A comparative study review: The performance of Savonius-type rotors

The utilization of renewable energy harvesting equipment is one of the methods to reduce the level of environmental pollution risks to the world. Water and wind are considered as environmental potential resources which have become attractive features of urban utilization through different wind and hydrokinetic turbine design technology. While no large-scale Savonius turbines have been developed yet, one of the popular designs is the small-scale rotor, which utilizes a drag-based vertical axis. The advantages of this type of rotor are easy to design, inexpensive, perform well at low speed, and have the capacity to turn independently to the wind-water direction flow. However, through a number of investigations on the performance the Savonius rotor, it was found to suffer from inefficient operation and a large amount of negative torques produced by the returning blade. To resolve the limitations in performance of the Savonius turbine, many optimization techniques and assessments have been conducted on different rotor types. The studies presented and discussed the challenges and changes in variations of rotor design parameters and their significant influence on rotor performance. In order to increase the unit's output without extra cost, improving variable parameters and reducing torques were accomplished in the negative direction while decreasing maintenance cost. Hence, the data collected were classified based on geometric and installation aspect parameters, and different optimization studies were summarized based on several influencing parameters.