Robust optimization of Savonius-type wind turbine deflector blades considering wind direction sensitivity and production material decrease

Savonius-type vertical axis wind turbine (SWT) has several characteristics appropriate for urban usage: low rotational speed, low noise, easy self-starting; but also has a low power coefficient. One of the methods to improve the SWT efficiency is to use fixed deflector blades, but this makes the SWT performance sensitive to wind direction. This paper performs a robust optimization of deflector blade shape, considering the whole range of wind directions. The objectives are to reduce the required production material and to maximize the annual energy production (which is related to the average power coefficient cPave). Each design efficiency is estimated using 2D CFD transient simulation with GEKO turbulence model. The results show that cPave is increased to cPave = 0.35 using an 8-blade optimized deflector (46% improvement compared to no-deflector) coupled with classical SWT rotor. The 4-blade deflector is inferior with 33% improvement (cPave = 0.32) but with 60% material reduction compared to the previous design. Application of the novel Scooplet-based design achieves a further improvement of cPave = 0.43 and cP,ave = 0.385 for 4-blade and 8-blade deflectors, respectively. A selected optimized design was evaluated using 3D CFD for various aspect ratios (Ar).