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The effect of turbulence on a flexible finite wing: forces, deflections and the wingtip vortex
Department of Energy & Process Engineering, Norwegian University of Science & Technology, NO-7491 Trondheim, Norway.ORCID iD: 0000-0003-1381-9165
Department of Energy & Process Engineering, Norwegian University of Science & Technology, NO-7491 Trondheim, Norway; Department of Aerospace and Mechanical Engineering, University of Liège, Liège 4000, Belgium.
KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics. Department of Energy & Process Engineering, Norwegian University of Science & Technology, NO-7491 Trondheim, Norway.ORCID iD: 0000-0002-3787-3118
Department of Energy & Process Engineering, Norwegian University of Science & Technology, NO-7491 Trondheim, Norway.ORCID iD: 0000-0002-9178-1070
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2025 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 1019, article id A38Article in journal (Refereed) Published
Abstract [en]

The impact of freestream turbulence (FST) on the aerodynamic performance of a flexible finite wing and the produced wingtip vortex was investigated. The wing had a NACA 4412 airfoil profile and the chord-based Reynolds number was . The experiments were conducted in a closed-loop wind tunnel with four different inflow turbulence intensities ( , , and ) generated using an active turbulence grid. Force balance measurements revealed that increasing the scale of the FST increased the maximum lift and delayed stall. Digital image correlation (DIC) measured deflections of the wing’s structure. Spanwise bending was found to be the dominant deformation. While the wing vibrated at its natural frequency in all conditions, FST increased the amplitude of the vibrations. A similar spectral signature was observed in the lift force fluctuations as well. Stereoscopic particle image velocimetry measurements were obtained two chord lengths downstream of the trailing edge simultaneously with DIC. FST decreased the vortex strength, and marginally increased vortex diffusion and size. It also increased the vortex meandering amplitude, while reducing the meandering frequency band. For the cases with a turbulence intensity of and , the frequency of meandering and the wing’s vibration were similar and a phase relation between the two motions was observed. Proper orthogonal decomposition of the vortex (after removing meandering) and the subsequent velocity field reconstruction revealed temporal fluctuations in the vortex strength at the same frequency as the wing’s vibration. This was linked to the lift force fluctuations induced by the wing’s deformations.

Place, publisher, year, edition, pages
Cambridge University Press (CUP) , 2025. Vol. 1019, article id A38
National Category
Fluid Mechanics
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URN: urn:nbn:se:kth:diva-370141DOI: 10.1017/jfm.2025.10558ISI: 001574383100001Scopus ID: 2-s2.0-105017148901OAI: oai:DiVA.org:kth-370141DiVA, id: diva2:1999688
Note

QC 20250923

Available from: 2025-09-22 Created: 2025-09-22 Last updated: 2025-10-03Bibliographically approved

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Neunaber, Ingrid

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