Computational fluid dynamical analysis of a Savonius vertical axis wind rotor array

Savonius vertical axis wind turbine (VAWT) arrays are being studied for urban and semi-urban wind energy harvesting. With limited ground space in these areas, optimizing energy extraction through various array configurations is crucial. This study presents a computational fluid dynamics (CFD) analysis of a four-rotor Savonius VAWT array. Various unit array configurations, based on wake analysis of an isolated Savonius rotors, are evaluated through detailed CFD study. The parameters of interest in this study are the coefficient of power, C-pi ( i= 1, 2, 3, or 4 is the rotor number) at different typical values of the tip-speed ratio, lambda=Omega D/2U(infinity) (where Omega is the angular speed of the rotor, D is the diameter of the rotor, and U-infinity is the free stream air velocity) of the constituent rotors of the unit array, rotational orientation as well as the average value of the coefficient of power, C-pa=(& sum;C-4(i=1)pi)/4. It is observed that at certain configurations of the four-unit array, it is possible to have a power enhancement, Psi=C-pa/C-p0>1 up to 1.34 (34% gain), where C-p0 is the coefficient of power of an isolated Savonius rotor at the same lambda. The observed enhancement is explained using velocity and pressure fields around the unit array. Comparative analysis with previous studies highlights new approaches for designing high-performance Savonius arrays and suggests directions for CFD-based optimization of larger arrays.