Handbook of Turbomachinery Second Edition Revised - Ventech!

[27]. In order to avoid manufacturing problems at the rotor exit, we choose
11 full blades and 11 splitter blades, for a total of 22 blades at the rotor inlet.
We now recalculate the ratio of absolute rotor inlet tangential velocity to the
wheel speed from Eq. (61):
Vy1
U1
¼ 1
2
¼ 0:9091
22
From Eq. (9) we calculate the required wheel speed:
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
DhOA
32:174
ZC
U1 ¼
¼
Vy1=U1
lbm ft
lbf sec2 ft lbf 778:16 Btu 43:97 Btu
v
u
t
lbm
0:9091
¼ 1100 ft= sec
As a check, we recalculate the blade-jet speed ratio:
U1
C0
¼
1100 ft= sec
¼ 0:7015
1569 ft= sec
which is very close to our original intent. The absolute tangential velocity at
rotor inlet is
Vy1 ¼ Vy1
U1
U1 ¼ð0:9091Þð1100 ft= secÞ ¼1000 ft= sec
Next, we specify an inlet absolute flow angle of 758 from the radial
direction. We can now calculate the remainder of the inlet velocity triangle,
the results of which appear in Fig. 18. To determine the rotor inlet blade
height, we will need the rotor inlet density. From the vector diagram of Fig.
18, the value of the rotor inlet absolute velocity, V1, is 1036 ft/sec. The inlet
critical velocity is
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2ð1:4Þ ft lbf
acr1 ¼
32:174
1 þ 1:4 lbm sec2 s
ft lbf
53:34 760 R
lbm R
¼ 1234 ft= sec
The rotor inlet density is determined (assuming a 2% inlet and stator
total pressure loss) from
r 1 ¼ p0 1
RgasT 0 1
1
¼0:1123 lbm=ft 3
" # 1=ðg 1Þ
g 1
g þ 1
V1
acr1
Copyright © 2003 Marcel Dekker, Inc.
2
¼ ð0:98Þð44:1 psiaÞð144 in2 =ft 2 Þ
ð53:34 ft lbf =lbm RÞð760 RÞ 1
" # 2:5
1
6
1036
1234
2