 Drag-type VAWTs such as the Savonius rotor typically operate at lower tipspeed ratios than lift-based VAWTs such as Darrieus rotors and cycloturbines.The forces and the velocities acting in a Darrieus turbine are depicted in figure 1.The resultant velocity vector, formula_1, is the vectorial sum of the undisturbed upstream air velocity, formula_2, and the velocity vector of the advancing blade, formula_3.