computation of the vibration of a whole aero-engine model with nonlinear bearings

203 Pages·2012·10.09 MB·English

The University of Manchester Research
Computation of the Vibration of a Whole Aero-Engine
Model with Nonlinear Bearings
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Citation for published version (APA):
Pham, P. (2010). Computation of the Vibration of a Whole Aero-Engine Model with Nonlinear Bearings. [Doctoral
Thesis, The University of Manchester]. University of Manchester.
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Download date:08. Jan. 2023
COMPUTATION OF THE VIBRATION OF A
WHOLE AERO-ENGINE MODEL WITH
NONLINEAR BEARINGS

A thesis submitted to The University of Manchester for the degree of
Doctor of Philosophy
in the Faculty of Engineering and Physical Sciences

2010

PHAM MINH HAI

SCHOOL OF MECHANICAL, AEROSPACE AND CIVIL ENGINEERING
CONTENTS

TITLE PAGE 1
CONTENTS 2
GLOSSARY OF TERMS 7
LIST OF FIGURES 14
LIST OF TABLES 19
ABSTRACT 20
DECLARATION 21
COPYRIGHT STATEMENT 22
ACKNOWLEDGMENTS 23

1 INTRODUCTION 24
1.1 SUMMARY OF THESIS OBJECTIVES AND CONTRIBUTIONS 28
1.2 SUMMARY OF THESIS STRUCTURE 30
FIGURES 32

2 REVIEW OF PREVIOUS RESEARCH 35
2.1 INTRODUCTION 35
2.2 SOLUTION TECHNIQUES FOR THE UNBALANCE RESPONSE 35
2.2.1 Time Domain Techniques 36
2.2.2 Frequency Domain Techniques 40
2.3 NONLINEAR PHENOMENA IN SFD ROTOR-BEARING 43
SYSTEMS
2.4 THE SFD MODEL 45
2.5 PARAMETERIC STUDIES ON SFD ROTOR-BEARING 52
SYSTEMS

2
2.6 CONCLUSIONS 53
FIGURE 54

3 THE IMPULSIVE RECEPTANCE METHOD 55
3.1 INTRODUCTION 55
3.2 THEORY 57
3.2.1 Outline 57
3.2.2 Modification for Rigid Body Modes 60
3.2.3 Inclusion of the Gyroscopic Effect 62
3.3 SIMULATIONS 65
3.3.1 Linear Pre-Processing 65
3.3.2 Nonlinear Computation for the Unbalance Response 66
3.3.2.1 Testing and Validation of IRM 67
3.3.2.2 Some Preliminary Results of a Parametric Analysis 69
3.4 CONCLUSIONS 70
FIGURES 71

4 A COMPUTATIONAL INVESTIGATION INTO 76
THE USE OF THE NEWMARK-BETA METHOD
FOR WHOLE-ENGINE ANALYSIS

4.1 INTRODUCTION 76
4.2 FAST NEWMARK-BETA METHOD (FNBM) 77
4.3 DISCUSSION 79
4.4 CONCLUSIONS 81
FIGURES 82

5 A WHOLE-ENGINE RHBM 84

5.1 INTRODUCTION 84

3
5.2 THEORY 85
5.2.1 System Description 85
5.2.2 Derivation of the Block of Dynamic Equations 89
5.2.3 Derivation of the Block of Pseudo-Static Equations 93
5.2.4 Solution of the Equations 96
5.2.5 Recovery of the Full Set of Degrees of Freedom 98
5.2.6 Some Observations 99
5.3 SIMULATIONS 99
5.3.1 Linear Pre-Processing 100
5.3.2 Nonlinear Computation for the Unbalance Response 100
5.3.2.1 Case A: SFU 101
5.3.2.2 Case B: MFU 102
5.3.2.3 Discussion 103
5.4 CONCLUSIONS 105
FIGURES 107

6 A COMPUTATIONAL PARAMETRIC ANALYSIS 115
OF THE VIBRATION OF A THREE-SPOOL AERO-
ENGINE UNDER MULTI-FREQUENCY
UNBALANCE EXCITATION

6.1 INTRODUCTION 115
6.2 DESCRIPTION OF WHOLE-ENGINE MODEL 117
6.2.1 Linear Pre-processing 118
6.2.2 Non-linear computation for unbalance response 119
6.3 SIMULATION RESULTS 121
6.3.1 Speed Response through Time-domain Solution 121
6.3.1.1 ‘Unsealed’ Case, no bump-springs, ‘Co-phased’ unbalances 122
6.3.1.2 ‘Slightly sealed’ (no bump-springs) versus ‘Unsealed’ (no 124
bump-springs)
6.3.1.3 ‘Co-phased’ versus ‘Anti-phased’ unbalances (no bump 124

4
springs)
6.3.1.4 Use of bump-springs on LP rotor’s SFD bearings 125
6.3.1.5 Note on computation time 126
6.3.2 Application of RHBM – non-constant speed ratio 127
6.4 CONCLUSIONS 129
FIGURES 131

