Rotor Dynamic Analysis of RM12 Jet Engine Rotor using ANSYS

103 Pages·2012·2.6 MB·English

Master's Degree Thesis
ISRN: BTH-AMT-EX--2012/D-10--SE

Rotor Dynamic Analysis of RM12

Jet Engine Rotor using ANSYS

Deepak Srikrishnanivas

Department of Mechanical Engineering
Blekinge Institute of Technology
Karlskrona, Sweden
2012

Supervisors: Gunnar Högström, Volvo Aero
Ansel Berghuvud, BTH

Rotor Dynamic Analysis of
RM12 Jet Engine Rotor
using ANSYS

Deepak Srikrishnanivas
Department of Mechanical Engineering
Blekinge Institute of Technology
Karlskrona, Sweden
2012

Thesis submitted for completion of Master of Science in Mechanical
Engineering with emphasis on Structural Mechanics at the Department of
Mechanical Engineering, Blekinge Institute of Technology, Karlskrona,
Sweden.
Abstract
Rotordynamics is a field under mechanics, mainly deals with the vibration
of rotating structures. In recent days, the study about rotordynamics has
gained more importance within Jet engine industries. The main reason is Jet
engine consists of many rotating parts constitutes a complex dynamic
system. While designing rotors of high speed turbo machineries, it is of
prime importance to consider rotordynamics characteristics in to account.
Considering these characteristics at the design phase may prevent the jet
engine from severe catastrophic failures. These rotordynamic
characteristics can be determined with the help of much relied Finite
element method. Traditionally, Rotordynamic analyses were performed
with specialized commercial tools. On the other hand capabilities of more
general FEA software has gradually been developed over the time. As such
developed and commonly used software is Ansys. The aim of this thesis
work is to build a RM12 Jet engine rotor model in Ansys and evaluate its
rotordynamic capabilities with the specialized rotordynamics tool, Dyrobes.
This work helps in understanding, modeling, simulation and post
processing techniques for rotordynamics analyses of RM12 Jet engine rotor
using Ansys.
Keywords:
Rotordynamics, RM12, Jet engine, Gas turbines, Ansys, Dyrobes,
Vibration, Rotor, Twin spool
Note: The RM12 Jet engine data contains confidential information.
Numerical values and results related to RM12 are not presented anywhere
in this public version of the report.
II
Acknowledgements
This thesis work is the final project presented for the Master of Science in
Mechanical engineering program with emphasis on Structural Mechanics at
Blekinge Institute of Technology, Karlskrona, Sweden.
This work was carried out from the month of March 2012 to August 2012
at Volvo Aero Corporation, Trollhättan, Sweden.
I would like to thank my supervisor, Mr. Gunnar Högström at Volvo Aero,
for his patient guidance, support and encouragement throughout my entire
work. At Blekinge Institute of Technology, I would like to thank my
supervisor, Dr. Ansel Bherguvud for his guidance and valuable feedback.
I would also like to thank my parents and friends for their support
throughout my studies, without which this work would not be possible.

Trollhättan, Sweden, August 2012
Deepak Srikrishnanivas

III
Contents
Abstract ........................................................................................................ II
List of Tables .............................................................................................. IX
Nomenclature ............................................................................................... X
1 Introduction .......................................................................................... 1
1.1 Aim and scope ................................................................................... 1
1.2 Background ....................................................................................... 1
1.3 Objectives of Rotordynamic analysis ................................................ 2
2 Literature Review ................................................................................. 3
2.1 Rotor vibrations ................................................................................ 3
2.1.1 Lateral rotor vibration .............................................................. 3
2.1.2 Torsional rotor vibration .......................................................... 3
2.1.3 Axial rotor vibration ................................................................. 3
2.2 Fundamental Equation ..................................................................... 4
2.3 Theory ............................................................................................... 5
2.3.1 Determination of natural frequencies ....................................... 7
2.3.2 Steady state response to unbalance .......................................... 7
2.4 Terminologies in Rotordynamics ...................................................... 8
2.4.1 Whirling .................................................................................... 8
2.4.2 Gyroscopic effect ...................................................................... 8
2.4.3 Damping .................................................................................. 10
2.4.4 Mode shapes ........................................................................... 10
2.4.5 Whirl Orbit .............................................................................. 12
2.4.6 Critical speed .......................................................................... 13
2.4.7 Campbell diagram .................................................................. 13

