Centrifugal Pump Blade Analysis

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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 6, Issue 8, Aug 2015, pp. 105-117, Article ID: IJMET_06_08_010
Available online at
http://www.iaeme.com/IJMET/issues.asp?JTypeIJMET&VType=6&IType=8
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
________________________________________________________________________
NUMERICAL ANALYSIS OF THE EFFECT
OF THE NUMBERS OF BLADES ON THE
CENTRIFUGAL PUMP PERFORMANCE AT
CONSTANT PARAMETERS
Hayder Kareem Sakran
Chemical Engineering, Engineering College/ AL Muthanna University, Samawa, Iraq
ABSTRACT
In the present paper, the performance of a centrifugal pump with the same
parameters which are the head, rotating speed, volume flow rate and the
outlet diameter; however, with different number of blades has been
investigated numerically by Computational Fluid Dynamics (CFD) using
Shear Stress Transport (SST) as a turbulence model. The simulation has been
done using ANSYS®
, Vista CPDTM
Release 15.0, to study the effect of the
variation of the blade number on the centrifugal pump performance.
The numerical study has been carried out by obtaining the pressure for
three different conditions of a centrifugal pump in which each one has the
same parameters, but with different numbers of blades that start from five to
sixteen. The simulation showed strong results. The pressure increases
obviously with a specific number of blades then decreases. Thus, each
centrifugal pump with exact parameters has a perfect performance at specific
blade number.
Key words: ANSYS®
, Vista CPDTM
Release 15.0, Centrifugal pump, CFD,
Number of blades, Numerical Simulation.
Cite this Article: Hayder Kareem Sakran, Numerical Analysis of The Effect
of The Numbers of Blades on The Centrifugal Pump Performance at Constant
Parameters. International Journal of Mechanical Engineering and
Technology, 6(8), 2015, pp. 105-117.
http://www.iaeme.com/currentissue.asp?JType=IJMET&VType=6&IType=8
_______________________________________________________________
1. INTRODUCTION
Centrifugal pumps have a widely application at several locations such as industrials,
agricultures and domestics. The main benefit of the centrifugal pump is to transfer the
mechanical energy to a fluid by pressure rising.

There are a few investigations studied the effect of the blade number on the
performance of the centrifugal pump in which too few numbers of blades in
centrifugal pump lead to the circulatory flow loss phenomena because of the
magnitude of the tangential velocity vector (V2, t) at the outer circumstance of the
impeller will not be equalized, since it will be a bigger at the trailing edge than at the
gap between the impeller blades as shown in Fig. [1]. While using too much number
of blades the passage loss phenomena will happen due to the blockage and the skin
friction drag; so that the flow speed at the circumstance of the impeller will not be
identical and that will affect the actual net head and the pump’s efficiency as shown in
Fig. [1]. So the suit number of blades for the centrifugal pump can give a good
performance.
Figure 1 The impeller of the centrifugal pump. [1]
Wee (2011, 5) found that the flow field with the impeller passage is a very
complicated and it depends on the number of blades. [2]. Impeller’s flow direction
can get large control with a large number of blades; with increasing the blockage
because that will create a large ratio between the solid and fluid during fluid flow by
the impeller [3]. The design of the angle of the impeller blade and the tip width can
impact with the increment. Both the relative flow angles at the trailing edge β2 and the
tip width are affected by the increasing of the impeller blade number as shown in
figure (2). [3].
Figure 2 The relation between the tip width, flow angle and the number of blades. [3]

