Basic understanding of airfoil characteristics at low reynolds numbers

7th AHS Technical Meeting on VTOL Unmanned Aircraft Systems and Autonomy
  • Justin Winslow
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  • Hikaru Otsuka
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  • Bharath Govindarajan
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  • Inderjit Chopra

Copyright © 2017 by the American Helicopter Society International, Inc. A computational study has been conducted on various airfoils in simulated flows of Reynolds numbers (Re) primarily between 104 - 105 to provide understanding and guidance for MAV and other low Reynolds number designs. The computational fluid dynamics (CFD) tool utilized in this study was a Reynolds-Averaged Navier-Stokes solver with a Spalart-Allmaras turbulence model and a correlation-based laminar-turbulent boundary layer transition modeling. The airfoils investigated in this study include NACA 0009, NACA 0012 (conventional and reversed configuration), Clark-Y, flat plate airfoils (1, 3, and 5% thickness), and thin cambered plates (3, 6, and 9% camber). Airfoils were examined for lift and drag performance as well as surface pressure and flow field characteristics. In general, it is observed that below Reynolds numbers of 106, lift and drag characteristics for most airfoils cannot be assumed to be constant with Reynolds number. Below Re of 105, cambered plate airfoils are shown to have better lift and drag characteristics than thick conventional airfoils with rounded-leading edges. Flat plate performance is generally invariant to Reynolds number, but performance improves as thickness is decreased for a given Reynolds number.