Surface roughness plays a critical role in the aerodynamic performance of airfoils, horizontal-axis wind turbines (HAWTs), and vertical-axis wind turbines (VAWTs) across low Reynolds number (Re 100 000), moderate (Re ≈ 100 000–1 000 000), and high Re (Re 1 000 000). For airfoils, leading-edge roughness (LER) and distributed surface imperfections influence lift (CL), drag (CD), and lift-to-drag ratio (L/D) coefficients by affecting boundary layer transition, stall onset, and aerodynamic efficiency. Passive devices such as vortex generators (VGs), dimples, and grooves mitigate adverse effects, particularly at high Re, by delaying stall and enhancing L/D. HAWT blades exhibit similar roughness-induced effects; however, three-dimensional flow, rotational dynamics, and spanwise variations introduce distinct responses. Blade-scale roughness combined with passive devices significantly affects stall behavior, power coefficient (Cp), and efficiency at low tip-speed ratios (TSRs), emphasizing the role of operating Re and angle of attack (AoA). For VAWTs, roughness effects have mainly been studied at low-to-moderate Re (Re 300 000). Artificial roughness, zigzag tapes (ZTs), and groove-flap modifications influence torque, Cp, and stall over wide AoA ranges, while high-Re data remain scarce, revealing a critical knowledge gap for urban and low-speed wind turbine applications. Across all configurations, roughness height, type, and location govern laminar-to-turbulent transition and separation control, while differences arise from operating regimes, rotational effects, and blade geometry. This comparative analysis provides a unified framework and design guidelines to optimize aerodynamic performance and energy extraction under varied Re conditions.
Davari et al. (Sun,) studied this question.