Numerical Study of a Novel Concept for Manufacturing Savonius Turbines with Twisted Blades

This work presents a numerical study of the aerodynamic performance and the resulting flow field of two novel Savonius wind turbines with twisted blades. The novelty relies on the blade manufacturing process which is characterized by a 'twisted cut' through the central axis of a hollow cylinder (tube), followed by a partial twisted cut in the range of 90 degrees. This approach does not require any expensive fabrication process such as blade molding and/or 3D prints, and, therefore, it can potentially mitigate the production costs. The main goal is to investigate the operational parameters and the overall performance of the presented devices, which are currently being operated in atmospheric conditions. For this purpose, three-dimensional simulations have been performed using the open-source CFD library OpenFOAM in order to solve the governing equations and for characterizing the main phenomena involved in the flow pattern. The Reynolds-averaged Navier-Stokes (RANS) approach together with the k-omega SST model were employed to reproduce the flow turbulence effects. This model is validated using wind tunnel measurements of the power (CP) and torque (CM) coefficients from a straight blade Savonius turbine. Unsteady simulations of the two turbine prototypes were investigated at different tip speed ratio TSR (lambda) by varying the rotational speed of the rotor while keeping constant the free stream (rated) velocity V infinity. The results were compared against the Savonius turbine employed for validating the model. Aerodynamic loads and general wake structure were studied at the optimal operational conditions as well. For the same turbine configurations, the new blade geometry improved the performance by 20-25% (at its optimal TSR), compared to the conventional straight blade Savonius rotor, as well as the reducing torque fluctuation