The aerodynamic behavior of vertical-axis wind turbines (VAWTs), particularly the H-type Darrieus
configuration, remains central to renewable energy research due to persistent challenges in self-starting and efficiency
at low tip speed ratios (TSRs). This study presents a numerical investigation of a modified NACA0018 aerofoil with
chordwise surface openings, termed a J-shaped aerofoil, operating under Darrieus motion. Two-dimensional CFD
simulations in ANSYS Fluent evaluated opening ratios of 30%, 60%, and 90% of chord length, focusing on lift, drag,
and chordwise force coefficients during dynamic stall. A validated oscillating aerofoil model with user-defined
pitching replicated Darrieus kinematics, with systematic variation of TSR and pitch angle. Results show that larger
openings enhance lift and delay stall onset in the positive angle of attack phase, improving self-starting potential.
However, these gains are offset by increased drag and reduced performance during the negative phase, particularly
downstream. The J-shaped aerofoil with 90% opening achieved ~30% higher peak lift than the conventional profile,
with improved flow reattachment and vortex dynamics observed. Despite elevated downstream losses, the enhanced
upstream torque indicates a net advantage for turbine start-up capability. These findings provide insight for
optimizing blade design in low-Reynolds-number VAWTs, balancing self-starting improvement against efficiency at
higher TSRs.
Yunus Celik — 1)Energy2050, Department of Mechanical Engineering, Faculty of Engineering, University of Sheffield, Western Bank S10 2TN, Sheffield, United Kingdom 2)Department of Aeronautical Engineering, Sivas University of Science and Technology, Gültepe Mahallesi 58000, Sivas, Turkey
Derek Ingham — Energy2050, Department of Mechanical Engineering, Faculty of Engineering, University of Sheffield, Western Bank S10 2TN, Sheffield, United Kingdom
Lin Ma — Energy2050, Department of Mechanical Engineering, Faculty of Engineering, University of Sheffield, Western Bank S10 2TN, Sheffield, United Kingdom
Burhan Necati Kiziloglu — Department of Aeronautical Engineering, Sivas University of Science and Technology, Gültepe Mahallesi 58000, Sivas, Turkey
Mohamed Pourkashanian — Energy2050, Department of Mechanical Engineering, Faculty of Engineering, University of Sheffield, Western Bank S10 2TN, Sheffield, United Kingdom
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