Vacuum Journal CFturbo Influence Blade Outlet Angle Centrifugal Pump Performance
Vacuum Journal CFturbo Influence Blade Outlet Angle Centrifugal Pump Performance
Vacuum Journal CFturbo Influence Blade Outlet Angle Centrifugal Pump Performance
Vacuum
journal homepage: www.elsevier.com/locate/vacuum
A R T I C LE I N FO A B S T R A C T
Keywords: The blade outlet angle β2 is one of the key design parameters of the centrifugal pump, which has an important
Centrifugal pump influence on the internal flow field and performance of centrifugal pump. In this paper, five impeller models with
Blade outlet angle different blade outlet angles (23°, 25°, 27°, 29° and 31°) were built by Solidworks and CFturbo under the premise
High specific speed of other impeller parameters unchanged, and numerical simulation of high specific speed (ns = 192) pump was
Hydraulic performance
carried out in the commercial code ANSYS-CFX. Then the experiment was performed to test the hydraulic
performance of centrifugal pump. The results show that the change trend of numerical simulation and experi-
ment is similar, and when the flow rate increases gradually, the hydraulic loss of impeller becomes larger with
the increase of blade outlet angle, and the blade outlet angle has obvious influence on the efficiency of cen-
trifugal pump at high flow rate. Besides that, it has small influence on the head, which changes relatively larger
at low flow rate than that at high flow rate. And all the research results could provide appropriate reference for
designers to select reasonable outlet angle.
1. Introduction the pump at the design operating point. Bacharoudis et al. [9] designed
a laboratory pump that could suit radial impellers with the same dia-
High specific speed centrifugal pump is the type of centrifugal pump meter, and the experimental results showed that the performance curve
with specific speed of 150–300, which has larger flow rate and lower become smoother and flatter with the increase of outlet blade angle.
head. And it is widely used in the fields such as agricultural en- Combining numerical simulation with experiment, Shi et al. [10]
gineering, aerospace engineering, chemical industry etc. With the rapid proved that it was feasible to optimize the performance of deep well
development of computer technology and computational fluid dy- centrifugal pump by changing the width of impeller outlet. Yang et al.
namics (CFD), numerical simulation has become an effective method to [11] analyzed the influence of variation of blade thickness and profile
analyze the inner flow and performance of centrifugal pump. There are on centrifugal pump performance. Zhang et al. [12] promoted a new
many researches on centrifugal pump performance using CFD method numerical hydraulic design method for the low specific centrifugal
in Refs. [1–5], and the researches have proved the feasibility of nu- pump impeller, which realized fast design and optimization. Cui et al.
merical simulation using CFD method. [13] analyzed the influence of blade outlet angle on inner flow field and
As the performance of centrifugal pump depends on many para- performance of low-specific-speed centrifugal pump. Zhou et al. [14]
meters such as blade number, blade wrap angle, blade thickness, blade have studied the effect of different rear shroud radius on hydraulic
outlet angle etc., many researchers have studied the influence of dif- performance.
ferent parameters. Liu et al. [6] found that the head of centrifugal pump In addition, Li et al. [15] studied the unsteady flows caused by the
grows with the increase of blade number, and there is an optimum interaction between impeller and volute of a high-speed micro cen-
value for the efficiency and cavitation characteristics. Tan et al. [7] trifugal pump. Yang et al. [16] studied the effects of blade outlet angle
studied the influence of blade wrap angle on centrifugal pump perfor- and medium temperature on the crystallization rate. Nishi et al. [17]
mance, and concluded that the pump with large wrap angle has wide analyzed the radial thrust of a single blade centrifugal impeller with
area for high efficiency and stable operation. Pan et al. [8] analyzed the two different blade outlet angles, and concluded that the larger blade
effects of three variation blade angles on centrifugal pump perfor- outlet angle had better performance. Shigemitsu et al. [18] studied the
mance, and found that slip theory can accurately calculate the head of effect of blade outlet angle on the performance of turbo pump, and
∗
Corresponding author.
E-mail addresses: dhchang@sdust.edu.cn (H. Ding), 649339038@qq.com (Z. Li), 528173250@qq.com (X. Gong), 1101947185@qq.com (M. Li).
https://doi.org/10.1016/j.vacuum.2018.10.049
Received 13 August 2018; Received in revised form 19 October 2018; Accepted 19 October 2018
Available online 22 October 2018
0042-207X/ © 2018 Elsevier Ltd. All rights reserved.
