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Numerical Methods for Turbomachinery Aeromechanical Predictions
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. (Turbomachinery Aeromechanics)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In both aviation and power generation, gas turbines are used as key components. An important driver of technological advance in gas turbines is the race towards environmentally friendly machines, decreasing the fuel burn, community noise and NOx emissions. Engine modifications that lead to propulsion efficiency improvements whilst maintaining minimum weight have led to having fewer stages and lower blade counts, reduced distance between blade rows, thinner and lighter components, highly three dimensional blade designs and the introduction of integrally bladed disks (blisks). These changes result in increasing challenges concerning the structural integrity of the engine. In particular for blisks, the absence of friction at the blade to disk connections decreases dramatically the damping sources, resulting in designs that rely mainly on aerodynamic damping. On the other hand, new open rotor concepts result in low blade-to-air mass ratios, increasing the influence of the surrounding flow on the vibration response.

 

This work presents the development and validation of a numerical tool for aeromechanical analysis of turbomachinery (AROMA - Aeroelastic Reduced Order Modeling Analyses), here applied to an industrial transonic compressor blisk. The tool is based on the integration of results from external Computational Fluid Dynamics (CFD) and Finite Element (FE) solvers with mistuning considerations, having as final outputs the stability curve (flutter analysis) and the fatigue risk (forced response analysis). The first part of the study aims at tracking different uncertainties along the numerical aeromechanical prediction chain. The amplitude predictions at two inlet guide vane setups are compared with experimental tip timing data. The analysis considers aerodynamic damping and forcing from 3D unsteady Navier Stokes solvers. Furthermore, in-vacuo mistuning analyses using Reduced Order Modeling (ROM) are performed in order to determine the maximum amplitude magnification expected. Results show that the largest uncertainties are from the unsteady aerodynamics predictions, in which the aerodynamic damping and forcing estimations are most critical. On the other hand, the structural dynamic models seem to capture well the vibration response and mistuning effects.

 

The second part of the study proposes a new method for aerodynamically coupled analysis: the Multimode Least Square (MLS) method. It is based on the generation of distributed aerodynamic matrices that can represent the aeroelastic behavior of different mode-families. The matrices are produced from blade motion unsteady forces at different mode-shapes fitted in terms of least square approximations. In this sense, tuned or mistuned interacting mode families can be represented. In order to reduce the domain size, a static condensation technique is implemented. This type of model permits forced response prediction including the effects of mistuning on both the aerodynamic damping as well as on the structural mode localization. A key feature of the model is that it opens up for considerations of responding mode-shapes different to the in-vacuo ones and allows aeroelastic predictions over a wide frequency range, suitable for new design concepts and parametric studies.

Place, publisher, year, edition, pages
Stockholm: Royal Institute of Technology , 2011. , 127 p.
Series
Trita-KRV, ISSN 1100-7990 ; 11:08
Keyword [en]
Aeromechanics, numerical tools, methods, turbomachinery, aeroelasticity, gas turbines, vibrations
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-48418ISBN: 978-91-7501-135-6 (print)OAI: oai:DiVA.org:kth-48418DiVA: diva2:457544
Public defence
2011-12-15, M2, Brinellvägen 64, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Turbopower, AROMA
Note
QC 20111125Available from: 2011-11-25 Created: 2011-11-18 Last updated: 2011-11-25Bibliographically approved
List of papers
1. Effect of Scaling of Blade Row Sectors on the Prediction of Aerodynamic Forcing in a Highly Loaded Transonic Compressor Stage
Open this publication in new window or tab >>Effect of Scaling of Blade Row Sectors on the Prediction of Aerodynamic Forcing in a Highly Loaded Transonic Compressor Stage
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2011 (English)In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 133, no 2, 021013- p.Article in journal (Refereed) Published
Abstract [en]

An investigation of the sensitivity of a geometrical scaling technique on the blade forcing prediction and mode excitability has been performed. A stage of a transonic compressor is employed as a test object. A scaling ratio is defined, which indicates the amount of scaling from the original geometry. Different scaling ratios are selected and 3D Navier-Stokes unsteady calculations completed for each scaled configuration. A full-annulus calculation (nonscaled) is performed serving as reference. The quantity of interest is the generalized force, which gives a direct indication of the mode excitability. In order to capture both up- and downstream excitation effects, the mode excitability has been assessed on both rotor and stator blades. The results show that the first harmonic excitation can be predicted well for both up-and downstream excitations using moderate amounts of scaling. On the other hand, the predictions of second harmonic quantities do show a higher sensitivity to scaling for the investigated test case.

