss
9.10 Inlet Station Analysis
9.11 The Performance Analysis Strategy
9.12 Mass Balance Procedures
9.13 Subcritical Performance Analysis
9.14 Supercritical Performance Analysis
9.15 Typical Performance Analysis Results
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