Handbook of Turbomachinery Second Edition Revised - Ventech!

e predicted in advance. Total pressure probes and hot-wire anemometers
having very fast time responses overcome this difficulty and thus are
invaluable diagnostic tools. Laser anemometry is frequently used for this
purpose also.
O’Brien and Boyer [42] discusses some of the equipment and
procedures that have been used to examine the internal behavior of the
gas flow. Procedures used in other diagnostic tests and the results obtained
are described in O’Brien and Boyer [42], Ostdiek et al. [43], Budinger and
Thomson [44], and Budinger [45]. Chapters XI and XII of Ref. [1] provide
additional information. More information and additional references are
given in Lakshminarayana [2] and Serovy [3]. The examples cited describe
good diagnostic test procedures.
When there is a problem of locating the stages responsible for stall and
surge, one may be guided by an analysis of the overall performance data.
The variation of the ratio ðW ffiffiffiffi p pffiffiffiffi T=PÞ=½U=ðN
TÞŠ
with rotating speed
provides a measure of how the relative inlet air angles of the initial blade
rows change with speed. This ratio is proportional to the flow coefficient,
Vz;1=U. When it is divided by the quantity ðP2=P1Þ=ðT2=T1Þ, one obtains a
corresponding measure of Vz;2=U and the relative air angles in the final
blade rows. Selecting approximate values of P and T for the divisor enables
one to appraise the situation at intermediate stages. An example for air is
given by Table 3. (The numbers in the first two columns indicate the percent
of design value, while those in the last two columns are proportional to the
actual values.)
The low and nearly identical values under Vz;1=U at the two lowest
rotor speeds are an indication that the initial stages were stalling and were
responsible for the incidence of surge at these speeds. The same type of
Table 3
Stages
Effect of Speed on Value of Flow Coefficients, at Stall, of First and Last
N W ffiffiffiffi p
T=P
P2=P1 T2=T1 Vz;1=U Vz;2=U
0.5 8.7 1.8 1.26 17.4 12.2
0.6 10.8 2.5 1.40 17.2 10.1
0.7 13.5 3.5 1.57 19.3 8.7
0.75 15.0 4.05 1.66 20.0 8.2
0.8 18.0 5.0 1.74 22.5 7.9
0.9 25.4 7.6 1.98 28.2 7.4
1.0 33.6 9.8 2.10 33.6 7.1
Copyright © 2003 Marcel Dekker, Inc.