fluid_mechanics

12 T urbomachines
CHAPTER OPENING PHOTO: A mixed-flow, transonic compressor stage. (Photograph courtesy of Concepts
NREC.)
Learning Objectives
After completing this chapter, you should be able to:
■ explain how and why a turbomachine works.
■ know the basic differences between a turbine and a pump.
■ recognize the importance of minimizing loss in a turbomachine.
■ select an appropriate class of turbomachine for a particular application.
■ understand why turbomachine blades are shaped like they are.
■ appreciate the basic fundamentals of sensibly scaling turbomachines that are
larger or smaller than a prototype.
■ move on to more advanced engineering work involving the fluid mechanics of
turbomachinery (e.g., design, development, research).
Turbomachines are
dynamic fluid machines
that add (for
pumps) or extract
(for turbines) flow
energy.
In previous chapters we often used generic “black boxes” to represent fluid machines such as pumps
or turbines. The purpose of this chapter is to understand the fluid mechanics of these devices when
they are turbomachines.
Pumps and turbines 1often turbomachines2 occur in a wide variety of configurations. In general,
pumps add energy to the fluid—they do work on the fluid to move and/or increase the pressure
of the fluid; turbines extract energy from the fluid—the fluid does work on them. The term
“pump” will be used to generically refer to all pumping machines, including pumps, fans, blowers,
and compressors.
Turbomachines involve a collection of blades, buckets, flow channels, or passages arranged
around an axis of rotation to form a rotor. A fluid that is moving can force rotation and produce
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