Book contents
- Frontmatter
- Contents
- Preface
- 1 Introduction to Gas-Turbine Engines
- 2 Overview of Turbomachinery Nomenclature
- 3 Aerothermodynamics of Turbomachines and Design-Related Topics
- 4 Energy Transfer between a Fluid and a Rotor
- 5 Dimensional Analysis, Maps, and Specific Speed
- 6 Radial-Equilibrium Theory
- 7 Polytropic (Small-Stage) Efficiency
- 8 Axial-Flow Turbines
- 9 Axial-Flow Compressors
- 10 Radial-Inflow Turbines
- 11 Centrifugal Compressors
- 12 Turbine-Compressor Matching
- References
- Index
11 - Centrifugal Compressors
Published online by Cambridge University Press: 05 September 2012
- Frontmatter
- Contents
- Preface
- 1 Introduction to Gas-Turbine Engines
- 2 Overview of Turbomachinery Nomenclature
- 3 Aerothermodynamics of Turbomachines and Design-Related Topics
- 4 Energy Transfer between a Fluid and a Rotor
- 5 Dimensional Analysis, Maps, and Specific Speed
- 6 Radial-Equilibrium Theory
- 7 Polytropic (Small-Stage) Efficiency
- 8 Axial-Flow Turbines
- 9 Axial-Flow Compressors
- 10 Radial-Inflow Turbines
- 11 Centrifugal Compressors
- 12 Turbine-Compressor Matching
- References
- Index
Summary
From a historical viewpoint, the centrifugal compressor configuration was developed and used well before axial-flow compressors, even in the propulsion field. The common belief that such a “bulky” compressor type, because of its large envelope and weight (Fig. 11.1), has no place except in ground applications is not exactly accurate. For example, with a typical total-to-total pressure ratio of, say, 5:1, it would take up to three axial-compressor stages to absorb similar amounts of shaft work that a single centrifugal compressor stage would. In fact, the added engine length, with so many axial stages, would increase the skin-friction drag on the engine exterior almost as much as the profile drag, which is a function of the frontal area.
Despite the preceding argument, the tradition remains that the centrifugalcompressor propulsion applications are unpopular. Exceptions to this rule include turboprop engines and short-mission turbofan engines, as shown in Figure 11.2.
An attractive feature of centrifugal compressors has to do with their off-design performance. Carefully designed, a centrifugal compressor will operate efficiently over a comparatively wider shaft speed range. This exclusive advantage helps alleviate some of the problems associated with the turbine-compressor matching within the gas generator.
One of the inherent drawbacks of centrifugal compressors has to do with multiple staging. As illustrated in Figure 2.12, the excessive 180 flow-turning angle of the annular return duct, in this case, will increase the flow rotationality (in terms of vorticity) and encourage the cross-stream secondary flow migration. This simply sets the stage for high magnitudes of total pressure loss and boundary-layer separation.
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- Principles of Turbomachinery in Air-Breathing Engines , pp. 471 - 528Publisher: Cambridge University PressPrint publication year: 2006