Numerical Analysis of The Effect of The Numbers of Blades on The Centrifugal Pump
Performance at Constant Parameters
Figure (2) shows the increasing of the flow angle β2 with the increasing of the
number of blades; however, the tip width decreases at a specific number of blades (4
to 10). [3].
Another parameter that is affected by the number of blades is the Busemann slip
factor, SfB, when the solidity is more than 1.1 (s>1.1). Busemann slip factor, SfB, can
tend to unity with large number of blades which also can tend to increase the
frictional losses as shown in figure (3). [4]
Figure 3 The relation between the Busemann slip factor, SfB, and the blade angle, βb, for
different numbers of blades, ZR. [4]
The number of blades also can control the centrifugal pump design depending on the
fluid kind. If the centrifugal pump is used to deliver a liquid, the impeller will have a
smaller number of blades than the impeller in the centrifugal pump that is used to
deliver a gas, because of the centrifugal pump that is used to deliver a liquid should
have thicker blades than the other [4]. Stepanoff (1948) found that “the number of
blades should be one third of the discharge blade angle, βb (in degrees)”. [5].
This paper focuses on analyzing three different cases of water flow through a
centrifugal pump with constant parameter which is the head, rotating speed, volume
flow rate and the outlet diameter. Furthermore, it deals with the effect of the variation
of the number of blades on the performance of the centrifugal pump.
2. SIMULATION AND NUMERICAL ANALYSIS
The Turbomachinery problem has been simulated and analyzed numerically by
Computation Fluid Dynamics (CFD) using Shear Stress Transport (SST) turbulence
model to solve the governing equation. A CFD is a common tool used to study and to
gain a good understanding about the flow domain inside the centrifugal pump
numerically.

Figure 4 3D geometry of the centrifugal pump
The three-dimensional geometry has been created using ANSYS®
, Vista CPDTM
Release 15.0 to simulate a steady state conditions and incompressible fluid flow
problem. The problem specification and the boundary conditions are explained briefly
in the tables1, 2, and 3 for the three cases.
Table 1 Problem Specification and Boundary Conditions for case 1
Case 1
Parameters Problem Specification and Boundary Conditions
Rotational Speed 3500 r.p.m
Volume Flow Rate 54 m3
/hr
Head Rise 25 m
Number of Blades From 5 to 16
Inlet Flow Angle 90 deg
NPSHr 3.59 m
Head Coefficient 0.442
Flow Coefficient 0.040
Machine Type Centrifugal Pump
Suction specific speed, Nss 3.15
Turbulence Model Shear Stress Transport (SST)
Fluid Water at Standard Conditions
Analysis Type Steady State
Inflow/Outflow Boundary Template Mass Flow Inlet/P-Static Outlet

Unstructured fine mesh has been employed for the flow domain and the details of
the mesh are shown in tables 4, 5 and 6 for the three cases.
Case 2
Volume Flow Rate 64.8 m3
/hr
Head Rise 28 m
NPSHr 4.53 m
Case 3
Volume Flow Rate 72 m3
/hr
Head Rise 30 m
NPSHr 5.20 m

Figure 5 Mesh generation.
Table 4 Mesh Information for Case 1
Mesh Information for Case 1
Number of
Blades
Number of
Nodes
Number of
Elements
Tetrahedra Wedges Hexahdra
5 367398 469893 112413 76200 281280
6 363598 466441 113426 76535 276480
7 354798 454506 111006 75120 268380
8 356224 453857 110052 73535 270270
9 361226 457934 110334 74060 273540
10 369962 466693 110978 74195 281520
11 361596 457613 110328 73775 273510
12 364925 460081 109666 73695 276720
13 360636 457641 111431 74680 271530
14 366627 461938 109833 74725 277380
15 363976 460588 110483 76175 273930
16 350109 448723 112398 76195 260130
Mesh Information for Case 2
Number of
Blades
Number of
Nodes
Number of
Elements
5 365550 471726 115871 77395 278460
6 367587 472590 116325 76755 279510
7 362937 466370 114765 76385 275220
8 366906 467909 114654 74885 278370
9 369760 468773 113378 74295 281100
10 374023 473264 113939 74805 284520
11 365776 465047 114162 74705 276180
12 372905 473366 115551 75455 282360
13 365156 465599 115334 75615 274650
14 365644 465959 114784 76525 274650
15 364781 467194 116879 77165 273150
16 361670 462714 115889 76645 270180

