Crack fault of a centrifugal impeller occurred while working. The finite element model of the impeller was established and vibrational characteristics were analyzed for to find the reason of the crack fault in this paper. The resonance frequencies of the impeller were identified with the help of Campbell diagrams. The modal experiments were carried out with hammering method, the modal parameters were obtained and the correct of the simulations was verified under the same constraints with the FEM model. Computation effort was saved while accuracy was retained making use of the cyclic symmetry technique in ANSYS. The results showed that simulating results agreed well with that of the experiments

Di Wang

Fei Wang

Guihuo Luo

English

Vibroengineering PROCEDIA

  © JVE INTERNATIONAL LTD. VIBROENGINEERING PROCEDIA. SEP 2015, VOLUME 5. ISSN 2345-0533 287 
Vibration characteristics analysis of a centrifugal 
impeller 
Di Wang1, Guihuo Luo2, Fei Wang3 
Nanjing University of Aeronautics and Astronautics, College of Energy and Power Engineering,  
Nanjing 210016, China 
2Corresponding author 
E-mail: 1348492161@qq.com, 2ghluo@nuaa.edu.cn, 3woaijuziyy@gmail.com 
(Accepted 4 September 2015) 
Abstract. Crack fault of a centrifugal impeller occurred while working. The finite element model 
of the impeller was established and vibrational characteristics were analyzed for to find the reason 
of the crack fault in this paper. The resonance frequencies of the impeller were identified with the 
help of Campbell diagrams. The modal experiments were carried out with hammering method, the 
modal parameters were obtained and the correct of the simulations was verified under the same 
constraints with the FEM model. Computation effort was saved while accuracy was retained 
making use of the cyclic symmetry technique in ANSYS. The results showed that simulating 
results agreed well with that of the experiments. 
Keywords: crack, vibrational characteristics, cyclic symmetry, modal analysis, resonance. 
1. Introduction 
The centrifugal impeller the axial flow compressor suffered enormous centrifugal and 
aerodynamic force under high-speed rotating. At the same time, workload and working 
environment of impeller were very complicated due to alternating load by vibration, corrosion and 
oxidation during working time. A crack fault occurred in the actual working was discussed about 
the impeller in this paper. Analysis results with fracture surface indicated a fatigue crack. Two 
possible reasons were preliminary speculated: resonance or forced vibration caused by the 
rectifying plate’s wake before the impeller [1-4]. The movement dynamics equations about the 
impeller of multiple degrees of freedom were written as: 
ܯݑሷ (ݐ) + ܥݑሶ (ݐ) + ܭݑ(ݐ) = ܯ߱ଶݎ + න ݂(ݐ)݀ܵ(ݕ)
ௌ
, (1)
where ܯݑሷ (ݐ) and ܥݑሶ (ݐ) are called as centrifugal force and aerodynamic force of blade surface, 
ܯ,  ܥ  and ܭ  as mass, damp and stiffness matrix respectively, ݑ(ݐ) , ݑሶ (ݐ)  and ݑሷ (ݐ)  mean 
displacement, velocity and acceleration respectively. ݂(ݐ) represent gas static pressure [5]. 
2. Simulation  
2.1. The finite element model 
The finite element model was established for the 1/16 of centrifugal impeller basing on actual 
centrifugal impeller structure. The vibration characteristic analysis was completed for whole of 
centrifugal impeller with cyclic symmetry method in this paper [5]. The impeller modals were 
calculated basing on the basic sectors with the help of large general structural analysis software 
ANSYS. The model was divided into 981522 elements and 192280 nodes and Solid 185 element 
was adopted in ANSYS. The inner diameter about front face and end face of the disk were 
constrained axially and circumferentially. The model about 3-D and grid of basic sector were 
shown as Fig. 1 [6]. 
VIBRATION CHARACTERISTICS ANALYSIS OF A CENTRIFUGAL IMPELLER.  
DI WANG, GUIHUO LUO, FEI WANG 
288 © JVE INTERNATIONAL LTD. VIBROENGINEERING PROCEDIA. SEP 2015, VOLUME 5. ISSN 2345-0533  
a) 3-D model
 
b) Grid of the basic sector
Fig. 1. Model 
2.2. Simulation results 
The Block-Lanczos method was applied to extract eigenvalues and eigenvectors. The natural 
frequencies changed as the rotating speed due to the rotating stiffening effect. The centrifugal 
force was applied by the prestress analysis in ANSYS to consider the rotating stiffening effect. 
Modal analysis were conducted under 700 rad/s, 1400 rad/s, 2100 rad/s, 2800 rad/s, 3500 rad/s, 
4200 rad/s, respectively. The results were listed according to the number of nodal diameter. 
Campbell diagrams were shown as Fig. 2. The horizontal axis was the rotational speed and the 
vertical axis was the natural frequency [7-10]. 
 
