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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Ambient Conditions<br />

In addition to test rig instrumentation and measurements, an accurate<br />

measurement <strong>of</strong> the local ambient conditions must be made during the test<br />

activity. These measurements include barometric pressure, ambient temperature,<br />

relative humidity, and wind speed and direction if testing is<br />

accomplished outside in an unprotected area. If the test rig is installed inside<br />

a closed test cell, test-cell static pressure should be recorded.<br />

TEST HARDWARE<br />

Test hardware, commonly referred to as ‘‘test rigs,’’ is designed to simulate<br />

flow and operating conditions found in the turbomachine stage <strong>of</strong> interest.<br />

Great care must be taken to duplicate the flow path and blading as close as<br />

possible to the stage that is being simulated. Test rigs are normally designed<br />

so that a complete range <strong>of</strong> performance data can be measured. This implies<br />

that the rotor blade speeds be variable and that the stage pressure ratios be<br />

controlled with a type <strong>of</strong> flow resistance such as a throttle valve.<br />

The test facility must have the power capacity and speed range to<br />

operate the test rig over the operating conditions required for performance<br />

testing. In addition, the test hardware must be designed to accommodate the<br />

instrumentation required for the test activity. Test stage flow properties<br />

must be duplicated as closely as possible to those <strong>of</strong> the component <strong>of</strong><br />

interest in the gas turbine.<br />

A schematic <strong>of</strong> a typical test rig for fan and compressor test activities is<br />

seen in Fig. 18. Test rig components include avariable-speed drive system,<br />

inlet and discharge ducting, a control valve, flow-measuring hardware, and<br />

the test stage <strong>of</strong> interest.<br />

Normally an aerodynamically contoured bellmouth is used for the test<br />

rig air inlet. The bellmouth shape should have a large radius to minimize<br />

localized high-velocity areas and to produce a uniform inlet flow. The<br />

bellmouth can also be used as an accurate flow-measuring device. Other<br />

flow-measuring devices typically used in rig testing are venturi meters, flow<br />

nozzles, and sharp-edge orifice plates. Flow-measuring devices must be sized<br />

for given flow ranges to ensure that measurement accuracies are maintained.<br />

Because <strong>of</strong> the broad range <strong>of</strong> air flows required for most performance<br />

testing, it is <strong>of</strong>ten necessary to change the size <strong>of</strong> the flow-measuring device<br />

so that it will be operating at its most sensitive flow range for that part <strong>of</strong> the<br />

test.<br />

Some test rigs include an inlet plenum chamber upstream <strong>of</strong> the test rig<br />

inlet plane. The chamber is normally several diameters larger than the flow<br />

Copyright © 2003 Marcel Dekker, Inc.

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