Numerical and experimental study of a helical Savonius wind turbine and a comparison with a two-stage Savonius turbine

In this paper, the aerodynamic performance of a helical Savonius rotor model with 180 degrees twisted blades is investigated numerically and experimentally. It is also performed a comparison of results with a two-stage Savonius with similar parameters. The experimental study is conducted in the aerodynamic tunnel Prof. Debi Pada Sadhu at the Fluid Mechanics Laboratory of UFRGS. Numerical simulations are performed using the Finite Volumes Method performed by the solution of the Reynolds Averaged Navier-Stokes (RANS) using the k-omega SST turbulence model. The static torque, dynamic torque and power coefficients are compared. Results show that the turbine has a positive static torque coefficient for any studied rotor angles. The dynamic torque coefficient of the turbine shows less torque variation along each rotation in comparison with a two-stage turbine, reaching the maximum value for a tip speed ratio (lambda) of 0.2 for the experimental and numerical cases. The helical turbine, despite having a more complex manufacturing process than the two-stage turbine, presents stable torque and higher power coefficient. The maximum power coefficient of the rotor is obtained for lambda of 0.65 for both cases. The numerical simulations and the experimental results present differences between 2.34% and 12.5% in C-T and C-P values. (C) 2019 Elsevier Ltd. All rights reserved.