Belesiotis, Panagiotis
(2022)
Methods for the Investigation of Transonic Buffet.
Doctor of Philosophy thesis, University of Liverpool.
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Abstract
Transonic buffet is an unsteady shock-wave/boundary-layer interaction phenomenon, encountered in large civil or military aircraft at edge-of-the-envelope conditions. The interaction of the unsteady aerodynamic loads with the elastic wing structure can pose a risk of structural failure and thus the absence of any structural vibration or buffeting at cruise conditions is a certification requirement by regulatory authorities. A thorough understanding of the mechanisms that govern the phenomenon is of paramount importance in order to face the engineering challenges that are associated with designing future wings that push the limits of the flight envelope. This present work aims to address the interaction of the phenomenon with wing vibration and to investigate the effect of transient growth on aerofoil transonic buffet. This is achieved by performing three different but related studies. The first one focuses on harmonically exciting the flow at steady and unsteady conditions. It is found that in contrast to aerofoil shock-buffet, that demonstrates full synchronisation to the excitation for certain combinations of excitation frequency and amplitude, the harmonic excitation of the wing only affects the high-frequency behaviour of the phenomenon associated with a global mode, while the low frequency behaviour remains unaffected. For the second study, a coupled fluid-structure simulation was carried out at unsteady conditions. This revealed that, while the initial linear structural response depends on the buffet frequency for all modes, this only holds for structural modes with natural frequencies close to that of buffet in the nonlinear part of the response. A dependence on their respective wind-off structural frequency and the first bending mode is found for lower frequency structural modes in the nonlinear part of the response. For the last study, transient growth analysis is applied at a supercritical aerofoil in steady and unsteady conditions. To the best of the author's knowledge, this is the first transient growth study on an aerofoil in transonic flow subject to shock buffet. Modest growth of optimal initial perturbations is observed. A quartic dependence of the maximum energy attained on the angle of attack is found for pre-onset conditions. These findings will help advance the understanding of the underlying physics of transonic buffet and ultimately inform future wing design.
| Item Type: | Thesis (Doctor of Philosophy) |
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| Divisions: | Faculty of Science and Engineering > School of Engineering |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 13 Nov 2023 14:43 |
| Last Modified: | 13 Nov 2023 14:43 |
| DOI: | 10.17638/03176709 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3176709 |
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