Impact of Impeller Stagger Angles on Pressure Fluctuation for a Double-Suction Centrifugal Pump
Fu et al. Chin. J. Mech. Eng.
Impact of Impeller Stagger Angles on Pressure Fluctuation for a Double-Suction Centrifugal Pump
Da‑Chun Fu 0 3
FuJ‑un Wang 0 2 3
PeiJ‑ian Zhou 1
Ruo‑Fu Xiao 0 2 3
Zhi‑Feng Yao 0 2 3
0 College of Water Resources and Civil Engineering, China Agricultural University , Beijing 100083 , China
1 College of Mechanical Engineering, Zhejiang University of Technology , Hangzhou 310014 , China
2 Beijing Engineering Research Center of Safety and Energy Saving Technology for Water Supply Network System, China Agri‐ cultural University , Beijing 100083 , China
3 College of Water Resources and Civil Engineering , China Agricultural Uni‐ versity, Beijing 100083 , China
Pressure fluctuation may cause high amplitude of vibration of double‑ suction centrifugal pumps, but the impact of impeller stagger angles is still not well understood. In this paper, pressure fluctuation experiments are carried out for five impeller configurations with different stagger angles by using the same test rig system. Results show that the stagger angles exert negligible effects on the characteristics of head and efficiency. The distributions of pressure fluctuations are relatively uniform along the suction chamber wall, and the maximum pressure fluctuation amplitude is reached near the suction inlet tongue region. The pressure fluctuation characteristics are affected largely by impeller rotation, whose dominant frequencies include impeller rotation frequency and its harmonic frequencies, and half blade passage frequency. The stagger angle exerts a small effect on the pressure fluctuations in the suction chamber while a great effect on the pressure fluctuation in volute casing, especially on the aspect of decreasing the amplitude on blade passage frequency. Among the tested cases, the distribution of pressure fluctuations in the volute becomes more uniform than the other impeller configurations and the level of pressure fluctuation may be reduced by up to 50% when the impeller stagger angle is close to 24° or 36°. The impeller structure pattern needs to be taken into consideration during the design period, and the halfway staggered impeller is strongly recommended.
Double‑ suction centrifugal pump; Impeller stagger angle; Pressure fluctuation; Frequency spectra analysis
Double-suction centrifugal pumps are widely used in
various fields, such as water diversion, farm irrigation,
urban water supply, and process industry. The flow rate
of a double-suction centrifugal pump is about twice
as much as a single-suction centrifugal pump with the
same diameter, and the axial force of the former pump is
theoretically balanced [
]. In long-distance water
diversion projects or high lift irrigations, double-suction
centrifugal pumps are playing increasingly important roles,
and the scales of which are becoming much larger. For
instance, the impeller diameter of a double-suction
centrifugal pump in Huinanzhuang pumping station in
China reaches 1.75 m, and its single installation power is
7500 kW [
The internal flow in a double-suction centrifugal pump
is extremely complex, especially under off-design
operating conditions [
]. The 3D asymmetric flow pattern in the
volute, the fluid dynamics of rotor–stator interaction, the
secondary flow, and the cavitation phenomenon induce
large pressure fluctuations [
]. Periodic pressure
fluctuation may force the impeller or volute to vibrate, and
resonance may occur when the frequency of pressure
fluctuation approaches the natural frequency of pump
components. The energy of pressure fluctuations
propagates in fluids at the speed of sound, which is harmful and
unacceptable to the pump and environment.
Furthermore, the lowest static pressure during fluctuation may
lead to cavitations [
]. Adverse operating conditions
may be detected by observing the pressure fluctuations
generated by a pump, which could provide evidence of
inadequate suction conditions [
Several studies have characterized the pressure
fluctuation of centrifugal pumps through experimental
investigations, theoretical analysis, and numerical simulations
]. Chu et al. [
] tested a single centrifugal
pump; built relationships among unsteady flow,
pressure fluctuation, and noise; and inspected the interaction
effect between the impeller and the volute. This study
showed that the impeller–volute tongue interaction and
the asymmetric outflow from the impeller are the two
main sources of high-level pressure fluctuations. When
the gap between the impeller and the volute tongue is less
than 20% of the impeller radius, the amplitude of pressure
fluctuation noticeably decreases as the gap increases. Stel
et al. [
] has recently presented a numerical
investigation of fluid flow in a centrifugal impeller with a vaned
diffuser. Significant levels of turbulence and
blade-oriented effects are revealed at different flow rates. Pei et al.
