Wind-energy generator farm, Altamont Pass, Cali-
fornia. Windmills have been used for power for
more than two thousand years. These multi-bladed
horizontal-axis wind turbines (HAWT’s) are
among the most efficient of windpower designs, as
discussed in this chapter. (Courtesy of Kevin
Schafer/Peter Arnold, Inc.)
11.1 Introduction and
Motivation. The most common practical engineering application for fluid mechanics
is the design of fluid machinery. The most numerous types are machines which add
energy to the fluid (the pump family), but also important are those which extract en-
ergy (turbines). Both types are usually connected to a rotating shaft, hence the name
The purpose of this chapter is to make elementary engineering estimates of the per-
formance of fluid machines. The emphasis will be upon nearly incompressible flow,
i.e., liquids or low-velocity gases. Basic flow principles are discussed, but not the de-
tailed construction of the machine.
Turbomachines divide naturally into those which add energy (pumps) and those which
extract energy (turbines). The prefix turbo- is a Latin word meaning “spin’’ or “whirl,’’
appropriate for rotating devices.
The pump is the oldest fluid-energy-transfer device known. At least two designs
date before Christ: (1) the undershot-bucket waterwheels, or norias, used in Asia and
Africa (1000 B.C.) and (2) Archimedes’ screw pump (250 B.C.), still being manufac-
tured today to handle solid-liquid mixtures. Paddlewheel turbines were used by the Ro-
mans in 70 B.C., and Babylonian windmills date back to 700 B.C. .
Machines which deliver liquids are simply called pumps, but if gases are involved,
three different terms are in use, depending upon the pressure rise achieved. If the pres-
sure rise is very small (a few inches of water), a gas pump is called a fan; up to 1 atm,
it is usually called a blower; and above 1 atm it is commonly termed a compressor.
There are two basic types of pumps: positive-displacement and dynamic or momentum-