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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 15 Wake rake total pressure pr<strong>of</strong>ile.<br />

this measurement. In addition, the pr<strong>of</strong>iles can be integrated to give very<br />

accurate flow-field properties at the measurement plane.<br />

Rotor Wheel Speeds<br />

Test rig rotor stage rotational speeds must be accurately determined at each<br />

operating point during the test. Rotational speed can be measured with a<br />

magnetic pulse generator or a photoelectric sensor in conjunction with a<br />

geared tooth mounted on the drive shaft. Data are normally transmitted to a<br />

frequency counter calibrated to read rpm directly.<br />

Torque Measurements<br />

A torque meter can be used to measure the power required to drive the test<br />

rig or, in the case <strong>of</strong> a turbine rig, the power generated. Included in the<br />

torque meter measurement are both stage aerodynamic power and the<br />

mechanical power required to overcome drive system losses from bearings<br />

and windage. The power utilization due to aerodynamic work must be<br />

separated from the mechanical power losses for accurate performance<br />

measurements. The torque meter typically includes a calibrated strain gauge<br />

element bonded to the drive shaft. The measured torque and shaft rotational<br />

speed are used to calculate power.<br />

Copyright © 2003 Marcel Dekker, Inc.

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