Effect of fences on airfoil aerodynamics at -90 degree incidence

Abstract

A two-dimensional computational method is applied to accurately calculate the viscous flow about airfoils normal to the freestream flow. In particular, the flow about an XV-15 wing airfoil with an upper or lower surface fence at -90 deg incidence is evaluated. A parametric study is conducted to investigate and understand the effect of fences on the flow about an airfoil normal to the freestream flow. This investigation includes the effect of fence location for both upper and lower surfaces and of fence height on airfoil aerodynamic characteristics. Comparisons of the time-averaged lift, drag, pitching moment, and surface pressure distributions are made to evaluate the effectiveness of each airfoil/fence configuration. The results indicate that 1) the airfoil drag is highly dependent on the fence chordwise location, ranging from a 15% increase in drag for an upper surface fence to a 35% decrease in drag for a lower surface fence with respect to the basic airfoil value ; 2) the airfoil drag is also dependent on the fence height, with a drag reduction of 25% for a lower surface fence of 35% chord height located at 15% chord ; and 3) the reduction in drag is the direct result of decreased pressure on the airfoil upper surface near the leading edge and an increase in the lower surface pressure over the entire airfoil chord.