Effects of Dimples as Vortex Cavities on the Aerodynamic Performance of Darrieus

This paper investigates the aerodynamic performance enhancement of a Straight-Bladed Vertical Axis Wind Turbine (VAWT) through dimple optimization. This study employs Orthogonal Experimental Design (OED), a classical Design of Experiments (DoE) methodology, to systematically analyze dimple parameters. Initially, three key single-dimple parameters (diameter, position, depth) were investigated, followed by an extended Dual-dimple configuration incorporating six parameters (x/c, d1, l1, d2, l2, s). The OED approach achieves optimization of these multi-factor, multi-level systems with minimal computational cost by scientifically selecting representative combinations from full factorial experiments. Numerical simulations using the Transition SST turbulence model demonstrated that the optimal Dual-dimple design improved the pressure coefficient (Cpe) by 114.9% and the Cp of the optimal Dual-dimple airfoil is 0.1227 for the numerical simulation at a Tip Speed Ratio (TSR) of 3. The position x/c of dimple 1, with an Fvalue of 2.729, was identified as the most influential parameter, exceeding the significance threshold of 2.25. The design effectively delayed dynamic stall and suppressed boundary layer separation, though performance gains diminished with additional dimples or higher TSR values. These findings provide valuable insights for optimizing VAWT blade design through surface modifications.