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Handbook of Turbomachinery Second Edition Revised - Ventech!

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classification is based on the direction <strong>of</strong> the flowing fluid in the runner.<br />

Based on this criterion, a turbomachine could be classified as an axial-flow,<br />

radial-flow, or mixed-flow machine. Examples <strong>of</strong> axial-flow machines are<br />

Kaplan turbines and axial-flow fans or blowers. A centrifugal pump and<br />

Francis turbine are examples <strong>of</strong> radial-flow machines. It should be noted<br />

that due to the complex flow passage <strong>of</strong> a turbomachine, there is no clear<br />

delineation between the types <strong>of</strong> machines in terms <strong>of</strong> direction <strong>of</strong> flow.<br />

Although the Kaplan turbine is classified as an axial-flow turbine, the fluid<br />

does have some radial velocity in it. The same comment applies to other<br />

machines, too. Thus, when one refers to an axial-flow machine, the<br />

implication is that the flow is predominantly in the axial direction. Yet<br />

another way <strong>of</strong> classifying turbomachines is based on the nature <strong>of</strong> the<br />

working fluid, whether it is compressible or incompressible. Examples <strong>of</strong> the<br />

former are various types <strong>of</strong> steam and gas turbines, compressors, and so<br />

forth, while all types <strong>of</strong> hydraulic turbines, pumps, low-speed blowers, and<br />

fans belong to the latter category.<br />

This chapter deals with hydraulic turbines, their common features,<br />

their operating characteristics, design features, differences, and so forth.<br />

Before these aspects are discussed in detail, the underlying unifying features<br />

<strong>of</strong> turbomachines like dimensional analysis, performance characteristics,<br />

and Euler turbine equations must be studied. In the rest <strong>of</strong> the chapter the<br />

various nondimensional groups <strong>of</strong> hydraulic machines are derived followed<br />

by the Euler turbine equation derivation, and the performance <strong>of</strong> different<br />

hydraulic turbines is discussed in detail. It should be pointed out that among<br />

the pertinent features in the discussion <strong>of</strong> hydraulic turbines and their<br />

mechanical characteristics are cost estimates, availability and use <strong>of</strong> water<br />

resources, and selection <strong>of</strong> various units. These are not discussed in this<br />

chapter, and the reader is referred to excellent references on such subjects by<br />

Fritz [1], Walters and Bates [2], and Warnick et al. [3].<br />

DIMENSIONAL ANALYSIS OF HYDRAULIC TURBINES<br />

For any hydraulic machine, it is <strong>of</strong> interest to obtain a relationship between<br />

head (specific energy or pressure), flow rate, power, torque, and so on with<br />

size, speed, and fluid properties. Some <strong>of</strong> the important variables are the<br />

flow rate Q, specific energy E, power P, speed N, a characteristic dimension<br />

D for size, density r, and viscosity m. The dimensions <strong>of</strong> the variables are<br />

given in Table 1.<br />

Copyright © 2003 Marcel Dekker, Inc.

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