Savonius VAWT

Savonius VAWT CFD Simulation with Mesh Motion in ANSYS Fluent

Description

This study investigates the airflow behavior and aerodynamic performance of a Savonius vertical axis wind turbine (VAWT) using ANSYS Fluent, evaluating pressure and velocity distribution around the rotor blades and analyzing the flow patterns developing during turbine operation. The simulation runs under transient conditions to capture the dynamic behavior of the rotating blades, along with the unsteady flow separation and vortex formation characteristic of Savonius rotors. The computational domain includes both a rotating rotor region and a stationary surrounding flow domain to accurately capture the interaction with incoming airflow.

The geometry, representing a three-bladed Savonius VAWT rotor enclosed within a domain providing sufficient clearance for airflow, was designed in Design Modeler. Meshing was performed in ANSYS Meshing using a non-conformal, unstructured mesh to accommodate the complex blade geometry and accurately resolve boundary layer effects, totaling approximately 5.5 million cells, with refinement concentrated near the rotor surfaces to better capture velocity gradients and flow separation.

Methodology

The simulation used a pressure-based transient solver suited to incompressible flow, with air modeled as a Newtonian, incompressible fluid. Turbulence was resolved using the RNG k-epsilon model, selected for its strong performance in swirling and recirculating flows — behavior common to Savonius VAWT operation.

The domain was divided into two zones: a rotating rotor zone and a stationary flow zone, with mesh motion applied to the rotor zone at a rotational speed of 144 rpm to represent turbine rotation. Boundary conditions included a velocity inlet at 12 m/s, a pressure outlet downstream, and no-slip walls on the turbine surfaces. The SIMPLE algorithm handled pressure-velocity coupling, with second-order discretization applied to both momentum and turbulence equations for improved accuracy.

Conclusion

Pressure contours reveal high-pressure regions on the windward side of the blades and low-pressure regions on the leeward side, confirming that torque generation arises from this differential pressure force across the rotor. Velocity contours and streamlines reveal complex vortex structures and recirculation zones forming behind the rotor, illustrating the unsteady wake dynamics characteristic of drag-based turbines like the Savonius design.

Velocity vectors further show how airflow deflects and accelerates around the blades, while the streamlines visualize the rotational flow entrainment occurring near the rotor arms. The overall flow pattern indicates a consistent power extraction process, though localized flow separation and elevated turbulence intensity in certain regions may reduce overall efficiency — together validating the Savonius VAWT's expected aerodynamic behavior and confirming CFD's effectiveness as a tool for evaluating this turbine design's performance.