Mesh Information for Case3
Number of
Blades
Number of
Nodes
Number of
Elements
5 366511 473422 117242 76460 279720
6 360896 467498 117953 76395 273150
7 365220 470358 116888 76510 276960
8 355241 460021 116946 75775 267300
9 374953 476653 116478 75265 284910
10 366545 467410 115645 74775 276990
11 368864 469997 116027 75150 278820
12 363307 465224 116634 75740 272850
13 365181 466948 116568 75940 274440
14 362604 465607 117067 77550 270990
15 355524 457851 116691 76470 264690
16 362179 464683 117513 76690 270480
3. RESULTS AND DISCUSSION
After complementation of the mesh generation, the solution has been obtained when
the convergence is done, which is happening after 1000 times of iterations. The
solution has three different groups of results depend on the conditions of the problem
which are explained below:
3.1. Case One
This case done when the centrifugal pump is investigated with 3500 r.p.m, 25 m of
head, 54 m3
/hr, and with different number of blades which are from 5 to 16 as shown
in table1. The results showed different magnitudes of pressure as shown in table7.
Table 7 Pressure at case1.
Number of Blades Pressure in [Pa]
5 3.579E+04
6 3.735E+04
7 3.769E+04
8 3.540E+04
9 3.992E+04
10 4.533E+04
11 4.089E+04
12 3.888E+04
13 4.066E+04
14 3.830E+04
15 4.074E+04
16 3.917E+04

Figure 6 Pressure variation in case 1.
Figure 7 Pressure magnitude at case 1 to the pump with ten blade number and eight blade
number
The figures show good results in case 1, the pressure gets highest magnitude when
the number of blades is ten. However, the magnitude of pressure has a smallest
amount when the number of blades is eight.
3.2. Case Two
head, 64.8 m3
/hr, and with different number of blades which are from 5 to 16 as
shown in table1. The results showed different magnitudes of pressure as shown in
table 8.
3.0E+04
3.2E+04
3.4E+04
3.6E+04
3.8E+04
4.0E+04
4.2E+04
4.4E+04
4.6E+04
4.8E+04
5.0E+04
4 5 6 7 8 9 10 11 12 13 14 15 16 17
Pressure
Number of Blades
pump with 25 head and 3500 rpm

Table 8 Pressure in case 2
5 4.385E+04
6 4.187E+04
7 5.264E+04
8 5.228E+04
9 5.370E+04
10 5.274E+04
11 4.659E+04
12 4.603E+04
13 4.543E+04
14 4.702E+04
15 4.650E+04
16 4.143E+04
Figure 8 Pressure variation in case 2
the number of blades is nine. However, the magnitude of pressure has a smallest
amount when the number of blades is sixteen.
2.0E+04
2.5E+04
3.0E+04
3.5E+04
4.0E+04
4.5E+04
5.0E+04
5.5E+04
6.0E+04
6.5E+04
7.0E+04
4 5 6 7 8 9 10 11 12 13 14 15 16 17
Pressure
Number of Blades

Figure 9 Pressure magnitude at case 2 to the pump with nine blade number and sixteen blade
number
3.3. Case Three
head, 64.8 m3
/hr, and with different number of blades which are from 5 to 16 as
shown in table1. The results showed different magnitudes of pressure as shown in
table 9.
Table 10 Pressure in case 3
5 4.766E+04
6 4.537E+04
7 5.880E+04
8 6.296E+04
9 6.087E+04
10 5.342E+04
11 5.639E+04
12 4.932E+04
13 4.988E+04
14 5.000E+04
15 5.402E+04
16 5.029E+04

Figure 10 Pressure variation in case 3
Figure 11 Pressure magnitude at case 3 to the pump with eight blade number and six blade
number
the number of blades is eight. However, the magnitude of pressure has a smallest
amount when the number of blades is six.
4. CONCLUSION
A centrifugal pump with different number of blades has been investigated numerically
using computational fluid dynamics. A commercial code, ANSYS©
, Vista CPD©
R15.0 was used to simulate the flow domain. Three different cases with constant
parameter have been carried out numerically to study the effect of the variation of
blades number on the pump performance. A simulation shows a good result which can
be repeated with different pump parameters, then chose the best number of blades for
each case and that can gain a good benefit for perfect pump design which can help the
pump industry to make a pump chart that can have the perfect pump performance with
the suitable number of blades.
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