a) 0 nodal diameter
 
b) 1 nodal diameter
 
c) 2 nodal diameter
 
d) 3 nodal diameter
Fig. 2. Campbell diagram 
VIBRATION CHARACTERISTICS ANALYSIS OF A CENTRIFUGAL IMPELLER.  
DI WANG, GUIHUO LUO, FEI WANG 
 © JVE INTERNATIONAL LTD. VIBROENGINEERING PROCEDIA. SEP 2015, VOLUME 5. ISSN 2345-0533 289 
From the results of Campbell diagrams, there is no dangerous resonance frequency of 1ܺ while 
there are some dangerous resonance frequencies of 5ܺ. The dangerous frequencies occurred in the 
first natural frequencies of 0 nodal diameter and the second natural frequencies of 1 nodal diameter. 
The Fig. 2 showed that the discrepancy between resonance speed 34440 rpm and operating speed 
33550 rpm was 2.65 %. Corresponding mode shapes were similar to centrifugal impeller crack 
failure shape, shown as Fig. 3. 
a) Mode shape of 0 nodal diameter 
 
b) Mode shape of 1 nodal diameter 
Fig. 3. Mode shapes 
In addition, the common speeds operated on 20000 rpm (333.3 Hz, 2093.3 rad/s), 25000 rpm 
(416.7 Hz, 2612.5 rad/s), 32400 rpm (540 Hz, 3391.2 rad/s), 32900 rpm (548.3 Hz, 3443.5 rad/s), 
and 33550 rpm (559.2 Hz, 3511.6 rad/s) for the centrifugal impeller. According to Campbell 
diagram, first-order and second order of 0 nodal diameter resonant frequency occurred near by the 
21000 rpm and 24000 rpm respectively. At the same time, second-order of 1 nodal diameter 
resonance frequency occurred near by 34000 rpm. The extreme difficulties existed for to avoid 
the resonance frequency. These rotating speeds likely resulted in resonance. 
 
Fig. 4. Test mode 
3. Modal test and analysis 
The correctness of the calculation results were verified by the model analysis test with 
hammering method. Geometry model which needed to correspond with the transfer function was 
the basis of the modal animation display. The geometric structure figure, which had 208 geometric 
points, was shown as Fig. 4 for the impeller disk basing on experiment scheme. Every point should 
be measured at least 5 times and the measured mean value was used as the data of analyzing 
transfer function to improve the measuring accuracy in modal test. According to the defined 
geometric relations and directions of force, experimental data collection was completed under the 
VIBRATION CHARACTERISTICS ANALYSIS OF A CENTRIFUGAL IMPELLER.  
DI WANG, GUIHUO LUO, FEI WANG 
290 © JVE INTERNATIONAL LTD. VIBROENGINEERING PROCEDIA. SEP 2015, VOLUME 5. ISSN 2345-0533  
same constrained condition. Every point’s input force and output response signal was calculated 
under the analyzing window, which could get relevant transfer function. Frequency domain 
method was used in the process of modal fitting. Frequency and vibration mode comparison results 
were shown as Fig. 5 and Table 1. 
Table 1. The comparison of frequency 
Nodal diameter 1 2 3 
Test frequency (Hz) 1637 3479 4038 
Calculate frequency (Hz) 1792.1 3357 4003.3 
Error –8.6 % 3.6 % 7.6 % 
 
