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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Corrected Flow<br />

The flow rates used for performance map presentation are corrected using<br />

the following expressions:<br />

pffiffi<br />

_m y<br />

_mcorr ¼<br />

d<br />

y ¼ TTin<br />

Tref<br />

d ¼ PTin<br />

Pref<br />

where _m is the measured flow rate and y and d are, respectively, the<br />

temperature and pressure ratios discussed earlier. Corrected mass flow rate<br />

can be equated to the stage inlet Mach number.<br />

Corrected Speed<br />

Rotor blade speeds are corrected to standard conditions using this equation:<br />

Ncorr ¼ N pffiffiffi<br />

y<br />

where N is the physical speed. The corrected speed is related to the rotor<br />

blade tip Mach number.<br />

Performance Parameters<br />

The following expressions are typical <strong>of</strong> those used to calculate turbomachine<br />

performance parameters. These expressions can be tailored to meet<br />

individual test and data presentation requirements.<br />

Bellmouth Flow Rate. Bellmouth measurements provide an accurate flow<br />

measurement technique without obstructing the flow-like venturi meters,<br />

flow nozzles, or orifice plates. Bellmouth flow rates can be calculated with<br />

the following expression:<br />

_m ¼ðCdÞA<br />

ffiffiffiffi<br />

g<br />

R<br />

r PT<br />

p<br />

ffiffiffiffiffiffi<br />

TT<br />

sffiffiffiffiffiffiffiffiffiffi"<br />

2 P<br />

2=g<br />

P<br />

#<br />

ðgþ1Þ=g<br />

1=2<br />

g 1<br />

PT<br />

In this equation the static pressure is that measured downstream <strong>of</strong> the<br />

bellmouth, the total properties are either ambient test-cell properties or<br />

those measured in the flow path, and Cd is the discharge loss coefficient for<br />

the bellmouth. The area used for calculations is that <strong>of</strong> the duct cross section<br />

at the static pressure measurement plane. The static pressure taps are<br />

typically installed in a constant-area duct approximately one duct diameter<br />

downstream from the bellmouth.<br />

Copyright © 2003 Marcel Dekker, Inc.<br />

PT

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