Serrated Vs. Plain Airfoil: Darrieus VAWT

Description

This project compares the airflow over two H-type Darrieus vertical axis wind turbines (VAWTs) — one with plain airfoil blades and one with serrated leading-edge blades — using ANSYS Fluent. A Darrieus turbine generates electricity from wind using several curved airfoil blades on a vertical rotating shaft; because the rotor is vertical, it needs no adjustment to wind direction and works well at low altitudes. The study investigates whether sinusoidal serrations on the blade leading edge can control the dynamic stall that limits VAWT performance, improving power and torque.

Methodology

The three-dimensional geometry is produced in Design Modeler, containing a rotating zone and a stationary zone, with a calculation area 50 cm in length and width and 300 cm in height. Meshing is performed in ANSYS Meshing with a hybrid mesh — structured for the stationary zone and unstructured for the rotating zone — giving an element count of 1,186,185. The transient solver is enabled, with the Mesh Motion option used to simulate the rotating motion of the blades. The performance of VAWTs is strongly affected by the dynamic stall induced by the continuous variation in the blades' angle of attack as they rotate: at relatively low Reynolds number, dynamic stall vortices form near the leading edge and shed downstream, causing large, sudden torque fluctuations and a sharp drop in lift that reduces rotor torque and power. To address this, the project compares plain blades against blades with sinusoidal leading-edge serrations designed to control the dynamic flow separation. The airflow enters the domain at 7 m/s, the RNG k-epsilon model solves the turbulent flow, and the rotating domain turns at 2.8285 rad/s.

Analysis

After the solution, 2D contours of pressure, velocity, and streamlines are obtained. The pressure contours show that the load on the blades changes constantly as their position and angle of attack vary through each rotation — the source of the dynamic stall and of the fatigue-inducing force variation that challenge VAWTs. Comparing the drag, lift, and power coefficients of the two designs shows that the serrated airfoils produce a slight increase in drag (from their larger surface area), a slight increase in lift (from a smoother pressure distribution across the blade surfaces), and, overall, a modest increase in generated power, with a smoother power output through each rotation cycle. By the end of this project, you'll be able to set up a transient Mesh Motion simulation of a vertical-axis wind turbine, run a comparative study of plain versus serrated leading-edge blades, and interpret the pressure, lift, drag, and power-coefficient results that reveal how blade design mitigates dynamic stall and improves VAWT performance.