IV
3 Rotordynamic analysis in ANSYS ..................................................... 15
3.1 ANSYS frame of references ............................................................. 15
3.1.1 Equation of motion for Stationary reference frame ................ 15
3.1.2 Equation of motion for Rotating reference frame ................... 16
3.1.3 Stationary frame of reference Vs rotating frame of reference 16
3.2 Overview of rotordynamic analyses in ANSYS ............................... 17
3.3 Rotordynamic analyses and solution controls ................................ 17
3.3.1 Modal analysis without spin ................................................... 17
3.3.2 Critical speed and Campbell analysis .................................... 18
3.3.3 Unbalance response analysis .................................................. 19
3.4 Post processing in ANSYS ............................................................... 20
4 Verification of Test Model in ANSYS ............................................... 21
4.1 Simple rotor model – test case ........................................................ 21
4.2 FE model of the simple rotor .......................................................... 22
4.3 Boundary condition ......................................................................... 23
4.4 Analysis and result discussion ........................................................ 23
4.4.1 Modal analysis without spin ................................................... 23
4.4.2 Critical speed and Campbell analysis .................................... 23
4.4.3 Unbalance response analysis .................................................. 26
4.5 Conclusion ...................................................................................... 29
5 Modeling and analysis of RM12 Jet engine rotor ............................ 30
5.1 RM12 rotor system .......................................................................... 30
5.2 Selection of Elements ...................................................................... 31
5.2.1 BEAM188 ................................................................................ 31
5.2.2 MASS21 ................................................................................... 32
5.2.3 COMBI214 .............................................................................. 32
5.3 FE modeling .................................................................................... 33
5.3.1 Modeling of rotor .................................................................... 33
5.3.2 Modeling of blade mass .......................................................... 38
V
5.3.3 Modeling of bearings and support .......................................... 39
5.4 Material Properties ......................................................................... 43
5.5 LPS and HPS rotor component creation ........................................ 44
5.6 Loads ............................................................................................... 45
5.7 Constraints ...................................................................................... 46
5.8 Rotor summary ................................................................................ 47
6 Results and Discussions ..................................................................... 49
6.1.1 Modal analysis without spin ................................................... 49
6.1.2 Critical speed and Campbell diagram analysis ...................... 56
6.1.3 Unbalance response analysis .................................................. 60
7 A case study: potential improvement in modeling approach of RM12
68
7.1 RM12 rotor – case study model ...................................................... 68
7.2 Analysis and results ........................................................................ 71
8 Conclusion .......................................................................................... 74
9 Future work ........................................................................................ 77
References .................................................................................................. 78
Appendices ..................................................................................................... i
A.1 Ansys batch files for simple rotor model ............................................ i
A.1.1 Modal analysis without Gyroscopic effect ................................. i
A.1.2 Critical speed and campbell diagram analysis ......................... iii
A.1.3 Unbalance response analysis ................................................... vi
A.2 Postprocessing of unbalance response analysis .............................. ix
A.2.1 Calculation of displacement at particular node ..................... ix
A.2.2 Calculation of transmitted force through the bearing ............. ix
