Abstract: Reynolds number of high altitude long endurance （HALE） UAV in cruise state is small, thus the viscous effects on boundary layer and aerodynamic performance are serious. In this paper, the effects of Reynolds number on the boundary layer and aerodynamic characteristics of a supercritical laminar wing are presented. The laminar-transition-turbulent characteristics of three-dimensional boundary layers of the wing are investigated by using a numerical method. The effects of Reynolds number on boundary layer characteristics, and specially on the transition location and skin friction drag, are compared under high altitude lower Reynolds number and middle altitude high Reynolds number situations to analyze the effects in detail. The investigation shows that Reynolds number seriously affects the thickness of boundary layer, the skin friction drag and the ratio of lift to drag of HALE UAV, but has only a little effect on the boundary layer transition and lift coefficient. Thus the laminar wing technology can be used in HALE UAV design.

Key words: Reynolds number effect, supercritical, laminar wing, 3D boundary layer, transition