Basic Understanding of Airfoil Characteristics at Low Reynolds Numbers (104-105)

A computational study has been conducted on various airfoils to simulate flows at Reynolds numbers (Re) primarily between 10(4) and 10(5) to provide understanding and guidance for MAV and other low-Reynolds-number designs. The computational fluid dynamics tool used in this study is a Reynolds-averaged Navier-Stokes solver with a Spalart-Allmaras turbulence model and a correlation-based laminar-turbulent boundary-layer transition model. 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 the Reynolds number of 10(6), lift and drag characteristics for most airfoils cannot be assumed to be constant with the Reynolds number. Below the Reynolds number of 10(5), 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 the Reynolds number, but performance improves as thickness is decreased for a given Reynolds number.