7 A PARAMETRIC ANALYSIS OF UNBALANCE 145
RESPONSE OF A REAL TWIN-SPOOL AERO-
ENGINE
7.1 INTRODUCTION 145
7.2 DESCRIPTION OF TEST ENGINE 146
7.2.1 Overview 147
7.2.2 Structural Model 148
7.3 PARAMETRIC ANALYSIS – UNDAMPED LINEAR PART 148
7.3.1 Aligned Bearing Housings 149
7.3.2 Effect of SFD-housing misalignment 152
7.4 PARAMETRIC ANALYSIS – PROPORTIONALLY DAMPED 152
LINEAR PART
7.4.1 Theory 153
7.4.2 Computational Validation of proportionally-damped IRM 156
7.4.3 Unbalance response of proportionally-damped engine structure 158
7.5 CONCLUSIONS 159
FIGURES 161

8 CONCLUSIONS AND PROPOSALS FOR FUTURE 185

RESEARCH

8.1 CONCLUSIONS 185
8.2 PROPOSALS FOR FUTURE RESEARCH 188

5
9 REFERENCES 191

APPENDICES 198
A1 “-theory” MODEL FOR SFD 198
A2 ASSEMBLY OF MATRICES ρ z, ρk z, ρk z 200
cos sin
A3 VALIDATION OF THE FAST NEWMARK-Beta METHOD 201
Word count: 33793

6
GLOSSARY OF TERMS

DEFINITION OF COMMON USED TERMS

Journal Ring fixed to the outer race of a rolling-element bearing and
mechanically prevented from rotating ralative to the shaft axis.
Forms inner surface of SFD.
Linear part The system minus the squeeze film dampers.
Non-linear degree of Those degrees of freedom of the linear part that are associated with
freedom the nonlinear forces.
Receptance Frequency response function that, for a given frequency, relates the
force/moment applied in the direction of one degree of freedom with
the consequent displacement response on another degree of
freedom.
Sprung SFD SFD with a parallel retainer spring.
Squeeze film damper Annulus of oil filling the clearance between the journal and the
(SFD) inner surface of the bearing housing.
State space A space that is used to specify the instantaneous values of the
dynamical variables (displacements and velocities) and (for a forced
system) the associated value of the independent variable (i.e. time).
Unsupported SFD An unsprung SFD in which the journal is fully eccentric within the
radial clearance under the static load in the static condition.
Whole-engine model A mathematical model of the structure of an aero-engine (multi-
shaft), whose principal constitutions include rotors supported on one
casing via SFD (s).

7
COMMONLY USED ABBREVIATIONS

FE Finite element
iLP, iIP, iHP The frequency components whose frequencies are equal to the i-th
multiples of the roational speeds of LP-, IP- and HP-rotors
respectively
IRM Impulsive Receptance Method (Chapter 3)
RHBM Receptance Harmonic Balance Method (Chapter 5)
SFD Squeeze film damper
NH The nominal rotational speed of the HP rotor (Chapter 7)

LIST OF SYMBOLS FOR PRINCIPAL PARAMETERS

The following list is not exhaustive. However, all parameters are defined in the main text.
Greek letter symbols are listed towards the end. Vector and matrices are in bold typeface
(vector in lower case and matrices in upper case).

a, b a  a T, b  b T
1 n 1 n

a b ab  a b T
1 1 n n

a b a /b  a /b T
1 1 n n
p ap  apT
a 1 n
sina, cosa, sina  sina T, cosa  cosa T,
1 n 1 n
 
exp a exp(a )  exp(a )T
1 n
A  accelerance matrices, eqs (5.27a, b)
J v
sel
Bk matrix, eq. (5.24b)

8
C , C ,… receptance matrices, eqs. (5.17a-g)
JJ vv
~ ~
    “incomplete” receptance matrices, eq. (5.34a, b)
C , C 
vv vw
Dk, Ek, matrices, eqs. (5.24a, 5.26a, b)
 
F k
f vector of squeeze-film forces, unbalance forces, static loading
(eq. (3.3))
f fx ,x ,t 
k k k k
g gT1  gTJT
 
g T
j      
j1 j1 jGj jGj
G total number of gyroscopic locations on rotor no. j
j
H ,H ,H modal matrices defined in eqs. (3.2, 3.5, 3.18, 3.19, 3.28)
f x g
 ~ ~
“incomplete” modal matrices defined by eqs. (5.33, 5.41b, c)
H , H ,H
v v w
h time step size and film thickness for Chapter 2 and Appendix A1
i counter for non-linear bearings
polar moment of inertia at gyroscopic location no. p of rotor no. j
I
jp
I identity matrix
j counter for rotors
J total number of rotors
k time-step counter in Chapter 3 and Chapter 4, counter for
harmonics in Chapter 5
K maximum of number of harmonics
L matrix defined by eq. (3.29a)
L matrix defined by eq. (5.25c)
j

9