Keyword
Blade row, First harmonic, Generalized force, Geometrical scaling, Navier Stokes, Quantity of interest, Scaling ratio, Second harmonics, Stator blade, Test case, Test object, Transonic compressor, Compressors
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-27067 (URN)10.1115/1.4000579 (DOI)000283741600013 ()2-s2.0-77958571818 (Scopus ID)
Note
QC 20101210Available from: 2010-12-10 Created: 2010-12-06 Last updated: 2017-12-11Bibliographically approved
2. Numerical tool for prediction of aeromechanical phenomena in gas turbines
Open this publication in new window or tab >>Numerical tool for prediction of aeromechanical phenomena in gas turbines
2009 (English)In: 19th ISABE Conference / [ed] ISABE, Montreal: American Institute of Aeronautics and Astronautics Inc. , 2009, 1-11 p.Conference paper, Published paper (Refereed)
Abstract [en]

A numerical tool for aeromechanic design is presented. The output of the tool is the fatigue risk of the critical blade obtained by the Haigh diagram, and stability curves for the stability analyses. The tool integrates results from commercial Computational Fluid Dynamics (CFD) and Finite Element (FE) solvers. It uses a Reduced Order Modeling (ROM) technique in order to account for mistuning effects in an efficient way. The description of the numerical tool and an overview of typical results are presented in this paper. The applicability of the tool in the industrial design process is discussed as well as the outlook of the targeted capabilities.

Place, publisher, year, edition, pages
Montreal: American Institute of Aeronautics and Astronautics Inc., 2009
Keyword
aeromechanical design, fluid-structure interaction, ROM, mistuning, aerodynamic damping, unsteady forces, aerodynamic forcing, blade row interactiong, High Cycle Fatigue, CFD, FEM, Turbomachinery, Aeroelasticity
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-11959 (URN)
Conference
ISABE 2009
Projects
AROMATurbopower (TurboVib)
Note

QC 20110324

Available from: 2010-02-08 Created: 2010-01-29 Last updated: 2017-03-24Bibliographically approved
3. A New Reduced Order Modeling for Stability and Forced Response Analysis of Aero-Coupled Blades Considering Various Mode Families
Open this publication in new window or tab >>A New Reduced Order Modeling for Stability and Forced Response Analysis of Aero-Coupled Blades Considering Various Mode Families
2010 (English)In: Proceedings of ASME Turbo Expo 2010: Scottish Exhibition & Conference Centre / [ed] ASME 2010, Glasgow, UK: ASME 2010 , 2010, 1-10 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the description and application of a new method for stability and forced response analyses of aerodynamically coupled blades considering the interaction of various mode families. The method, here referred as MLS (Multimode Least Square), considers the unsteady forces due to the blade motion at different modes shape families and calculates the aerodynamic matrixes by means of a least square (L2) approximations. This approach permits the prediction of mode families’ interaction with capabilities of structural, aerodynamic and force mistuning. A projection technique is implemented in order to reduce the computational domain. Application of the method on tuned and structural mistuned forced response and stability analyses is presented on a highly loaded transonic compressor blade. When considering structural mistuning the forced response amplitude magnification is highly affected by the change in aerodynamic damping due to mistuning. Analyses of structural mistuning without aerodynamic coupling might result in over-estimated or under-estimated response when the source of damping is mainly aerodynamic. The frequency split due to mistuning can cause that mode families’ interact due to reducing their frequencies separation. The advantage of the present method is that the effect of mode family interaction on aerodynamic damping and forced response is captured not being restricted to single mode families.