A.3 RM12 Ansys model – Numbering standards ...................................... x
VI
List of Figures
Figure 2-1. Generalized Laval-Jeffcott rotor model. ................................... 5
Figure 2-2. End view of Laval-Jeffcott rotor. ............................................... 6
Figure 2-3. Types of Whirling ....................................................................... 8
Figure 2-4. Gyroscopic effect ....................................................................... 9
Figure 2-5. Characteristics of cylindrical mode shape .............................. 11
Figure 2-6. Characteristics of conical mode shape .................................... 12
Figure 2-7. Whirl orbit ............................................................................... 13
Figure 2-8. Campbell diagram ................................................................... 14
Figure 4-1. Simple rotor model – test case ................................................. 21
Figure 4-2. FE model of simple rotor in Ansys .......................................... 22
Figure 4-3. Campbell diagram of simple rotor – from Ansys .................... 24
Figure 4-4. Campbell diagram of simple rotor – from Dyrobes ................ 25
Figure 4-5. Maximum response of the simple rotor – from Ansys ............. 26
Figure 4-6. Maximum response of the simple rotor – from Dyrobes ......... 27
Figure 4-7. Maximum bearing load of the simple rotor – from Ansys ....... 28
Figure 4-8. Maximum bearing load of the simple rotor – from Dyrobes ... 28
Figure 5-1. BEAM188 element. .................................................................. 31
Figure 5-2. MASS21 element. ..................................................................... 32
Figure 5-3. MASS21 element. ..................................................................... 33
Figure 5-4. RM12 Dyrobes model - LPS rotor discretization .................... 34
Figure 5-5. Different portions of FE rotor ................................................. 35
Figure 5-6. Tapered beam section – example ............................................. 37
Figure 5-7. Bearing and support connection .............................................. 39
Figure 5-8. Intermediate Bearing No.4 connection .................................... 41
Figure 5-9. FE model of RM12 engine rotor – expanded view .................. 42
Figure 5-10. FE model of RM12 engine rotor – cut section view .............. 43
Figure 5-11. LPS and HPS components of RM12 engine rotor ................. 45
Figure 5-12. Unbalance load distribution .................................................. 46
VII
Figure 5-13. Displacement constraints ...................................................... 47
Figure 5-14. Sectional view of RM12 rotor – Ansys model ........................ 47
Figure 5-15. Sectional view of RM12 rotor – Dyrobes model .................... 48
Figure 6-1. Mode shape 1 of RM12 rotor – from Ansys ............................. 51
Figure 6-2. Mode shape 1 of RM12 rotor – from Dyrobes......................... 51
Figure 6-3. Mode shape 2 of RM12 rotor – from Ansys ............................. 52
Figure 6-4. Mode shape 2 of RM12 rotor – from Dyrobes......................... 52
Figure 6-5. Mode shape 3 of RM12 rotor – from Ansys ............................. 53
Figure 6-6. Mode shape 3 of RM12 rotor – from Dyrobes......................... 53
Figure 6-7. Mode shape 4 of RM12 rotor – from Ansys ............................. 54
Figure 6-8. Mode shape 4 of RM12 rotor – from Dyrobes......................... 54
Figure 6-9. Mode shape 5 of RM12 rotor – from Ansys ............................. 55
Figure 6-10. Mode shape 5 of RM12 rotor – from Dyrobes....................... 55
Figure 6-11. Campbell diagram of RM12 rotor – from Ansys ................... 57
Figure 6-12. Campbell diagram of RM12 rotor – from Dyrobes ............... 58
Figure 6-13. Maximum response of RM12 rotor – from Ansys .................. 60
Figure 6-14. Maximum response of RM12 rotor – from Dyrobes .............. 61
Figure 6-15. Maximum bearing load of RM12 rotor – from Ansys ............ 62
Figure 6-16. Maximum bearing load of RM12 rotor – from Dyrobes ....... 62
Figure 6-17. Maximum displacement of RM12 rotor ................................. 64
Figure 6-18. Maximum displacement of RM12 rotor – expanded view ..... 65
Figure 6-19. Whirl orbit of RM12 rotor – from Ansys ............................... 66
Figure 6-20. Whirl orbit of RM12 rotor – from Dyrobes ........................... 66
Figure 7-1. FE model of RM12 rotor with 2D axisymmetric disk .............. 69
Figure 7-2. Modeling method of 2D axisymmetric Disk ............................ 70
Figure 7-3. Expanded view of RM12 rotor with 2D axisymmetric disk ..... 71
Figure 7-4. Campbell diagram of using 2D axisymmetric elements for
rotor-3 representation ................................................................................. 73
VIII