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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Gas Thermodynamic Properties<br />

<strong>Turbomachinery</strong> performance is also very dependent on the working fluid<br />

gas properties, including molecular weight and specific heat ratios. Several<br />

operational situations that can impact gas thermodynamic properties<br />

include the reingestion <strong>of</strong> hot exhaust gases, gun gas ingestion rocket<br />

exhaust ingestion, and operations in a high-humidity environment.<br />

Performance consequences include changes in specific heat ratios that can<br />

readily impact compressible flow properties, which include the local speed <strong>of</strong><br />

sound.<br />

Transient Operations<br />

Typical turbomachinery performance maps do not include transient<br />

operating characteristics. Performance maps are generated assuming steady<br />

flow conditions with the mechanical hardware in thermal equilibrium.<br />

TEST METHODOLOGY<br />

Testing Approach<br />

An approach that one might follow in defining and planning for a<br />

turbomachine component test is briefly described. The first step in test<br />

planning is that <strong>of</strong> defining the performance parameters that must be<br />

measured to satisfy the test objectives. Specific instrumentation required to<br />

record performance should also be specified.<br />

In addition, one must specify both the speed and flow ranges required<br />

for the test. The engineer must select a facility that both meets geometric<br />

interface requirements and is capable <strong>of</strong> operating over the flow and speed<br />

ranges required for the performance test. Once the test facility has been<br />

selected and the required performance data specified, the test rig design<br />

can be accomplished. Normally, test rigs are designed using full-scale<br />

hardware with the rotor turning at the design speed and with full-scale flow<br />

rates.<br />

However, successful testing can be accomplished with scaled test rigs.<br />

Scaling requirements include maintaining flow similarity between the full<br />

and scaled hardware. Reynolds number, Mach number, and characteristic<br />

geometric relationships must be maintained. The operating conditions<br />

within the stage must be dynamically similar, with the respective blade<br />

velocity triangles preserved. Classical scaling parameters for turbomachinery<br />

blading are defined in Ref. [9].<br />

Copyright © 2003 Marcel Dekker, Inc.

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