This study investigates the impact of zigzag tape on the aerodynamic performance and wake characteristics of the Delft Vertical Axis Wind Turbine (VAWT). The primary aim is to understand how the zigzag tape affects blade loads and the resulting aerodynamic wake. A comprehensive analysis was conducted using the Actuator Line Model (ALM) with airfoil characteristics measured in the wind tunnel at the Technical University of Denmark (DTU). Additionally, a 2-D CFD analysis with k-ω SST and γ-Re_θ turbulence models were employed to evaluate the influence of laminar transition phenomena on rotor characteristics. Results indicate that while the zigzag tape linearizes the lift coefficient characteristic, it leads to a notable reduction in aerodynamic efficiency due to increased drag and decreased lift below the critical angle of attack. The simulations were performed at a tip-speed ratio (TSR) of 4.5 to avoid a dynamic stall, as this operating condition ensures that the rotor blades remain below the static stall threshold and large offshore VAWTs are designed to operate near their maximum aerodynamic efficiency (C_P) for the majority of their operational time. The aerodynamic wake behind the rotor also shows significant changes, with the zigzag tape promoting asymmetry and affecting the wake recovery distance. The study's findings highlight the importance of considering surface contamination effects, represented by zigzag tape, in evaluating VAWT performance and wake behavior, offering valuable insights for wind turbine design and optimization.

This work concerns high-fidelity numerical simulations of a rotor wake, with focus on the tip vortices and their stability. Blade-resolved and actuator line lattice-Boltzmann simulations are performed on a symmetric baseline rotor, as well as on a rotor with asymmetries. The asymmetry has the purpose of destabilizing the tip vortices to enhance wake recovery and hence the performance of potential downstream turbines. Limitations in the actuator line method are highlighted, and we show the potential of addressing these limitations with a so-called “preset” actuator line, where the forces are extracted from blade-resolved simulations, or an analytical load model, which as input only requires the thrust and power coefficients. Simulations agree well with experimental results and leapfrogging is captured, even with a coarse actuator line simulation. The asymmetric rotor is shown to improve power in the far-wake by 12%.