Download 5li - CAV2012

Numerical Analysis for Influence of Cascade Solidity on the
Performances of Cavitating Inducers
Xiaojun Li
[email protected]
Research Center of Fluid Machinery Engineering and Technology, Jiangsu University, China
ABSTRACT
The main goal of this work is primarily a numerical simulation to provide useful information for the design of inducer. Performances of five inducers with
different cascade solidities at various flow rates were simulated by using software CFX. The steady flow simulation with cavitation model was carried out
to characterize and evaluate their performances under cavitating and non-cavitating conditions. An analysis of numerical result showed that there is an
evident change of pressure and efficiency in the inducer as the cascade solidity changes, the non-cavitating performance is little affected unless the cascade
solidity is less than 1.33. The best value of cascade solidity is of 2, and the rough recommended is about 1.7~2.5. The study also suggested that the increase
of cascade solidity appropriate makes it possible to improve cavitation performances.
GEOMETRICAL PARAMETERS AND DISCUSSION OF INDUCER I2
The inducer named I2 is designed for rated operational conditions corresponding to a flow coefficient of 0.123, a rotational speed of 2900 rpm and a
pressure coefficient of 0.127.
Blade number
3
Cascade solidity at tip
2
Axial length at hub
0.2
0.25
0.2
0.16
0.15
0.12
45mm
Tip diameter
64mm
Tip clearance
0.5mm
0.1
0.25
0.05
Hub-to-tip radio


0.08
Numerical
Radius of leading edge
18.7mm
Blade thickness
1.5mm
0
0.04
Table 1 Design Characteristics of Inducer
Figure 1 Model of Inducer
0.04
Experimental
0
0.07
0.1
1
0.13
0.16
0
0.19
Figure 2 Non-cavitating head coefficients
φnum=0.089
φexp=0.089
φnum=0.123
φexp=0.123
φnum=0.156
φexp=0.156
0.2
0.4
0.6

0.8
Figure 3 Cavitating head-drop curves
The other four inducers that have different cascade solidities were obtained by changing the axial length, and noted as I0.67, I1.33, I2.67 and I3.34,
respectively. The original inducer is expressed as I2 and the numbers indicate the cascade solidity of inducers.
OVERALL PERFORMANCES IN NON-CAVITATING REGIME FOR FIVE INDUCERS
For the values corresponding to the best efficiency, the flow coefficient and the head coefficient are given in Table 2. Inducer I1.33 has the best behavior
with a hydraulic efficiency of 56.65%. The efficiency at the best efficiency point reduces and the maximum point is moved to a smaller flow rate as the
cascade solidity increased.
φ=0.06
φ=0.089
φ=0.11
0.67
ψ
2
2.67
3.34
0.25
60%
0.2
50%
ηmax
φ1
0.67
56.64%
0.145
0.077
1.33
56.65%
0.133
0.104
2
54.3%
0.123
0.127
0.1
2.67
51.4%
0.117
0.136
0.05
3.34
49.13%
0.111
0.149
0.15
φ=0.133
φ=0.173
φ=0.145
2
3
0.2
0.16

30%
0.12

0
0.04 0.07
Table 2 Values of the flow coefficient and head
corresponding coefficient to the maximum efficiency
φ=0.123
φ=0.155
0.24
40%

Cascade solidity
1.33
0.1

20%
0.08
10%
0.04
0%
0.13 0.16 0.19
0
0.5
Figure 4 Overall performance in non-cavitating
regime for inducers
1
1.5
2.5

3.5
Figure 5 The relationship between cascade
solidities and pressure coefficient of inducers
BEHAVIOR OF CAVITATION
The numerical head drop curves are presented in Fig.6 for the four inducers at seven flow rates. For the inducers I0.67 and I1.33, around the rated flow
rate and higher flow rates, the head curves show a sudden drop. While the head curves of the other two inducers with larger cascade solidity show a
significant increase in pressure at the low flow rate.
0.2
0.16
φ=0.089
φ=0.111
φ=0.123
φ=0.133
φ=0.145
φ=0.155
φ=0.164
0.12

0.2
0.2
0.2
0.16
0.16
0.16
0.12
0.12
0.12


0.08
0.08
0.04
0.04
0
0
0
0.2
0.4
0.6

0.8

0.08
φ=0.097
φ=0.133
φ=0.164
0
0.2
Inducer I0.67
φ=0.111
φ=0.145
0.08
0.04
φ=0.123
φ=0.155
φ=0.089
φ=0.133
φ=0.164
0
0.4
0.6

0
0.8
0.2
Inducer I1.33

φ=0.111
φ=0.145
0.04
φ=0.123
φ=0.156
φ=0.089
φ=0.133
φ=0.164
0
0.4
0.6
0
0.8
0.2
Inducer I2
φ=0.111
φ=0.145
0.4
φ=0.123
φ=0.155
0.6

0.8
Inducer I2.67
Figure 6 Head-drop curves in cavitating regime for inducer I0.67 to I2.67
The behavior in cavitating regime is characterized by cavitation numbers corresponding to head drops of 3%, 5%, 8%, 10% and 15% shown in Fig.7. It
can be found in these figures that the increase of cascade solidity appropriate makes it possible to improve the cavitation performances, with the increase of
cascade solidity, the corresponding critical cavitation number decreases.
0.16
0.16
0.12
0.12
0.08
0.08


3%
5%
8%
10%
0.1
0.12
0.14
0.12

0.08
3%
5%
8%
10%
15%
0.12

0.08
0.04
0.04
0.16
0.18
0
0.08
0.1
0.12
1
Inducer I0.67
3%
5%
8%
10%
15%
15%
0
0.08
3%
5%
8%
10%
15%
0.04
0.04
0.16
0.16
Inducer I1.33
1
0.14
0.16
0.18
0
0.08
0.1
0.12
1
0.14
0.16
Inducer I2
0.18
0
0.08
0.1
0.12
1
0.14
0.16
0.18
Inducer I2.67
Figure 7 Cascade solidity influence on the performance in a regime of cavitation
CONCLUSION
The comparison of the five inducers shows an optimal value of cascade solidity. Inducer I0.67 has the worst cavitation performance, while inducer I3.34
makes the most hydraulic loss. So it is better to select the cascade solidity around 2, the rough recommended is about 1.7~2.5 in this paper. One also
observes the increase of cascade solidity appropriate makes it possible to improve the cavitation performance.