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Forced Response Analysis of a Mistuned Blisk Using Noncyclic Reduced-Order Models
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. (Energy Technology)
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
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2018 (English)In: Journal of Propulsion and Power, ISSN 0748-4658, E-ISSN 1533-3876, Vol. 34, no 3, p. 565-577Article in journal (Refereed) Published
Abstract [en]

The importance of mistuning analysis lies on understanding the distribution of the vibrational energy around the blisk. The large vibration amplitudes of individual blades inherent in mistuned blisks reduces the high cycle fatigue margin significantly. It is therefore important to perform mistuning analyses at a high accuracy while keeping the computational cost at an acceptable level. Because numerous analyses with large amount of degrees of freedom models are commonly performed, it is frequent to employ reduced-order models such as to reduce the computational effort. In this paper, a unique way to address the reduced-order model is presented, where each blisk sector is attached as individual substructures with the free-interface approach known as Craig-Chang. This implementation is compared against a fixed-interface approach known as Craig-Bampton in terms of accuracy for disk- and blade-dominated modes. Neither of these approaches applies cyclic symmetry, making them more accurate in the presence of mistuning when the harmonic patterns are destroyed. Results show the high benefits of using the free-interface approach for a mistuned forced response analysis.

Place, publisher, year, edition, pages
2018. Vol. 34, no 3, p. 565-577
Keywords [en]
aeroelasticity, flutter, forced response, reduced order models, ROM, craig-bampton, craig-chang, noncyclic, cyclic symmetry, transformation, reduction subset nominal mode, snm, fixed-interface, free-interface
National Category
Aerospace Engineering
Research subject
Aerospace Engineering
Identifiers
URN: urn:nbn:se:kth:diva-227654DOI: 10.2514/1.B36584ISI: 000430384400001Scopus ID: 2-s2.0-85045754404OAI: oai:DiVA.org:kth-227654DiVA, id: diva2:1205004
Note

QC 20180514

Available from: 2018-05-09 Created: 2018-05-09 Last updated: 2018-05-15Bibliographically approved
In thesis
1. Development of Accurate Reduced Order Models in a Simulation Tool for Turbomachinery Aeromechanical Phenomena
Open this publication in new window or tab >>Development of Accurate Reduced Order Models in a Simulation Tool for Turbomachinery Aeromechanical Phenomena
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Modern gas turbines are still vulnerable to vibrations when operated at certain speeds. This unstable environment can lead to high cycle fatigue (HCF) and damage several of the components inside the turbine. Since engineers are striving to increase the turbines’ efficiency with thinner and more complex blade shapes, these critical speeds will always be present. For these reasons, aeromechanical analyses that is the study of structural and aerodynamic forces need to be assessed with a high level of accuracy. Since this type of analysis are very computational expensive, reduced order models (ROMs) are utilized to decrease the degrees of freedom (DoF) for a faster computation without compromising the accuracy. The present work focuses on cyclic and noncyclic ROMs implemented in an already existing aeroelastic tool, with different characteristics in their condensation and ease of usage depending on the analysis.

 

The AROMA (Aeroelastic Reduced Order Model Analysis) tool has been previously developed to predict the fatigue life of turbomachinery blades with the use of ROMs. The aim of this work has been to improve the tool in terms of accuracy, flexibility and speed, by employing additional reduction methods capable to predict forced responses analysis of large industrial-size models.

 

The understanding of an aeroelastic phenomena would not be complete if mistuning is not considered in the analysis. A mistuned bladed-disk means that all its sectors do not share the same mass and stiffness properties, which in reality this is the case. Mistuning can be addressed as probabilistic, taking into account the manufacturing tolerances and wear of the bladed disk, or it can be assessed as deterministic, also known as intentional mistuning.

 

The latter is achieved to increase the flutter stability by breaking the circumferential traveling waves modes due to energy confinement, and also to have a certain understanding of the forced response amplitude, which helps in designing for worst and best case scenarios.

 

The ROMs that have been incorporated in the AROMA tool are known as the component mode synthesis (CMS) and subset nominal mode (SNM) approaches. The CMS is split into two branches, these are the fixed- and freeinterface methods known as Craig-Bampton (CB) and Craig-Chang (CC), respectively. An intensive study with numerical and experimental validation has been performed for these three reduction methods. The outcome of the study is that each of these methods have their own drawbacks and benefits depending on the aeromechanical analysis problem. The SNM showed that it produces fast computations, with high level of accuracy when the mistuning level is low. On the other hand, a novel and unique approach, Craig-Chang multisubstructuring (CCMS), demonstrated fast computations and high accuracy when the mistuning level is high.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 68
Series
TRITA-ITM-AVL ; 2018:7
Keywords
flutter, forced response, high cycle fatigue, reduced order models, ROM, craig-bampton, mistuning, tuned, mistuned, cyclic, noncyclic, craig-chang, free-interface. fixed-interface, subset nominal mode, SNM, CBMS, CCMS, CCC, CBC, FEM, CMS, modal, eigen, modeshapes, aeroelasticity, aeromechanical, tool, turbomachinery, turbine, compressor, AROMA
National Category
Aerospace Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-227658 (URN)978-91-7729-750-5 (ISBN)
Public defence
2018-06-07, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20180514

Available from: 2018-05-14 Created: 2018-05-09 Last updated: 2018-05-15Bibliographically approved

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