ijmet 06 08_010

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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 CPD

TM 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.

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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 CPD

TM

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


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


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

Pre

ssu

re

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

Pre

ssu

re

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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