] found the optimization on the impeller of a
lowspecific-speed centrifugal pump can even reduce
pressure fluctuations. Gao et al. [
] analyzed the unsteady
flow inside a large centrifugal pump with stay vanes. The
main frequency of pressure fluctuation is the blade
passing frequency. The radial gap between the impeller outlet
and the volute tongue influences the overall performance
and the pressure fluctuations inside the pumps [
Hayashi et al.  analyzed the pressure fluctuations in a
piping system excited by a centrifugal turbomachinery by
considering the damping characteristics.
Alqutub et al. [
] investigated the effect of the V cut
of the impeller outlet on pressure fluctuation in
doublesuction centrifugal impellers and found that the V cut
decreases pressure fluctuation. Spence et al. [
numerically simulated a double-suction centrifugal pump with
impeller staggered at 0°, 15°, and 30°, and found that
the stagger impeller largely affects the characteristics of
pressure fluctuation. For such impeller configurations,
looking from the pump outlet section toward the twin
impellers, the blades of both impellers can be aligned
along the exit width or staggered. Yang et al. [
] and Li
et al. [
] implemented numerical simulations for
staggered impellers and illustrated that a suitable stagger
angle may reduce the amplitude of pressure fluctuations.
Yao et al. [
] reported that a double-suction
impeller with staggered bilateral blades can reduce pressure
fluctuations in comparison with the traditional impeller.
Staggered impellers have already been used in
Huinanzhuang pumping station, but the effect of stagger angle
on the pressure fluctuation remains unclear because of
the rare experimental investigations on this issue.
In the present study, pressure fluctuation experiments
are carried out for five impeller arrangements with the
same test rig system to establish the relationship between
impeller stagger angles and pressure fluctuations for a
double-suction centrifugal pump. High-accuracy
pressure transducers are mounted along the walls of the
semi-casing suction chamber and the volute casing.
Fluctuating pressure signals are captured and recorded under
different operation conditions. Time domains of the
pressure signals are analyzed using statistical methods and
Fast Fourier Transform (FFT). The influence of
impeller stagger angles on pressure fluctuations is obtained
2 Tested Pump and Experimental Setup
The tested pump (300ss-37) is manufactured by
Shandong Shuanglun Co., Ltd. (S.S.G.). The inlet and outlet
diameters of the pump are 300 and 250 mm, respectively.
The trailing edge of the original double-suction impeller
blade is parallel with the pump rotation shaft, and the
blades on both sides are arranged in a non-staggered
of the traditional double-suction impeller, the hubs of the
tested impellers extend to the impeller outlet. The main
design parameters of the test pump are given in Table 1.
The design flow rate is 1030 m3/h, the design head is
37 m, and the design efficiency is 85%. The design
rotational speed is 1480 r/min.
Both sides of the impeller are manufactured separately
to stager the double-suction impeller. Some specific key
slots are set on the pump shaft in the peripheral
direction. In this way, one side of the impeller can be
connected with keyways at a specific stagger angle with the
other side. According to the different impeller stagger
angles listed in Table 2, five impeller configurations are
shown in Figure 1. The stagger angles are 0°, 12°, 24°, 36°,
and 48°, which correspond to impellers 1, 2, 3, 4, and 5.
The absolute values of the stagger angles of impellers 2
and 5, as well as impellers 3 and 4, are exactly the same,
but the two sides of the blades are staggered in opposite
The experiment is carried out on the open test rig at
Shandong Shuanglun Co., Ltd. (S.S.G.). The investigated
pump is installed in the test rig containing all necessary
components to control the operating point of the pump.
The tested pump is driven by an electric AC-motor. The
shaft torque and rotating speed are measured by a torque
and speed sensor, respectively. Static pressure values at
the inlet and outlet of the pump are measured by a
pressure differential transfer. The flow rate is determined
by a magnetic flow meter. The total uncertainty of the
efficiency is around ± 0.5%. A scheme of the test rig is
shown in Figure 2.
For the pressure fluctuation measurement, Druck
PTX14000-15 piezoresistive high-frequency pressure
transducers are flush mounted in the wall of the
semispiral suction chamber and volute casing, the uncertainty
of which is ± 0.25%.
3 Arrangement of Pressure Measurement
The investigation mainly focuses on the effects of
pressure fluctuations on the semi-spiral suction chamber and
the volute casing caused by hydraulic excitations. In the
semi-spiral suction chamber, three measurement points
are proposed as shown in Figure 3(a). Location S3 is the
nearest to the inlet tongue of the suction chamber among
the three measurement locations. In the volute casing,
measurement points at five circumferential locations
in the volute casing wall are presented in Figure 3(b) to
obtain the specific frequencies of the pressure
fluctuations caused by the interaction between the impeller and
the volute tongue.
