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Three-dimensional separation over unswept cantilevered wings at a moderate Reynolds number

Jacob M. Neal and Michael Amitay*

  • Department of Mechanical, Aerospace, and Nuclear Engineering and Rensselaer Polytechnic Institute, Troy, New York 12180, USA

  • *Corresponding author: amitam@rpi.edu
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Phys. Rev. Fluids 8, 014703 – Published 19 January, 2023

DOI: https://doi.org/10.1103/PhysRevFluids.8.014703

Abstract

An experimental investigation of separated flows over unswept, cantilevered wings with a NACA 0015 cross section is presented. For all experiments, the chord-based Reynolds number was 3.3×105. The results include qualitative surface topology from oil flow visualizations at angles of attack between 15∘ and 22∘ and semiaspect ratios 1, 2, and 4, as well as quantitative three-dimensional flowfield measurements using stereo particle image velocimetry (SPIV) at an angle of attack of 22∘ and semiaspect ratio 4. For all aspect ratios two counterrotating surface foci appeared on the wings when reversed flow was present. At the lower aspect ratios, the surface foci did not occur until higher angles of attack due to a reduction in separation extent by downwash from the tip vortex which dominates a higher percentage of the span. The volumetric mean flowfield measured with SPIV over the semiaspect ratio of 4 model and in its wake revealed the counterrotating surface foci were connected by an arch vortex. Several vortex identification methods were employed to visualize the location of the arch vortex over the suction surface. The helicity and Reynolds stress fields were shown to be highly influenced by the shape of the arch vortex. The Reynolds shear stresses containing spanwise velocity fluctuations were influenced by the tip vortex and the root horseshoe vortex, and as such had greater magnitude than the spanwise Reynolds stresses measured in a previous study of an induced stall cell on a wall-to-wall wing. In addition, time-resolved flowfield measurements showed that power spectra at the stall cell center had a dominant shedding frequency of St=0.17. At the center of the stall cell focus, the power spectra peaked at St=0.19 and St=0.21. Analysis of the instantaneous flowfield at the midspan characterized the shedding of vortices into the near wake as an intermittent phenomenon where the magnitude of velocity fluctuations associated with the shedding would increase and decrease over time at periods on the order of ten shedding cycles.

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Phys. Rev. Fluids 8, 014703– Published 19 January, 2023
  • Received 24 September 2022
  • Accepted 15 December 2022
Article part of CHORUS
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