Darrieus-type Vertical Axis Wind Turbines (VAWT) are promising for small scale decentralized power generation because of their unique advantages such as simple design, insensitive to wind direction, reliability, and ease of maintenance. Despite these positive aspects, poor self-starting capability and low efficiency in weak and unsteady winds deteriorate further development. Adaptive Hybrid Darrieus Turbine (AHDT) was proposed by the author in the past study as a potential solution to enhance low wind speed characteristics. The objective of the current research is to optimize the parameters of AHDT. AHDT integrates a dynamically varying Savonius rotor with a Darrieus rotor. A fully detailed 2D numerical study employing Reynold-Averaged Navier Stokes (RANS) is carried out to investigate the impact of the Darrieus rotor diameter (DR) on the Savonius rotor (DT) with regard to hybrid turbine performance. The power coefficient of the Darrieus rotor is evaluated when the Savonius rotor is in the closed condition (cylinder) of various diameters. The influence of Reynolds number (Re) on the torque coefficient is examined. Power loss of 58.3% and 25% is reported for DR/DT ratio of 1.5 and 2 respectively for AHDT with solidity 0.5 at 9 m/s. The flow interaction between the Savonius rotor in closed configuration reveals the formation of von Karman vortices that interact with Darrieus blades resulting in flow detachment. An optimum diametrical ratio (DR/DT) of 3 is found to yield the maximum power coefficient of the Darrieus rotor.

Computational Optimization of Adaptive Hybrid Darrieus Turbine: Part 1

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/we.2788

Estimation of power performances and flow characteristics for a Savonius rotor by vortex particle method

For the purpose of harvesting wind energy from low wind velocity regions such as north-east India, the Savonius-type drag-based vertical-axis wind turbine (VAWT) can be a potential candidate due to direction independency, absence of yaw mechanism, small-scale stand-alone systems and ease of fabrication due to absence of airfoil-shaped blades. Based on the aforementioned merits, it is decided to conduct a performance improvement task by developing a novel blade shape bio-inspired from the polyp leaf of the orange sea-pen (Ptilosarcus gurneyi). The similarities between flow physics of the Savonius rotor and the feeding mechanism of the sea-pen are discussed. The procedure of shape extraction for novel blade is narrated and the rotors are fabricated. Wind tunnel experimentation and 2D numerical simulations are performed for preliminary performance assessment of the rotors. The performance potential of the novel blades is assessed in comparison with the semicircular blade. The result indicated the possibility of the performance improvement in case of novel bio-inspired blade. 

Development of a Novel Drag-Based Vertical-Axis Wind Rotor Inspired from Orange Sea-Pen

\n Over the last few decades, the vertical-axis wind turbines (VAWTs) have undergone intensive research mainly due to their design simplicity and independency of wind direction. The drag-based Savonius wind rotor exhibits a better starting capability, whereas the lift-based Darrieus wind rotor achieves higher efficiency over a wider operating range. Thus, in order to capitalize on their advantages, both the rotors are mounted on the same axis to form a hybrid/combined system. In this review paper, an attempt has been made to collect and analyze the past research studies in the field of hybrid wind rotors. An optimization route has also been suggested for the design of such a hybrid wind rotor to ensure that the design complexity is minimized, and at the same time, both the Savonius and the Darrieus rotors are utilized to their fullest potential. In this regard, a few important parameters are identified whose effects on the hybrid rotor performance must be investigated in future studies. Suggestions and direction of research are presented keeping in mind the improvement of the technology.

Jyotirmoy Sarma

Papers

Hybrid/Combined Darrieus–Savonius Wind Turbines: Erstwhile Development and Future Prognosis