4 Test Procedure and Data Acquisition
The tested operating conditions are adjusted by the valve
located in the outlet pipe. Eleven operating conditions
are tested within the flow rate range of 0–1.2 Qn.
Pressure fluctuation transducers output 4–20 mA signals
over their operating range. The signals run across a
highaccuracy resistor to generate voltages that are recorded
synchronously with the sampling frequency of 2 kHz and
sampling time of 30 s by the acquisition unit. A low-pass
filter with a cut frequency of 500 Hz is set.
Figure 3 Measurement locations of pressure transducers
The peak-to-peak value in the time domain with 95%
confidence is adopted to evaluate the level of pressure
fluctuations. The FFT method is applied to obtain
frequency spectra, and the Hanning window is used to
realize the transform.
5 Results and Discussion
5.1 Performance Tests
During the energy performance tests, the pump is kept at
a constant rotational speed. The flow rate is changed by
adjusting the valve on the outlet pipe. The flow rate-head
curves for the five tested impeller configures are shown
in Figure 4. The flow rate-efficiency curves for five tested
impeller configures are shown in Figure 5. Results show
that the head only slightly decreases when the
doublesuction impeller is staggered. A comparison of the
performances at best efficiency points for the five impeller
configurations is shown in Table 3. The impeller stagger
angles may exert negligible effects on the pumping head
5.2 Pressure Fluctuations in the Semi‑spiral Suction
Frequency analysis of pressure fluctuations at different
flow rates in the semi-spiral suction chamber is carried
out. For each location, frequency analysis between 0 and
400 Hz is presented with results because of the absence of
obvious frequencies higher than 400 Hz. For comparison
with other scholars’ results [
5, 10, 20, 22
], the pressure
fluctuations are normalized to the pressure coefficient Cp
defined as Cp = (pi − p¯ i)/(0.5 ρu22). Where p¯ i is the
average value of the static pressure fluctuation during 10 s, pi
is the transient static pressure value, ρ is the fluid density,
and u2 is the impeller outlet circumferential velocity.
Figure 6 shows the time domains of the pressure
fluctuations on the best efficiency point at measurement points
0 200 400 600 800 1000
Flow rate Q / (m3● h-1)
Figure 4 Flow rate‑head curves
0 200 400 600 800
Flow rate Q / (m3● h-1)
Figure 5 Flow rate‑ efficiency curves
S1, S2, and S3 on the wall of the semi-suction chamber.
Ten periods of impeller rotation are compared for the
five impellers, and periodical pressure fluctuations are
observed. Among the three measurement points, the
highest level of pressure fluctuation appears on the
measurement point S3, which is located nearest to the inlet
tongue. The pressure fluctuation level is the lowest on
point S1. Such results may be explained by the different
distances between the suction chamber and the impeller
suction eye. Smaller distance may lead to larger pressure
fluctuation. Figure 7 shows the change in the
peak-topeak values of pressure fluctuations with the flow rate on
the three measurement points for the five impellers. The
trends of the peak-to-peak values changing with the flow
rate reach a basic agreement on measurement points S1,
S2, and S3. During the flow rate range of 0.6–1.0 Qn the
peak-to-peak values versus flow rate curves are almost
the same. The impeller stagger angle exerts negligible
effects on the flow field in the suction chamber.
The spectral domains of pressure fluctuations on
measurement points S1, S2, and S3 are shown in Figure 8,
which are all operating under nominal conditions. As
shown in Figure 8, the blade passage frequency (148 Hz),
half blade passage frequency (74 Hz), and four times
impeller rotation frequency (98 Hz) are clearly identified
in the frequency domains. For measurement point S1, the
largest amplitude of the pressure fluctuation appears at
frequency 98 Hz for impeller 5, which may be caused by
the mechanical source rather than the hydraulic reason.
The pressure fluctuation characteristics on point S2 are
similar to that on point S1. The blade passage frequency
component on point S2 is much more notable than the
one on point S1, which may reflect the effect of the
interaction between the impeller and the inlet tongue in the
suction chamber. For the pressure fluctuations on point
S3, the amplitudes at half blade passage frequency and
four times impeller rotation frequency are much larger
than that on points S1 and S2.
Figure 9 shows the spectra of the pressure fluctuations
at location S3 for impeller 1. The amplitudes of pressure
fluctuations on half blade passage frequency at 0.2 and
1.2 Qn are 3.9 and 1.6 times of that at the best efficiency
point, respectively. In addition, notable white noise
phenomenon is present for the pressure signals under 0.2 and
0.6 Qn operating conditions. As mentioned by Liu [
white noise phenomenon may cause the complex
turbulence flow inside the suction region of the test pump.
