Darrieus VAWT: Serrated Vs. Plain Airfoil

Serrated Airfoil and Plain Airfoil Comparison, Darrieus VAWT, ANSYS Fluent CFD Simulation Training

Description

This project compares airflow behavior over two H-type Darrieus wind turbines — one with plain airfoils and one with serrated airfoils — using ANSYS Fluent. The Darrieus wind turbine is a vertical axis wind turbine (VAWT) that generates electricity from wind energy using several curved airfoil blades mounted on a rotating vertical shaft. A key advantage of vertical axis turbines is that they require no adjustment to wind direction and can operate effectively at low altitudes.

The 3D geometry was built in Design Modeler, comprising a rotating zone and a surrounding stationary zone, with the computational domain measuring 50 cm in length and width and 300 cm in height. The domain was meshed in ANSYS Meshing using a hybrid approach — structured mesh in the stationary zone and unstructured mesh in the rotating zone — totaling 1,186,185 elements. Given the use of mesh motion for the rotating blades, the simulation was run using a transient solver.

Methodology

VAWT performance is substantially affected by the dynamic stall phenomenon, driven by continuous variation in blade angle of attack as the turbine rotates. Large, sudden torque fluctuations occur as dynamic stall vortices form near the blade leading edge and are carried downstream — a behavior that occurs periodically at relatively low Reynolds numbers (Re < 10⁵), producing a sharp drop in lift coefficient and reducing both rotor torque and power output.

This project investigates whether applying sinusoidal serrations to the leading edge of the turbine blades can control and reduce this dynamic flow separation, comparing the resulting performance directly against a conventional plain-airfoil H-type VAWT. Airflow entered the domain at 7 m/s, with turbulence resolved using the RNG k-epsilon model. Blade rotation was captured using Mesh Motion, with the rotating domain set to 2.8285 rad/s.

Conclusion

Results include 2D contours of pressure, velocity, and streamlines. Pressure contours show continuous variation across the blades as their position and angle of attack change throughout rotation — a core source of the dynamic stall challenge inherent to VAWT operation, and a contributor to blade fatigue given the wide range of forces experienced during each rotation cycle.

Comparing the two designs revealed a slight increase in drag on the serrated airfoils relative to the plain ones, attributable to their increased surface area. However, lift coefficient also showed a slight increase with the serrated design, resulting from a smoother pressure gradient distribution across each airfoil's two surfaces compared to the plain configuration. This smoother pressure distribution ultimately translated into a modest increase in generated power, with the serrated airfoils producing more consistent, elevated power output across each rotation cycle — confirming that leading-edge serrations offer a meaningful, if incremental, performance improvement for H-type Darrieus VAWT designs.