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Analysis of Friction-Saturated Flutter Vibrations With a Fully Coupled Frequency Domain Method

Berthold, Christian and Gross, Johann and Frey, Christian and Krack, Malte (2021) Analysis of Friction-Saturated Flutter Vibrations With a Fully Coupled Frequency Domain Method. In: ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition, GT 2020. ASME Turbo Expo 2020, 21.-25. Sept. 2020, Virtual Conference. doi: 10.1115/GT2020-16253. ISBN 978-079188419-5.

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Flutter stability is a dominant design constraint of modern gas and steam turbines. Thus, flutter-tolerant designs are currently explored, where the resulting vibrations remain within acceptable bounds. In particular, friction damping has the potential to yield Limit Cycle Oscillations (LCOs) in the presence of a flutter instability. To predict such LCOs, it is the current practice to model the aerodynamic forces in terms of aerodynamic influence coefficients, derived for some normal modes of the linearized structural model and fixed oscillation frequency. However, this approach neglects that both the nonlinear contact interactions and the aerodynamic stiffness cause a change in the deflection shape and the frequency of the LCO. This, in turn, may have a substantial effect on the aerodynamic damping. The goal of this paper is to assess the technical importance of these neglected interactions. To this end, a state-of-the-art aero-elastic model of a low pressure turbine blade row is considered, undergoing nonlinear frictional contact interactions in the tip shroud interfaces. The LCOs are computed with a fully-coupled harmonic balance method, which iteratively computes the Fourier coefficients of structural deformation and conservative flow variables, as well as the a priori unknown frequency. The coupled algorithm was tested for various combinations of harmonics in both domains and found to provide excellent computational robustness and efficiency. Moreover, a refinement of the conventional energy method is developed and assessed, which accounts for both the nonlinear contact boundary conditions and the linearized aerodynamic influence. It is found that the conventional energy method may not predict a limit cycle oscillation at all while the novel approach presented here can. Furthermore the refined energy method provides deep understanding of the nonlinear aero-elastic interactions.

Item URL in elib:https://elib.dlr.de/140626/
Document Type:Conference or Workshop Item (Speech)
Title:Analysis of Friction-Saturated Flutter Vibrations With a Fully Coupled Frequency Domain Method
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Berthold, ChristianChristian.Berthold (at) dlr.deUNSPECIFIED
Gross, JohannUniversität StuttgartUNSPECIFIED
Frey, ChristianChristian.Frey (at) dlr.deUNSPECIFIED
Krack, MalteUniversität StuttgartUNSPECIFIED
Date:11 January 2021
Journal or Publication Title:ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition, GT 2020
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:No
DOI :10.1115/GT2020-16253
Keywords:Aeroelasticity, Fluid-Structure Interaction, Frequency Domain, Harmonic Balance, Limit Cycle Oscillation, Turbomachinery, Flutter
Event Title:ASME Turbo Expo 2020
Event Location:Virtual Conference
Event Type:international Conference
Event Dates:21.-25. Sept. 2020
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:propulsion systems
DLR - Research area:Aeronautics
DLR - Program:L ER - Engine Research
DLR - Research theme (Project):L - Virtual Engine and Validation methods (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Propulsion Technology > Numerical Methodes
Deposited By: Berthold, Christian
Deposited On:26 Jan 2021 09:00
Last Modified:09 Feb 2021 15:07

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