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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 11 Schematic diagram <strong>of</strong> Kaplan turbine.<br />

The design methodology for propeller turbines proceeds along the<br />

same lines as a Francis turbine. There are, however, some important<br />

differences, the most important being the value <strong>of</strong> f, the speed ratio. While<br />

this value was low for Francis turbines, it can be as high as 1.5–2.5 for<br />

propeller turbines. The ratio <strong>of</strong> hub diameter to blade diameter, d/D, isa<br />

very important parameter in propeller turbines. Some variations <strong>of</strong> head,<br />

specific speeds, d=D, and number <strong>of</strong> blades for axial-flow turbines are shown<br />

in Table 3.<br />

The volumetric flow <strong>of</strong> water is given by the expression<br />

Q¼pðD 2<br />

d 2 ÞVax=4 ¼ðp=4ÞðD 2<br />

d 2 Þcð2gHÞ 1=2<br />

with the flow ratio c being in the range 0.35–0.75.<br />

An important feature <strong>of</strong> axial-flow turbines is that the blade speed<br />

varies along the blade, and hence the blade angle b also varies from point to<br />

Copyright © 2003 Marcel Dekker, Inc.<br />

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