The pressure fluctuations on half blade passage
frequency in Figure 9 show that the amplitude of the
pressure fluctuation on such frequency at l.2 Qn is two
times as large as that at 1.0 Qn. According to the
pressure fluctuations reflected by the three measurement
points, the characteristics of pressure fluctuations in the
suction chamber present a homogeneous distribution.
The maximum amplitude of the pressure fluctuations is
reached at location S3, which is nearest to the suction
chamber inlet tongue. The pressure fluctuations in the
suction chamber are considerably affected by the
rotation effect, of which the frequencies are manifested as
the harmonic of impeller rotation frequency and half
blade passage frequency.
5.3 Pressure Fluctuations in the Volute Casing
In the volute casing, a pronounced pressure fluctuation
pattern can be caused by the interaction between the
impeller blades and the volute tongue [
]. Figure 10
illustrates the time domains and their corresponding
spectral domains at the best efficiency point on
measurement point P1. Compared with the frequencies of
pressure fluctuations in the suction chamber, the frequencies
of pressure fluctuations in the volute are much higher and
complicated. The periodicity of the pressure fluctuation
in the time domain is not obvious because of the
superposition of several frequency components. According to
the shown spectra, the main frequencies in the volute
are the impeller rotation frequency and its harmonic (25
150 200 250
a Measurement point S1
150 200 250
b Measurement point S2
and 100 Hz), the half blade passage frequency (74 Hz),
the blade passage frequency and its harmonics (148 and
296 Hz), and the broadband frequency [
Comparing with that at location P1, the periodicity of
the pressure fluctuations at location P2 is much more
obvious. The dominant frequency of pressure
fluctuation, which is the blade passage frequency, is much more
remarkable than that in impellers 1, 2, and 5 (Figure 11).
The amplitudes of the pressure fluctuations at the blade
passage frequency at location P2 for impellers 3 and 4 are
very small [
], and the broadband frequency is observed
near the half blade passage frequency.
Figure 12 shows the time and frequency domains of
measurement point P3 at the best efficiency points for
the five impellers. Measurement point P3 is far from the
volute tongue, and the level of pressure fluctuation at the
blade passage frequency is lower. The harmonic
frequencies of the blade passage frequency dominate the
Figure 13 presents the time and frequency domains of
measurement point P4 at the best efficiency points for
the five impellers. The broadband components greatly
affect the pressure fluctuation behaviors at this location.
The time and frequency domains of measurement point
P5 at the best efficiency points for the five impellers are
given in Figure 14. The measurement location is set in the
outer volute section, and the characteristics of the
pressure fluctuations at this location are basically the same as
that at location P4.
Figure 15 shows the peak-to-peak values of the pressure
fluctuations as a function of flow rate for the five
impellers. In consideration of the above results, the stagger
angle greatly affects the pressure fluctuations at location
P2. The pressure fluctuation of the staggered impeller is
decreased. In addition, the peak-to-peak values of
impellers 3 and 4 reduce to 50% compared with that of
impeller 1. Impellers 3 and 4 have the lowest level of pressure
fluctuations, and their impeller stagger angle is 24° or
36°, which is close to 360/(2·Z). The stagger angle mainly
affects the component of the blade passage frequency but
exerts negligible effects on the other components.
Figure 16 present the peak-to-peak values of
pressure fluctuations on the volute at different flow rates for
impellers 1 and 4. For impeller 1, the peak-to-peak
values at locations P1 and P2, which are close to the volute
tongue, are relatively large. The peak-to-peak value is
small at locations P4 and P5 set in the diffuse section of
the volute, and the smallest one is found at location P3,
which is far from the volute tongue. For impeller 4, the
change trends of the peak-to-peak values with flow rate
0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36 0.40
a Time domains
are even, and the discrepancies of the different locations’
trends become small. This result is also supported by a
previous computational fluid dynamics study [
Figure 17 shows the spectra of pressure fluctuations at
location P2 for impellers 1 and 4 under the five
operating conditions. As observed in the spectra of impeller 1,
0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36 0.40
a Time domains
0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36 0.40 0 100 200 300 400 500 600 700 800 900 1000
Time t/s Frequency f/Hz
a Time domains b Frequency domains
Figure 14 Time and frequency domains of pressure fluctuations on measurement point P5 at best efficiency points
the dominant frequency is always the blade passage
frequency, and the broadband component displays
remarkably only at 1.2 Qn, thereby increasing the peak-to-peak
value of the pressure fluctuations. For impeller 4, the
blade passage frequency only exists at flow rates below
0.6 Qn. The corresponding amplitude at 0.2 Qn is one
Fu et al. Chin. J. Mech. Eng. (2018) 31:10
tenth of that in impeller 1. The broadband of these two
impellers demonstrates the same behaviors. The center
frequency of the broadband component decreases with
increasing flow rate. For impeller 4, some low frequencies
of the pressure fluctuations below 0.6 Qn may be induced
by the shedding of stall cells as investigated by Zhou [
The above results suggest that the stagger angle
definitely affects the pressure fluctuation characteristics in
the volute casing; in particular, it decreases the amplitude
on the blade passage frequency. When the impeller
stagger angle is 24° or 36°, the distribution of pressure
fluctuations in the volute casing becomes more uniform than
the other impeller configurations, and the level of
pressure fluctuation can be reduced by up to 50%. Staggered
impellers may redistribute the flow pattern at the region
of the impeller outlet and affect the jet-wake flow field.
