Savonius wind turbines, characterized by its simplicity, ability to capture wind from any direction, and efficiency in low-speed conditions, offer an attractive solution for decentralized renewable energy production, especially in urban and isolated areas. Their durable construction and simplicity of production make them an attractive alternative for conventional horizontal axis turbines. Advanced CFD simulations are crucial for comprehensive understanding and performance optimization. The incorporation of 6DOF (six degrees of freedom) dynamic mesh capabilities in software such as ANSYS Fluent facilitates an in-depth study of the turbine’s rotational mechanics and its interaction with the ambient airflow. This dynamic methodology is essential for precisely forecasting performance, identifying design enhancement opportunities, and eventually improving the efficiency and reliability of Savonius wind turbines, thus encouraging the wider use of sustainable energy technologies.

Figure 1: Schematic of Savonius Wind Turbine Using 6DOF Dynamic Mesh CFD Simulation

Simulation Process

The geometry model is initially erected using Design Modeler, established from two distinct zone. One stands for the rotational zone and the other for the surroundings. The two-blade savonius wind turbine is then meshed via ANSYS Meshing, adopting 51262 quadrilateral cells, shown in Fig. 2. It is worth mentioning that a boundary layer is created on the blades. As the title of the project suggests, this is not a simple operating condition simulation. We employed 6-DOF Dynamic mesh model to follow the savonius turbine performance from its starting point until it reaches working condition. The transient simulation regenerate the grid over time adopting Smoothing & Remeshing techniques.

Figure 2: Quadrilaterals dominate cells around two-blade Savonius wind turbine

Post-processing

The pressure contour indicates a notable pressure gradient across the turbine blades, with highest values of about 3.6 Pa on the advancing blade and minimum values of -34 Pa on the retreating blade. This significant pressure differential produces the basic torque that starts and continues the turbine’s rotation. The uneven pressure distribution is notably apparent around the S-shaped rotor design, where the concave surfaces efficiently collect and redirect the incoming flow, resulting in high-pressure zones that facilitate positive torque development. The pressure field spreads significantly beyond the rotor’s immediate area, signifying the turbine’s impact on the surrounding flow field.

Figure 3: Pressure distribution of Savonius Wind Turbine Using 6DOF Dynamic Mesh CFD Simulation – ANSYS Fluent Tutorial

The velocity contours and streamlines illustrate detailed flow phenomena, with velocities varying from 0 to 7.1 m/s. The streamline visualization illustrates clear flow patterns: an important acceleration zone around the blade tips (red-orange areas), notable flow separation on the convex surfaces, and an obvious wake structure downstream. The formation of vortices is clearly observable in the wake region, marked by the spiral patterns in the streamlines and the fluctuating velocity magnitudes. The wake structure shows a velocity reaching many rotor diameters downstream, representing the energy extraction from the flow. The existence of recirculation zones and secondary flows, especially in the inter-blade region, indicates energy losses due to viscous dissipation and turbulent mixing. The flow characteristics are characteristic of drag-type wind turbines and are essential in influencing the overall efficiency of the Savonius rotor.

Figure 4: Streamline around Savonius Wind Turbine Using 6DOF Dynamic Mesh CFD Simulation – ANSYS Fluent Tutorial