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Computation of the Stability Limit of Nonlinear Bladerow Flutter with a Fully Coupled Frequency Domain FSI Solver

Berthold, Christian and Gross, Johann and Frey, Christian and Krack, Malte (2019) Computation of the Stability Limit of Nonlinear Bladerow Flutter with a Fully Coupled Frequency Domain FSI Solver. In: Proceedings of 8th GACM Colloquium on Computational Mechanics, pp. 311-314. kassel university press. 8th GACM Colloquium on Computational Mechanics, 28-30 Aug 2019, Kassel. ISSN 978-3-7376-5093-9

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Official URL: https://www.upress.uni-kassel.de/katalog/abstract.php?978-3-7376-5093-9

Abstract

To guarantee a safe operation of turbomachinery components engineers need to consider the aeroe- lastic behavior of the mechanical design. Due to increasing demands with respect to e�ciency and fuel consumption components need to be further optimized. However conventional computational analysis meth- ods for aeroelasticity which are commonly used in industry during the design phase have uncertainties since they are often based on linearization or neglect interactions between physical nonlinear e�ects in the solid and �uid domain. Thus large safety margins for conventional methods need to be considered resulting in restrictive design guidelines. Furthermore the nonlinear behavior of blade vibrations and the interaction with the surrounding nonlinear �ow is only rarely analyzed and therefore not yet fully understood. Time accurate methods can deliver higher accuracy but the computational costs are prohibitive for the industrial design pro- cess. In this study a fully coupled �uid-structure interaction (FSI) solver in the frequency domain is presented to provide a computationally e�cient simulation tool which is able to consider nonlinear solid and �uid e�ects of blade limit cycle oscillations (LCOs) in turbo engines. It can compute stable LCOs as well as unstable LCOs (stability limit) which can occur e.g. due to dry nonlinear friction in shrouded blades and is based on the Harmonic Balance method. The fourier components of the blade vibration and the frequency are passed to the �ow solver and the aerodynamic forces are returned to the strucure solver. Because the frequency of self excited vibrations is not known a priori the FSI solver considers the frequency as part of the sought solution. Furthermore a linearization of the aerodynamic forces inside the structure solver is introduced to improve the convergence of the coupled solver and countermeasures are implemented to prevent the solver from converging to the trivial solution (zero amplitude). To further reduce the computational costs the structural model is reduced with the Craig-Bampton approach. During the reduction the degrees of freedom in the solid contact regions of the bladerow are retained to model dry friction. To initialize the solver the energy method is extended to approximately determine the nonlinear behavior with a one-way coupling approach. The novel method is applied to a bladerow which is aerodynamically stable for small vibration amplitudes. With in- creasing amplitude the modeshape as well as the frequency change due to nonlinear friction in the joints of the shrouded rotor. This has an e�ect on the aerodynamic response and for large amplitudes the oscillations are aerodynamically unstable. The coupled solver is able to determine the limit of stability and the frequency of the coupled problem while conventional energy methods are not able to detect a stability boundary at all.

Item URL in elib:https://elib.dlr.de/134032/
Document Type:Conference or Workshop Item (Keynote)
Title:Computation of the Stability Limit of Nonlinear Bladerow Flutter with a Fully Coupled Frequency Domain FSI Solver
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Berthold, ChristianChristian.Berthold (at) dlr.deUNSPECIFIED
Gross, JohannUNSPECIFIEDUNSPECIFIED
Frey, ChristianChristian.Frey (at) dlr.deUNSPECIFIED
Krack, MalteUNSPECIFIEDUNSPECIFIED
Date:2019
Journal or Publication Title:Proceedings of 8th GACM Colloquium on Computational Mechanics
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Page Range:pp. 311-314
Editors:
EditorsEmailEditor's ORCID iD
Gleim, TobiasUNSPECIFIEDUNSPECIFIED
Lange, StephanUNSPECIFIEDUNSPECIFIED
Publisher:kassel university press
ISSN:978-3-7376-5093-9
Status:Published
Keywords:fluid-structure interaction, harmonic balance, flutter, aeroelasticity, shrouded turbine, dry friction
Event Title:8th GACM Colloquium on Computational Mechanics
Event Location:Kassel
Event Type:international Conference
Event Dates:28-30 Aug 2019
HGF - Research field:Energy
HGF - Program:Energy Efficiency, Materials and Resources
HGF - Program Themes:Efficient and Flexible Power Plants
DLR - Research area:Energy
DLR - Program:E VS - Combustion Systems
DLR - Research theme (Project):E - Gas Turbine
Location: Köln-Porz
Institutes and Institutions:Institute of Propulsion Technology > Numerical Methodes
Deposited By: Berthold, Christian
Deposited On:10 Feb 2020 08:01
Last Modified:10 Feb 2020 09:10

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