In this way, the staggered impeller changes the strength
of the interaction between the impeller and the volute
1. Five impeller configurations with the same test rig
system are investigated. The pressure fluctuations are
captured along the walls of the semi-casing suction
chamber and the volute casing. The time domain and
frequency spectra are carefully identified using
statistical methods and Fast Fourier Transform.
2. The stagger angles exert negligible effects on the
characteristics of head and efficiency. Compared with
the traditional parallel impeller, the staggered
impeller slightly decreases the pump head.
3. The distributions of pressure fluctuations are
relatively uniform along the suction chamber wall, and
the maximum pressure fluctuation amplitude is
reached near the inlet tongue region.
4. The dominant pressure fluctuation frequencies are
composed of impeller rotation frequency and its
harmonic frequencies, and half blade passage frequency.
5. The stagger angle exerts minimal effects on the
pressure fluctuations in the suction chamber but greatly
affects the pressure fluctuation characteristics in the
volute casing. In particular, this parameter decreases
the amplitude on the blade passage frequency. When
the impeller configuration is nearly halfway
staggered, the distribution of pressure fluctuations in the
volute casing becomes more uniform than the other
impeller configurations, and the level of pressure
fluctuation may be reduced by up to 50%.
DCF carried out the experiments, participated in the data post processing and
drafted the manuscript. FJW provided guidances on the experiment design
and the data analysis methods. PJZ and RFX participated in the experiments.
ZFY sponsored the research, participated in the entire process of the research.
All authors read and approved the final manuscript.
Da‑ Chun Fu, born in 1970, is currently a Ph.D. candidate at College of Water
Resources and Civil Engineering, China Agricultural University, China. He received
his master degree from China University of Petroleum (East China), China, in
2010. His research interests include operating stability and pressure fluctua‑
tion characteristics of centrifugal pumps. Tel: +86‑137‑01207037; E‑mail:
Fu‑ Jun Wang, born in 1964, is currently a professor at China Agricultural
University, China. He received his Ph.D. degree from Tsinghua University, China,
in 2000. His research interests mainly include computational fluid dynamics
of hydraulic machines, transient flow phenomena in pumping system, design
theory of turbomachines and fluid–structure interaction. E‑mail: wangfj@cau.
Pei‑ Jian Zhou, born in 1986, is currently a lecturer at Zhejiang University of
Technology, China. He received his Ph.D. degree from China Agricultural
University, China, in 2015. His research interests mainly include stall characteristics in
centrifugal pumps. E‑mail: .
Ruo‑Fu Xiao, born in 1976, is currently a professor at China Agricultural
University, China. He received his Ph.D. degree from Huazhong University of
Science and Technology, China, in 2004. His research interests mainly include
flow theory of hydraulic machines, optimization design of turbomachines and
fluids‑structure interaction. E‑mail: .
Zhi‑Feng Yao, born in 1984, is currently an associate professor at China
Agricultural University, China. He received his Ph.D. degree from China
Agricultural University, China, in 2013. His research interests mainly include hydrody‑
namic damping of hydraulic machines, pressure fluctuation characteristics
of centrifugal pump, and design theory of pumping stations. Tel: +86‑158‑
11134516; E‑mail: .
Supported by National Natural Science Foundation of China (Grant Nos.
51621061, 51139007, 51409247), and National Science and Technology Sup‑
port Project of China (Grant No. 2015BAD20B01).
The authors declare that they have no competing interests.
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Springer Nature remains neutral with regard to jurisdictional claims in pub‑
lished maps and institutional affiliations.
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