Effects of axisymmetric-omnidirectional deflector on aerodynamics of modified Bach Savonius rotor for power enhancement

• Published in: Energy conversion and management 2023-12, Vol.297, p.117720, Article 117720
• Main Authors: Tomar, Shivam Singh, Dewan, Anupam, Singh, Tej Pratap
• Format: Article
• Language: English
• Subjects: administrative management; aerodynamics; Axisymmetric omnidirectional deflector; Bach rotor; energy conversion; mountains; Overlap ratio; Power coefficient; Savonius rotor; torque; Torque coefficient; wind
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2023.117720

•Axisymmetric omnidirectional deflector for Bach rotor used.•Varying overlap ratio on high shape factor for Bach rotor considered.•Optimum overlap ratio for high shape factor designs obtained.•Fluid flow characteristics are explored.•8.78% increment in power coefficient for Bach rotor observed. A Savonius turbine can be highly effective for mountainous terrains and hydro channel applications with low flow speeds, owing to its low cut-in speeds, ease of maintenance, and self-starting nature. However, a challenge arises due to its low power output because of adverse torque produced by the returning blade. The present computational study aims to address this issue by considering a modified Bach rotor design with a varying overlap ratio at a high shape factor. Additionally, the axisymmetric omnidirectional deflector (AOD) for the Bach rotor is also studied. The tip speed ratio varies from 0.4 to 1.3. The results indicate that the maximum power coefficient of 0.249 is achieved for the Bach-AOD rotor at a tip speed ratio of 1.0. The overlap ratio of 0.2 shows negative gauge pressure in the overlap region, leading to the suction of flow onto the concave part of the returning blade. The AOD configuration enhances the positive gauge pressure area on the concave side of the advancing blade. By comparing conventional semicircular rotors with the present Bach-AOD rotor, a maximum increase of 42.68% in power coefficient at a tip speed ratio of 0.4 is observed. Both the Bach-AOD configuration and Bach rotor with an overlap ratio of 0.25 achieve a relatively constant power coefficient at a tip speed ratio larger than 0.6. The findings of the present study lead to a rotor design that maintains the same efficiency at variable wind speeds as long as it operates at the same rotational speeds.