Experimental Investigations on the Performance Degradation of a Low-Reynolds-Number Airfoil with Distributed Leading Edge Roughness

Modern wind turbines usually suffer unexpected power losses after long operating periods due to the contaminations accumulated at the leading edge of blades. In order to investigate the underlying physics, experiments were conducted to study the performance degradation of low-Reynolds-number airfoils induced by distributed leading edge roughness. Roughness was simulated by precisely manufactured plastic strips with different roughness height and distribution patterns. Both force and PIV measurements were performed under selected experimental conditions. Considerable reductions of lift coefficients were found for all roughness cases. While small roughness tends to delay the stalling angle, large roughness significantly advanced the aerodynamic stall. Hysteresis effects were also eliminated by applying roughness to the leading edge. Detailed PIV results revealed that small roughness tends to stabilize the boundary layer flow and delay the airfoil stall, whereas large roughness could cause earlier airfoil stall at a smaller angle of attack. In addition, comparing to distribution patterns, the roughness height was found to be a more essential factor for roughness induced performance degradation.