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Global Stability of rigid-body-motion fluid-structure-interaction problems
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Mechanics. Swedish e-Science Research Center (SeRC). (Stabilitet, Transition, Kontroll, Stability, Transition and Control)ORCID iD: 0000-0002-3344-9686
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Mechanics. Swedish e-Science Research Center (SeRC). (Stabilitet, Transition, Kontroll, Stability, Transition and Control)ORCID iD: 0000-0002-5913-5431
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0001-7864-3071
2019 (English)Report (Other academic)
Abstract [en]

A rigorous derivation and validation for linear fluid-structure-interaction (FSI) equations for a rigid-body-motion problem is performed in an Eulerian framework. We show that the “added-stiffness” terms arising in the formulation of Fanion et al. (2000) vanish at the FSI interface in a first-order approximation. Several numerical tests with rigid-body motion are performed to show the validity of the derived formulation by comparing the time evolution between the linear and non-linear equations when the base flow is perturbed by identical small-amplitude perturbations. In all cases both the growth rate and angular frequency of the instability matches within 0.1% accuracy. The derived formulation is used to investigate the phenomenon of symmetry breaking for a rotating cylinder with an attached splitter-plate. The results show that the onset of symmetry breaking can be explained by the existence of a zero-frequency linearly unstable mode of the coupled fluid-structure-interaction system. Finally, the structural sensitivity of the least stable eigenvalue is studied for an oscillating cylinder, which is found to change significantly when the fluid and structural frequencies are close to resonance.

Place, publisher, year, edition, pages
2019. , p. 38
Series
TRITA-SCI-RAP ; 2019:007
National Category
Fluid Mechanics and Acoustics Aerospace Engineering
Research subject
Aerospace Engineering
Identifiers
URN: urn:nbn:se:kth:diva-262856OAI: oai:DiVA.org:kth-262856DiVA, id: diva2:1365191
Funder
Swedish National Infrastructure for Computing (SNIC)
Note

QC 20191025. QC 20191030

Available from: 2019-10-23 Created: 2019-10-23 Last updated: 2019-10-30Bibliographically approved
In thesis
1. Stability and transition in pitching wings
Open this publication in new window or tab >>Stability and transition in pitching wings
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aeroelastic stability of airplanes is one of the most important aspects of airplane design. Flutter or divergence instabilities arising out of the interaction of fluid forces and structural elasticity must be avoided by design or through the limitation of the flight envelope. Classical unsteady theories have been established since the 1930s however, recent investigations with laminar wings and in transitional flows have found the theories to be unreliable in these regimes. The current work investigates the flow around unsteady airfoils in these flow regimes. A linear framework for the stability analysis of fluid-structure-interaction (FSI) problems is derived and validated. The derived formulation is then used to investigate the changes in the structural sensitivity of an eigenvalue for an oscillating cylinder, which is found to change significantly when the fluid and structural systems are close to resonance. The linear stability analysis is then applied to investigate the aeroelastic stability of a NACA0012 airfoil with a free pitch-deegree-of-freedom at transitional Reynolds numbers. The stability results of the coupled FSI system are found to be in good agreement with previously performed experimental results and were able to predict the onset of aeroelastic pitch-oscillations. The boundary layer evolution for a natural laminar flow airfoil undergoing forced small-amplitude pitch-oscillations is investigated at Rec = 7.5×105. Large changes in laminar-to-turbulent transition location are found throughout the pitch cycle which cause a non-linear aerodynamic force response. The origins of the non-linear unsteady aerodynamic response is explained on the basis of the phase-lagged quasi-steady evolution of the boundary layer. A simple empirical model is developed using the phase-lag concept to model the unsteady aerodynamic forces which fits the experimental data very well. On the other hand, the forced pitching investigation at Rec = 1.0×105 for the same airfoil found abrupt changes in transition during the pitch-cycle. A local stability analysis in the reverse flow region indicates that the stability characteristics of the LSB change character from convective to absolute, and it is conjectured that this change in stability characteristics may be the cause of abrupt changes inboundary-layertransition.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 54
Series
TRITA-SCI-FOU ; 2019:46
National Category
Aerospace Engineering Fluid Mechanics and Acoustics
Research subject
Aerospace Engineering; Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-262927 (URN)978-91-7873-348-4 (ISBN)
Public defence
2019-11-22, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Vinnova, 2014-00933EU, European Research Council, 694452-TRANSEP-ERC-2015- AdGSwedish e‐Science Research Center
Note

QC 20191028

Available from: 2019-10-28 Created: 2019-10-25 Last updated: 2019-10-30Bibliographically approved

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