Masini, Luke 
ORCID: 0000-0001-5495-1627
(2021)
On Transonic Wing Shock Unsteadiness.
PhD thesis, University of Liverpool.
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Abstract
Aircraft wings in high-speed flight experience detrimental flow unsteadiness. Its interaction with the flexible wing structure and resulting dynamic loads are addressed in the certification specifications which stipulate a cruise design point free from any structural vibration and buffeting. One such flow unsteadiness is shock buffet and its inherent dynamics near the onset of unsteadiness are addressed herein. Specifically, an extensive experimental dataset of a large aircraft wing geometry and complementary scale-resolving simulations are scrutinised. Whilst the experimental dataset comprises a wide range of flow conditions from pre-onset to established buffet for Mach numbers between 0.70 and 0.84 and four configurations, the primary focus is on the clean wing at the design Mach number of 0.80 and Reynolds number of approximately 3.6 million (based on mean aerodynamic chord). Key to this study are highly-resolved unsteady surface pressure data acquired by dynamic pressure-sensitive paint, in addition to conventional data from pressure transducers and a wing-root strain gauge. To match the experiment and thereby aiding a richer elucidation of the flow physics, detached-eddy simulations are performed using two subgrid length-scale definitions, motivated by the challenge of simulating separating and reattaching shallow shear layers. Modal decomposition techniques are instrumental in pursuing a thorough data analysis. Experimentally, two distinct phenomena in shock-buffet conditions are identified. First, low-frequency shock unsteadiness with characteristic Strouhal numbers between 0.05 and 0.15 (where Strouhal number is based on mean aerodynamic chord and reference freestream velocity) propagates pressure disturbances predominantly inboard. Importantly, this coherent unsteadiness is exclusive to the experiment and even occurs before the strain gauge detects structural buffeting. Second, a broadband higher-frequency behaviour for Strouhal numbers between 0.2 and 0.5 is characterised by three-dimensional cellular patterns describing localised pockets of shear-layer pulsation synchronised with an outboard-propagating shock oscillation. Dominant modal features capturing this characteristic signature show striking similarity between experiment and simulation, detailing the pertinent attributes of shock-buffet unsteadiness whilst contrasting it with the first phenomenon. These findings will help clarify these edge-of-the-envelope flow phenomena and ultimately inform future wing design.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Science and Engineering > School of Engineering |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 28 Apr 2021 15:52 |
| Last Modified: | 18 Jan 2023 22:52 |
| DOI: | 10.17638/03119500 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3119500 |
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