Place, publisher, year, edition, pages
Glasgow, UK: ASME 2010, 2010
Series
GT2010, GT2010-22745
Keyword
aerodynamic damping, stability, flutter, forced response, ROM, aerodynamic coupling, mode family interaction, CFD, FE, Turbomachinery, aeromechanic desing
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-11991 (URN)10.1115/GT2010-22745 (DOI)000290927800122 ()2-s2.0-82055201355 (Scopus ID)978-0-7918-4401-4 (ISBN)
Conference
ASME Turbo Expo 2010
Projects
TurbopowerAROMA
Note

QC 20110211

Available from: 2010-02-08 Created: 2010-02-08 Last updated: 2012-09-05Bibliographically approved
4. Prediction of Turbomachinery Aeroelastic Behavior from a Set of Representative Modes
Open this publication in new window or tab >>Prediction of Turbomachinery Aeroelastic Behavior from a Set of Representative Modes
2012 (English)In: Proceedings of the ASME Turbo Expo 2011, Vol 6, Parts And B / [ed] Presented by ASME International Gas Turbine Institute, Vancouver, Canada: American Society of Mechanical Engineers , 2012, 1449-1461 p.Conference paper, Published paper (Refereed)
Abstract [en]

A method is proposed for the determination of the aeroelastic behavior of a system responding to mode-shapes different to the tuned in-vacuo ones, due to mistuning, mode family interaction or any other source of mode-shape perturbation. The method is based on the generation of a data base of unsteady aerodynamic forces arising from the motion of arbitrary modes and uses Least Square approximations for the prediction of any responding mode. The use of a reduced order technique allows for mistuning analyses and is also applied for the selection of a limited number of arbitrary modes. The application on a transonic compressor blade shows that the method captures well the aeroelastic properties in a wide frequency range. A discussion of the influence of the mode-shapes and frequency on the final stability response is also provided.

Place, publisher, year, edition, pages
Vancouver, Canada: American Society of Mechanical Engineers, 2012
Keyword
aeromechanics, aeroelasticity, stability, flutter, turbomachinery, methods
National Category
Mechanical Engineering
Research subject
SRA - Energy; Järnvägsgruppen - Ljud och vibrationer
Identifiers
urn:nbn:se:kth:diva-48896 (URN)10.1115/GT2011-46690 (DOI)000321160200141 ()2-s2.0-84865519323 (Scopus ID)978-0-7918-5466-2 (ISBN)
Conference
ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition, GT2011; Vancouver, BC, Canada, 6 June-10 June, 2011
Projects
Turbopower
Funder
StandUp
Note

QC 20111125

Available from: 2011-11-24 Created: 2011-11-24 Last updated: 2014-10-03Bibliographically approved
5. Uncertainty of forced response numerical predictions of an industrial blisk - Comparison with experiments
Open this publication in new window or tab >>Uncertainty of forced response numerical predictions of an industrial blisk - Comparison with experiments
Show others...
2012 (English)In: Proceedings of the ASME Turbo Expo 2012: Volume 7, Issue PARTS A AND B, 2012, ASME Press, 2012, 1537-1548 p.Conference paper, Published paper (Refereed)
Abstract [en]

Numerical methods, both Computational Fluid Dynamics (CFD) as well as Finite Elements (FE) methods, are widely used in industry with the purpose of predicting potential fatigue problems early in the design process. However, the uncertainty of such predictions is not clearly identified. The present paper presents the prediction of the vibration response of a rotor blisk part of 1 1/2 transonic compressor stage with comparison with experiments. Different uncertainty sources along the numerical aeromechanical chain are then identified. CFD solvers are employed for the prediction of both blade row interaction forces as well as the aerodynamic damping determination. Mistuning is assessed by the use of Reduced Order Modeling analyses and results compared with tip timing data. The peak amplitude response of a resonance mode of interest is determined for two different inlet conditions and thus the accuracy dependence on the excitation level is discussed. Results show that the largest uncertainties come from the unsteady aerodynamics, in which both aerodynamic damping and forcing estimations are critical. The structural dynamic models seem to capture the vibration response and mistuning effects well. Additionally, the challenges of tip timing data processing for detailed one-to-one validation of the tools are highlighted.

Place, publisher, year, edition, pages
ASME Press, 2012
Keyword
Aerodynamics, Computational fluid dynamics, Damping, Data processing, Exhibitions, Experiments, Gas turbines, Structural dynamics
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-49073 (URN)10.1115/GT2012-69534 (DOI)000335868800152 ()2-s2.0-84881187219 (Scopus ID)978-079184473-1 (ISBN)
Conference
ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, GT 2012; Copenhagen; Denmark; 11 June 2012 through 15 June 2012
Note

QC 20131007. Updated from submitted to published.

Available from: 2011-11-25 Created: 2011-11-25 Last updated: 2014-10-08Bibliographically approved

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Permanent link

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Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf