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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 12 Sketch <strong>of</strong> flow surface and streamlines when assumed flow lies on the<br />

surface <strong>of</strong> a right circular cylinder.<br />

Equations (13a), (13b), and (13c) express the components <strong>of</strong> vorticity in the<br />

radial, axial, and circumferential directions, respectively:<br />

V<br />

r<br />

qVz<br />

rqy<br />

qðrVyÞ<br />

qr<br />

qVr<br />

qz<br />

qVy<br />

qz ¼ zr ð13aÞ<br />

qVr<br />

¼ zz<br />

Vqy<br />

ð13bÞ<br />

qVz<br />

qr ¼ zy ð13cÞ<br />

The values <strong>of</strong> Vr and its derivatives vanish under our assumptions. If the<br />

assumed inviscid flow upstream <strong>of</strong> a blade row has no radial component <strong>of</strong><br />

vorticity, then this condition must prevail throughout the blade row. The<br />

right-hand side <strong>of</strong> Eq. (13a) is thus 0. [The significance <strong>of</strong> the right-hand side<br />

<strong>of</strong> Eqs. (13b) and (13c) is discussed later.]<br />

Two-Dimensional Cascades<br />

Inasmuch as r is assumed to be constant on any stream surface, the<br />

equations may be altered so that dz ¼ dx and rdy ¼ dy. Hence, Eqs. (12)<br />

Copyright © 2003 Marcel Dekker, Inc.

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