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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Mach number at a compressor outlet is inherently prescribed by the<br />

intended use <strong>of</strong> the unit.<br />

Relative Mach Number<br />

Figure 11(a) is a typical diagram <strong>of</strong> the velocity vectors at the tip <strong>of</strong> a rotor<br />

blade. Note that inlet velocity is assumed to be axial. Figure 11(b) presents<br />

the case when the inlet flow has a tangential component. Both the gas<br />

velocity and Mach number relative to the moving blades are determined by<br />

the selections <strong>of</strong> the inlet Mach number and the blade speed. As a rule,<br />

relative Mach numbers up to about 1.3 may be routinely accepted if the<br />

blades are thin. Higher relative Mach numbers can be used effectively, but<br />

extra considerations are necessary, as noted later.<br />

Figure 11 Velocity diagram <strong>of</strong> typical stages: (a) axial velocity ahead <strong>of</strong> rotor, (b)<br />

rotating flow ahead <strong>of</strong> rotor. OA: absolute inlet velocity, OB: relative inlet velocity<br />

for rotor, OC: relative exit velocity for rotor, OD: relative inlet velocity for stator,<br />

OE: relative exit velocity for stator.<br />

Copyright © 2003 Marcel Dekker, Inc.

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