H. Ding et al. Vacuum 159 (2019) 239–246
proposed a high performance design with simple structure. Zhang et al. Table 1
[19] concluded that the radial force of the impeller increases gradually Main parameters of centrifugal pump.
with increasing β2. Dong et al. [20] used boundary element method to 95 143 24 23
identify the effect of blade outlet angle, and concluded that a suitable
blade outlet angle of 30° could ensure a better comprehensive perfor- Suction Impeller Outlet Inlet
diameter diameter width blade angle
mance of the PAT. Lang et al. [21] adopted acoustic-vibro-coupling
Dj/mm D2/mm b2/mm β1(°)
method to calculate the fluid field of centrifugal pump models with Outlet Blade Blade Blade
different blade outlet angle. Su et al. [22] studied the numerical and blade angle wrap angle number thickness
experimental method on multi-stage pump as a turbine system. β2/(°) Φ/(°) Z δ/mm
In summary, CFD numerical simulation has been proved to be a
27 120 5 3
useful method for analyzing the performance of centrifugal pump, and
there are some researches about the pump performance with different
blade outlet angles, and a lot of achievements have been obtained. But the shape of impeller blade is designed to be a twisted blade, as the
in the exiting studies, the model is mainly concentrated on the low centrifugal pump has a high specific speed.
specific speed pump, and there is little study on high specific speed Fig. 2(a) shows the blade outlet angle in the 2-D sketch of impeller,
centrifugal pump. In this paper, the model of high specific speed cen- which is an included angle between tangent and circumferential di-
trifugal pump is built in Solidworks and CFturbo, and the numerical rection at the edge of blade outlet. Fig. 2(b) shows the 3-D model of
simulation is done by using commercial code ANSYS-CFX. The internal impellers established by Solidworks and CFturbo, which are used to
flow and performance of pump with different blade outlet angles are perform the numerical simulation in ANSYS-CFX, and there is almost no
studied, and experiments are carried out to verify the performance of difference in appearance of the 3-D models with different blade outlet
centrifugal pump. The research results could provide appropriate re- angle.
ference for designers to select reasonable blade outlet angle.
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H. Ding et al. Vacuum 159 (2019) 239–246
shown in Fig. 4. It can be seen that the head of scheme Ⅰ is biggest Table 2
among the three schemes, and the head of scheme Ⅱ almost equals that Mesh schemes for grid independence check.
of scheme Ⅲ, which means that the grid numbers of model increase to a Mesh scheme Inlet Impeller Volute
certain value, the predicted head eventually will tend to be a constant
value. So the scheme II is finally chosen according to the calculation Ⅰ 308714 210238 493180
time and grid independence. Ⅱ 421208 282283 664958
Ⅲ 600898 376650 944017
∂U
∂t
+ ∇⋅F1 + ∇⋅FV = ϕ
(1)
• Fluid in the centrifugal pump is water with a density of 1000 kg/m , 3
where μt is the molecular viscosity coefficient, ρ is the density, k is the 2.5. Model verification
turbulence energy, Gk is the turbulent kinetic energy caused by velocity
gradient, u is velocity of liquid, and ε is the turbulence dissipation In order to verify the feasibility of the model pump for simulation,
rating. hydraulic performance test is performed on the IS100-80-125 pump,
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H. Ding et al. Vacuum 159 (2019) 239–246
3. Results and analysis Supposing that the working flow rate of the centrifugal pump is
from 80 m3/h to 120 m3/h, and the design flow rate equals 100 m3/h.
3.1. Prediction algorithm According to Eqs. (5)–(9), the external characteristic curves of the
centrifugal pump with different blade outlet angles can be obtained, as
Head of centrifugal pump (H) is calculated as follows: shown in Fig. 7.
pout − pin Fig. 7 (a) shows that the head of the centrifugal pump increases with
H= the increase of blade outlet angle at low flow rate of 80 m3/h. As the
ρg (5)
flow rate increases, the influence of blade outlet angle on the head
where pout is the total pressure of volute outlet, pin is the total pressure becomes weak. Fig. 7 (b) shows that the general trend of efficiency
of impeller inlet, ρ is the density of the fluid, and g is the gravity ac- firstly increases and then decreases with the increase of flow rate, and
celeration. the maximum efficiency corresponds to the design flow rate. At low
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H. Ding et al. Vacuum 159 (2019) 239–246
flow rate, the small blade outlet angle has a lower efficiency than that increase of the blade outlet angle at low flow rate condition.
