Effect of blade shape on aerodynamic and aeroacoustic characteristics of vertical axis wind turbines using mid-fidelity and high-fidelity methods

This research paper investigates the effect of different blade shapes on the aerodynamic and aeroacoustic characteristics of Darrieus Vertical Axis Wind Turbines (VAWTs). Three different VAWT blade shapes are investigated: Straight, Troposkein, and Helical, considering a chord-based Reynolds number of 1.73e+5 and at a constant tip speed ratio for all. The mid-fidelity Lifting Line Free Vortex Wake (LLFVW) method and the high-fidelity Lattice Boltzmann/Very Large Eddy Simulation (LB-VLES) method are employed. Power performance analysis reveals that the straight-bladed VAWT generates the highest power output (about 11% higher), followed by the helical and troposkein blade configurations. The helical-bladed rotor exhibits smoother thrust and torque distribution over a wider azimuthal angle range, as predicted by both methods. While both methods capture the same trends in thrust and torque values, the mid-fidelity LLFVW method predicts approximately 22% higher thrust and torque values and lower near-wake streamwise velocities as compared to the high-fidelity LBM. The LLFVW is unable to accurately capture the inherent 3D vortices in the VAWT flow-field and the effect of blade-vortex interaction (BVI) on the VAWT force-field, as compared to LBM. In terms of aeroacoustics, the troposkein VAWT produces the highest noise at lower frequencies (20-30 Hz), followed by the straight and helical VAWTs. However, the troposkein and helical VAWTs emit more noise at higher frequencies (500-2000 Hz) than the straight VAWT due to the higher intensity of BVI observed for the former.