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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 19 Downstream resistance.<br />

and compressor rigs where the performance is so sensitive to rotor blade<br />

speed. Downstream resistance is then increased by closing a throttle valve or<br />

partially blocking the discharge with screens. The test stage responds by<br />

pumping at a higher pressure to match the increased downstream losses. The<br />

performance data are once again recorded.<br />

This process is continuously repeated until stall or surge is detected.<br />

Safety dictates that test rigs not be operated in a surge or stall operating<br />

condition. The stall line is defined by recording a performance point as close<br />

to stall as possible without stall actually occurring. At all operating<br />

conditions, data points should not be recorded until the test rig has achieved<br />

thermal equilibrium. The complete process is repeated for different rotor<br />

blade speeds until the desired performance map has been generated.<br />

Turbine test rigs require a high-temperature and -pressure air supply<br />

to drive the stage. The resultant turbine power is absorbed by a<br />

dynamometer coupled directly to the drive shaft. Turbine stage loading is<br />

varied by increasing or decreasing the resistance <strong>of</strong>fered by the dynamometer.<br />

Copyright © 2003 Marcel Dekker, Inc.

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