of big angle, and the trend becomes opposite at high flow rate. The
maximum efficiency difference between different blade outlet angles is 3.4. Relative velocity distribution
about 1.5% at design flow rate, and when the flow rate increases to
120 m3/h, the efficiency difference reaches to about 5.7%. And it can be Fig. 9 shows the relative velocity distribution of the impeller and
concluded that the blade outlet angle has a significant effect on the volute. It can be seen that the relative velocity of the fluid in the im-
efficiency of centrifugal pump. peller increases gradually, and the velocity has minimum value and
smaller gradient in uniform flow at the impeller inlet. At the impeller
3.3. Pressure distributions outlet, with the rise of blade outlet angle, the flow velocity increases
and the flow becomes unstable, and the velocity at the pressure surface
The pressure distributions of impeller are shown in Fig. 8. It can be is bigger than that on the back. When the fluid flows into the volute, the
seen that the pressure gradually increases from the impeller inlet to velocity would decrease gradually because of the diffusion structure of
outlet, the pressure at the inlet has the smallest value and a large gra- volute, and the velocity field of the impeller near the tongue shows
dient. The pressure is bigger on the pressure surface than that on the certain fluctuations. In addition, the velocity field distribution of the
suction surface at the same position, so the back surface of inlet is the impeller with different outlet angles is consistent, but the velocity field
position where cavitation is prone to occurrence. Due to the obstruction distribution of tongue is quite different.
effect, the pressure of the tongue part has certain fluctuations. By To observe the relative velocity distributions of volute tongue more
comparing the pressure distributions in Fig. 8, it can be concluded that clearly, enlarging the volute tongue part of Figs. 9, and Fig.10 can be
the pressure of impeller inlet first decreases and then increases, and the obtained. In Fig. 10, the velocity gradient at tongue increases with the
change trend of pressure distribution is consistent under different outlet increase of outlet angle, and the channel between the adjacent blades
angles. Note that the pressure near the tongue will increase with the becomes shorter, which leads to more serious diffusion of velocity in
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the tongue, and it will cause certain hydraulic loss. is composed of three parts: centrifugal pump, water tank and circula-
tion pipeline. The flow rate is regulated by the discharge valve, and the
4. Experiment flow rate is measured by the LWGY-MIK turbine flowmeter, whose
measuring accuracy reaches to ± 1%R. The centrifugal pump is driven
Fig. 11(a) shows the five rapid prototyping plastic impellers, which by Y160M1-2 motor, whose parameters are: rated voltage 380 V, rated
are installed to the experimental pump for performance testing. And the power 11kw, frequency 50 Hz. And the pressure gauge and vacuum
external performance of centrifugal pump with different blade outlet meter are installed at the inlet and outlet of centrifugal pump, which
angles is tested in the open test rig, as shown in Fig. 11(b). The test rig are used to measure the pressure.
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The comparisons between experiment and calculation curves of Therefore, it is necessary to choose the appropriate blade outlet angle
centrifugal pump with different outlet angle are shown in Fig. 12. It can when designing the centrifugal pump impeller.
be seen from Fig. 12 that the head and efficiency of the centrifugal In Fig. 12, it can be seen that the change trend of numerical simu-
pump decreases with the rise of blade outlet angle at the same rate. At lation and experiment is similar, and the results of experiment are less
design point, when the blade outlet angle equals 23°, the head and ef- than that of simulation, which are caused by the greater hydraulic loss
ficiency of experiment are 21.20 m, 76.12%, respectively. When the in experiment. And there is a little difference at low flow rate for the
blade outlet angle equals 31°, the head and efficiency are 20.55 m, head and efficiency. The max error of head reaches about to 1.8 m
73.94%, respectively. Therefore, it can be concluded from the experi- between the simulation and experiment at low flow rate with angle of
mental data that when the blade outlet angle increases from 23° to 31°, 31°. In addition, the max error of efficiency reaches about 0.03 between
the head decreases by 0.65 m, and the efficiency decreases by 2.18%. simulation and experiment at design flow rate with angle of 31°, and
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