 
a) The comparison of test and theoretical mode shape about 1 nodal-diameter 
 
b) The comparison of test and theoretical mode shape about 2 nodal-diameter 
 
c) The comparison of test and theoretical mode shape about 3 nodal-diameter 
Fig. 5. The comparison of test modes and theoretical modes 
The errors of results between calculating and testing excited –8.6 %, 3.6 % and 7.6 % 
VIBRATION CHARACTERISTICS ANALYSIS OF A CENTRIFUGAL IMPELLER.  
DI WANG, GUIHUO LUO, FEI WANG 
 © JVE INTERNATIONAL LTD. VIBROENGINEERING PROCEDIA. SEP 2015, VOLUME 5. ISSN 2345-0533 291 
separately about the impeller in the static frequency condition from Table 1 and Fig. 5. The 
calculating accuracy was verified by the modal test for cyclic symmetry method applied FEM in 
ANSYS. 
4. Conclusions and future prospect 
Comparing difference between the dynamic characteristics analyzed exactly by cyclic 
symmetry technique and taking into consideration of rotating stiffening effect in ANSYS and 
modal testing in the paper, the reasons of the fault were concluded as followings. 
1) The resonance frequencies of the impeller were closed to multiple operating frequencies 
according to the Campbell diagrams. It was possible that the resonances occurred nearby the 
rotating speeds of 21000 rpm, 24000 rpm and 34000 rpm. Especially, the crack failure shape of 
the impeller was similar to the shape of the maximum strain position about second natural 
frequencies of 1 nodal diameter, it was possible to lead to fatigue crack failure if the impeller 
worked at above rotating speeds. 
2) The modal parameters and mode shapes obtained by modal test about static frequency were 
basically agreed with the simulating results under the same constraints. The accuracy of simulating 
method was verified. 
3) The impeller modals were extremely rich. To adjust the resonance frequencies were  
difficult. It was too hard to coordinate the contradiction between structure and frequency. 
Therefore, the vibration of the axial flow compressor should be closely monitored. 
4) On the foundation, the frequency spectrum would be analyzed in consideration of the forced 
vibration under the aerodynamic force of the rectifying plate. 
References 
[1] Chen Xiang, Zhu Jing, Zhang Ya Vibration characteristics analysis of blisk with cracking blades on 
axial flow compressor. Journal of Aerospace Power, Vol. 30, Issue 5, 2015, p. 1141-1148, 
(in Chinese). 
[2] Saito A., Castanier M. P., Pierre C. Effects of a cracked blade on mistuned turbine engine rotor 
vibration. Journal of Vibration and Acoustics, Vol. 131, Issue 6, 2009, p. 1-9. 
[3] Jin Xiangming, Gao Deping, Cai Xianxin, Wu Liqiang Analysis of integrated centrifugal impeller 
blade vibration reliability. Journal of Aerospace Power, Vol. 19, Issue 5, 2004, p. 610-613, (in 
Chinese). 
[4] Huang B. W. Effect of number of blades and distribution of cracks on vibration localization in a 
cracked pre-twisted blade system. International Journal of Mechanical Sciences, Vol. 48, Issue 1, 
2006, p. 1-10. 
[5] Mao Yijun, Qi Datong, Xu Qingyu Numerical study on high cycle fatigue failure of a centrifugal 
compressor impeller blades. Journal of Xi’an Jiao Tong University, Vol. 42, Issue 11, 2008, 
p. 1136-1139. 
[6] Fang X., Tang J., Jordan E., et al. Crack induce vibration localization in simplified bladed disk 
structures. Journal of Sound and Vibration, Vol. 291, Issue 1, 2006, p. 395-418. 
[7] Laxalde D., Thouverez F., Lombard J. P. Dynamical analysis of multistage cyclic structures. 
Mechanical Research Communications, Vol. 34, Issue 4, 2007, p. 379-384. 
[8] Laxalde D., Thouverez F., Lombard J. P. Dynamical multistage bladed disks systems. Journal of 
Engineering for Gas Turbines and Power Vol. 129, Issue 4, 2007, p. 1058-1064. 
[9] Yang Xingyu, Geng Zhongxing, Cai Xianghui Fracture analysis of the 2nd stage compressor blade 
in an aeroengine. Journal of Aerospace Power, Vol. 16, Issue 4, 2001, p. 327-330, (in Chinese). 
[10] Ejaz N., Salam I., Tauqir A. Fatigue failure of a centrifugal compressor. Engineering Failure 
Analysis, Vol. 14, Issue 7, 2007, p. 1313-1321. 


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