Chapter 11
Detailed Aerodynamic Design of Radial-Inflow Turbine Components


The nozzle-blade preliminary aerodynamic design procedure described in chapter 10 is easily modified to provide a sound basis for the detailed aerodynamic design also. That approach is almost always sufficient to achieve design objectives for both aerodynamic performance and mechanical integrity. Impeller detailed design is conveniently accomplished using procedures essentially identical to those commonly used for centrifugal compressors. Indeed, this writer uses the detailed design system described in Aungier [1] for both types of impellers. The only modification required to extend the centrifugal compressor impeller detailed design procedure to radial-inflow turbines was to include provision to reverse the geometry exported to aerodynamic analysis, applications such that the flow direction is reversed. Hence, the inlet becomes the discharge, and inversely, when the detailed geometry is reversed. This was simply a matter of convenience due to the fact that a sophisticated impeller gaspath design system already existed. Investigators developing this system specifically for radial-inflow turbines would normally avoid the need to reverse the geometry. Hence, the descriptions provided in this chapter address this problem in the turbine orientation. But it is appropriate to acknowledge the fact that the present description is really no different than the impeller gaspath design system described in [1].

The detailed design process really addresses design details that are largely ignored by the performance analysis of chapter 9 and the preliminary design system of chapter 10. Indeed, a fundamental assumption of the performance analysis is that the components have been designed consistent with good design practice. The limited geometry specified for the performance analysis can be produced by a wide variety of detailed component designs. Those specifications are by no means sufficient to ensure that the components will perform as predicted. That issue is addressed in the detailed design process by evaluating the internal flow produced by the design. This requires use of internal flow analysis procedures describe in subsequent chapters of this book. These include blade-to-blade flow analysis (chapter 13), quasi-three-dimensional flow analysis (chapter 14) and boundary layer analysis (chapters 13 and 14). In the present context, it is not necessary to be familiar with the theory behind the internal flow analyses of chapters 13 and 14. The objective of the detailed design process is to avoid excessive diffusion and flow separation along the blade surfaces and end-wall contours of the components. This objective is less challenging for the accelerating flow in turbines as compared to the diffusing flow in compressors. But is does remain a necessary step to achieving good aerodynamic performance.

  • 11.1 Nozzle Blade Detailed Design
  • 11.2 A General Approach to Gaspath Detailed Design
  • 11.3 Useful Curve Forms
  • 11.4 Constructing the Annulus and Quasi-Normals
  • 11.5 Constructing the Blade Camberline
  • 11.6 Constructing the Blade Surfaces
  • 11.7 The Blade Passage Throat Geometry
  • 11.8 An Effective Gaspath Design System
  • 11.9 Application to Impeller Design

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