Characterisation of backflow events over a wing section
Vinuesa R, Orlu R, Schlatter P (2017)
Publication Type: Journal article
Publication year: 2017
Journal
Book Volume: 18
Pages Range: 170-185
Journal Issue: 2
DOI: 10.1080/14685248.2016.1259626
Abstract
Rare backflow (negative wall-shear stress) events have recently been found and quantified in the near-wall region of canonical wall-bounded turbulent flows. Although their existence and correlation with large-scale events have been established beyond numerical and measurement technique uncertainties, their occurrence at numerically high Reynolds numbers is still rare (less than 1 per thousand and 1 per million at the wall and beyond the viscous sublayer, respectively). To better quantify these rare events, the turbulent boundary layer developing over the suction side of a wing section, experiencing an increasing adverse pressure gradient (APG) without separation along its chord c, is considered in the present work. We find that the backflow level of 0.06% documented in turbulent channels and zero-pressure-gradient (ZPG) turbulent boundary layers is already exceeded on the suction side for x/c > 0.3, at friction Reynolds numbers three times lower, while close to the trailing edge the backflow level reaches 30%. Conditional analysis of extreme events indicates that for increasing Clauser pressure-gradient parameters (reaching β ≃ 35), the flow reaches a state in which the extreme events are more likely aligned with or against the freestream, and that the otherwise strong spanwise component of the wall-shear stress reduces towards the vicinity of the trailing edge. Backflow events subjected to moderate up to strong APG conditions (0.6 < β < 4.1) exhibit an average width of Δz+ ≃ 20, and an average lifetime of Δt+ ≃ 2. This directly connects with the findings by Lenaers et al., and implies that there is a connection between high-Re ZPG and strong APG conditions.
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APA:
Vinuesa, R., Orlu, R., & Schlatter, P. (2017). Characterisation of backflow events over a wing section. Journal of Turbulence, 18(2), 170-185. https://doi.org/10.1080/14685248.2016.1259626
MLA:
Vinuesa, Ricardo, Ramis Orlu, and Philipp Schlatter. "Characterisation of backflow events over a wing section." Journal of Turbulence 18.2 (2017): 170-185.
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