Influence of Pitch, Twist, and Taper on a Blade's Performance Loss due to Roughness

The purpose of this study was to determine the influence of blade geometric parameters such as pitch, twist, and taper on a blade's sensitivity to leading edge roughness. The approach began with an evaluation of available test data of performance degradation due to roughness effects for several rotors. In addition to airfoil geometry, this evaluation suggested that a rotor's sensitivity toroughness was also influenced by the blade geometric parameters. Parametric studies were conducted using the PROP93 computer code with wind tunnel airfoil characteristics for smooth and rough surface conditions to quantify the performance loss due to roughness for tapered and twisted blades relative to a constant-chord nontwisted blade at several blade pitch angles. The results indicate that aconstant-chord nontwisted blade pitched toward stall will have the greatest losses due to roughness. The use of twist, taper, and positive blade-pitch angles all help reduce the angle-of-attack distribution along the blade for a given wind speed and the associated performance degradation due to roughness.