Savonius

Savonius is a type of vertical-axis wind turbine (VAWT) that uses drag forces on curved, scoop-shaped blades to generate rotation. The classic design consists of two or more semi-cylindrical blades mounted on a common vertical shaft, usually arranged in opposite phases so that each blade presents a concave surface to the wind on one side and a convex surface on the other. The simplest implementation uses two blades formed from semi-cylinders; more blades or overlapping sections can improve starting torque and torque ripple.

Operation relies on differential drag: as wind flows around the rotor, the concave faces experience higher drag than the convex faces, producing a net turning force. The vertical shaft enables independent operation from wind direction, making the rotor robust in variable winds. Savonius rotors are known for mechanical simplicity, low manufacturing costs, and ability to operate in dusty or wet environments with minimal maintenance. However, their aerodynamic efficiency is relatively low compared with modern horizontal-axis turbines; the typical performance coefficient is well below those of high-efficiency designs, though optimizations such as blade overlapping can modestly improve starting and torque.

History and use: The Savonius rotor was developed by Finnish engineer Sigurd Savonius in the early 20th century, with a patent and practical experiments dating from around 1922. It has seen use in small-scale applications such as irrigation pumping, battery charging, and other remote power needs where simplicity and reliability are prioritized over high efficiency. In contemporary practice, Savonius rotors are often employed for low-power, simple installations or as educational demonstrations, and may be used in conjunction with other turbine types to balance torque characteristics.