The design of a single rotor axial flow fan for a cooling tower application

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THE DESIGN OF A SINGLE ROTOR AXIAL FLOW FAN FOR A COOLING TOWER APPLICATION

Phillippe Roger Paul Bruneau

Thesis presented in partial fulfillment of

the requirements for the degree of Master of

Engineering (Mechanical) at the University of

Stellenbosch

Thesis Supervisor

Prof. T.W. von Backstrom

Department of Mechanical Engineering

University of stellenbosch

December 1994

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Declaration

I, Phillippe Roger Paul Bruneau, the undersigned, hereby declare that this thesis is my own original work. It is being submitted for the Degree of Master of Engineering (Mechanical) at the University of Stellenbosch. It has not previously been sub-mitted, in its entirety or in part, for any degree or examination in any other University.

AJ~~

.._

... .If) :

7. ••••••••• Signature of candidate

This 10

t:i-

day of

l1-~ft

1994

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Abstract

A design methodology for low pressure rise, rotor only, ducted

axial flow fans is formulated, implemented and validated using

the operating point specifications of a 1/6th scale model fan

as a reference. Two experimental fans are designed by means of

the design procedure and tested in accordance with British

Standards 848, Type A.

The design procedure makes use of the simple radial equilibrium

equations,

embodied

in a

suite of computer programs.

The

experimental fans have the same hUb-tip ratio and vortex

dis-tribution, but differ in the profile section used.

The first

design utilises the well known Clark-Y aerofoil profile whilst

the second takes advantage of the high lift characteristics of

the more modern NASA LS series.

The characteristics of the two designs are measured over the

entire operating envelope and compared to the reference fan

from which the utility and accuracy of the design procedure is

assessed.

The performance of the experimental fans compares

well with both the reference fan as well as the design intent.

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Opsomminq

'n Ontwerpmetode vir lae drukstyging, enkel rotor aksiaal waaiers is geformuleer, toegepas en bevestig deur gebruik te maak van die ontwerppunt spesifikasies van 'n 1/6 skaal verwysingswaaier. Twee eksperimentele waaiers is ontwerp deur middel van die ontwerpmetode en getoets volgens die BS 848, Type A kode. Die ontwerpmetode maak gebruik van die eenvoudig radiale ewe-wigsvergelykings en 'n stel rekenaarprogramme. Die twee eksperimentele waaiers het dieselfde naaf-huls verhouding en werwel verdeling, maar verskil daarin dat verskillende vleuelprofiele gebruik is vir elkeen van die twee waaiers. Die eerste ontwerp maak gebruik van die bekende Clark-Y profiel terwyl die tweede die moderne NASA LS profiel gebruik.

Die karakteristieke van die twee eksperimentele waaiers is gemeet oor die hele werkbereik en vergelyk met die verwysings waaier waardeur die geldigheid en akkuraatheid van die ont-werpmetode bepaal is. Die werkverigting van die eksperimentele waaiers vergelyk goed met die verwysingswaaier en bevredig die ontwerpsdoelwitte.

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Acknowledgements

The author expresses his gratitude to the following organizations and individuals for their contributions to this study :

Howden-Safanco for providing funding.

Prof. T.W. von Backstrom for his guidance and forbearance. Dr. S.J. Venter for advice regarding the test facility and instrumentation.

My friends, colleagues and teachers; Dave, Paul, Jeff and Theo for their example and inspiration.

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Table of Contents Declaration i. Abstract ii. opsomming iii. Acknowledgements iv. Contents v. List of Tables x.

List of Figures xi.

Nomenclature xv.

1 INTRODUCTION 1

2 LITERATURE SURVEY AND REVIEW OF FAN DESIGN PROCEDURES 5

2.1 The Fan Design Problem 7

2.1.1 Nomenclature 8

2.1.2 Fan Design 9

2.1.3 Fan Performance 16

2.1.3.1 Fan Pressures 16

2.1.3.2 Efficiency 19

3 RADIAL EQUILIBRIUM AND VORTEX DISTRIBUTIONS 20

3.1 Radial Equilibrium 20

3.2 The simple Radial Equilibrium Equations 24

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3.3 Radial Velocity Triangle Variations

3.4 Swirl Velocity Distributions

3.4.1

Free Vortex

3.4.2

Non Free Vortex Distributions

4 DESIGN METHOD

4.1

Design Specification and Constraints

4.2

optimisation of the Vortex Distribution and

HUb-tip ratio

26 28 28 29 31 31

33

4.2.1

FANVTX

34 4.2.1.1

Input Specification

35

4.2.1.2

Preliminary Calculations and Deduced

36

Parameters

4.2.1.3

Axial Exit Velocity Distribution

36 4.2.1.4

Calculation of Flow Parameters

38 4.2.1.5

Streamline Shift and Curvature

41

4.2.2

FANOPT

43 4.3

Blade Design

44 4.3.1

FANBLD

44 4.3.1.1

Input Specification

45 4.3.1.2 Blading Parameters 46 4.3.1.3

Blading Efficiency

48 4.3.1.4

Blade Co-ordinates

50 4.4

Design Discussion

50

4.4.1

Evaluation of Vortex Distribution and HUb-tip

50

ratio

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4.4.2 Blade Design 4.5 Fan Manufacture

4.5.1 Blades 4.5.2 Hub

5 EXPERIMENTAL EVALUATION

5.1 Test Facility and Instrumentation 5.1.1 Test Facility

5.1.2 Instrumentation

5.2 Test Procedure and Data Processing 5.2.1 Test Procedure 5.2.2 Data Processing 5.3 Experimental Results 5.3.1 Facility Qualification 5.3.2 V Fan Characteristics 5.3.3 B Fan Characteristics

5.3.4 Discussion of the Experimental Results

6 CONCLUSIONS AND RECOMMENDATIONS 6.1 Conclusions

6.2 Recommendations

FIGURES AND TABLES

APPENDIX A DERIVATION OF THE EXIT AXIAL VELOCITY EQUATIONS

vii

_,I 53 55 56 57 58 58 58 60 61 61 62 62 63 65 67 70 73 73 75 76 A.1

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APPENDIX B FAN OPTIMISATION

1.1 Van Niekerks' optimisation Method 1.2 Program FANOPT

1.3 Sample Calculations

APPENDIX C FAN BLADE DESIGN

1.1 Lift and Drag Coefficients 1.1.1 Lift Coefficient

1.1.2 Drag Coefficient

1.1.3 Losses and Efficiency

1.1.3.1 Overall Total Pressure Loss Coefficient 1.1.3.2 The Secondary Drag Coefficient

1.1.3.3 Efficiency Estimation 1.1.3.4 Tip Clearances

1.1.4 Blade Camber, Incidence and Flow Deflection 1.1.5 Blade Loading Factor Limits

1.1.5.1 Low Solidity Blading 1.1.5.2 High solidity Blading

APPENDIX D FAN PERFORMANCE AND DATA PROCESSING 1.1 The Fan Laws and Data Scaling

1.2 Program FANDAP - Fan Data Processing 1.3 Sample Calculations APPENDIX E CALIBRATION viii B.1 B.1 B.10 B.12 C.1 C.1 C.2 C.5 C.G C.S C.10 C.11 C.12 C.12 C.14 C.15 C.1G D.1 D.1 D.2 D.7 E.1

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1.1 Inlet Bellmouth E.1

1.2 System Air Leakage E.2

1.3 Plenum Chamber Velocity Profile E.2

1.4 Torque Transducer E.3

1.5 Pressure Transducers E.3

1.6 Rotational Speed E.4

APPENDIX F ACTUATOR DISC THEORY

REFERENCES

ix

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