No abstract

Savonius drag-type wind turbine suffers from poor efficiency due to adverse negative torques on returning blades when they rotate against incoming flows. It was proven that using a suitable deflector system has potential to improve wind turbine efficiency. However, as previously identified in studies, the common drawback of using flat deflector is strong wake zone behind it. Present study aims to improve overall performance of drag-type wind turbine by using a cylinder deflector with wake splitter plate to manage and mitigate detrimental effect of wake zone behind deflector. Wake control and suppressing vortex shedding downstream of circular cylinder have been divided into active and passive flow control techniques. Amid latter control methods, adoption of splitter plates has proven to be highly effective for wake control and suppressing vortex shedding behind cylinder. Unlike previous studies, a cylinder deflector with the wake splitter plate will be utilized instead of conventional deflectors to improve efficiency of wind turbine by disturbing wake zone downstream of deflector. To obtain more efficient configuration, effect of variations of wake splitter length (Ls/D), attachment angle (θwsp), and count of wake splitters on outputs such as generated torque coefficient, power coefficient and wake zone on performance of Savonius rotor were investigated via Computational Fluid Dynamics simulation. The results revealed that cylinder deflector with wake splitter increased Savonius rotor's performance most for almost all Tip Speed Ratios. The average Cm and CP raised considerably up to 15% using deflector with two wake splitters at TSR=0.6 compared to case without deflectors.

To achieve high fuel efficiency, vehicles designs are inclined to choose lightweight materials and structures. However, these structures are generally weak, and structural integrity is a common concern. The purpose of this paper is to carry out fluid-structure interaction (FSI) study in one-way coupling analysis on a Shell Eco Marathon (SEM) prototype car which travels in a low-speed range to analyse its structural response. A new set of economical materials is proposed and analysed with the concern on self-fabrication process. The Flax fibre composite is introduced as a part of the proposed material set due to its environmental and economic advantages. The study herein is purely a numerical simulation work as a first approach to design a sustainable SEM prototype car. The fully assembled SEM prototype car was analysed with the proposed materials with ANSYS Workbench in the coupling of the fluid (ANSYS Fluent) and structural solver (ANSYS Mechanical) in a one-way FSI. Even with a thin shell design, the proposed material only experiences minimum deformations. The simulations also reveal that the maximum von-Mises stress experienced, after considered the safety factor, is still several order lower than the yield strength. This study has confirmed that the car design has fulfilled its structural requirements to operate at the design speed.

The Savonius wind turbine is a vertical-axis wind turbine invented in 1930s consisting of a cylindrical drum with semi-circular blades attached to the drum. It is popular for its simple design, low costs, and self-starting ability, making it feasible for rural areas. As a rotating device, the blade is considered an important component of the Savonius turbine because it captures energy from omni-directional wind flow and converts it into mechanical/electrical energy. Blade corrosion can cause a surface degradation which affects blade's aerodynamic and structural performance. The relation between surface roughness and turbine performance has been addressed in various studies, however, most of these studies focussed on horizontal-axis wind turbine (HAWT). This study analysed the performance of a static Savonius turbine using three-dimensional (3D) computer simulation at different blade angle positions through one-way fluid-structure-interaction (FSI) in terms of static coefficients, von Mises stresses and deformation with different surface roughness at different wind velocity. The simulation reveals that the position with highest static torque coefficient is when the turbine is resting at 15o with respect to the flow direction. The flow velocity increases the performance however, surface roughness deteriorates the flow and decreases the static coefficient. The simulation herein predicts no structural failure and different materials exhibit different maximum stress and deformation showing the importance of material selection in turbine blade development. The findings from this study helps finding a suitable material for the development of Savonius turbine from a material point of view to minimize turbine downtime and potentially save cost

The drag-driven vertical-axis turbines with semicircular rotor blades, commonly known as Savonius turbines, remain potentially beneficial to extract renewable energy from wind and water streams, especially in terms of their practicality to provide low-cost solutions to rural areas. However, they suffer drawbacks due to the negative torques on their returning blades. We propose a novel solution by dynamically venting out these returning blades using controllable flaps, which retained its omnidirectional capability. Results from unsteady numerical simulations showed that the vented rotor attained a maximum average power coefficient ( CP) of 0.275 at the tip-speed ratio (TSR, symbolized as λ) of 0.9, which was 21.7% better than that on the unvented rotor. Furthermore, the proposed dynamically-vented blades produced large improvements in the average torque coefficient ( CT), with maximum gains of 38.3% on the returning blade at ᵰ6; = 0.4 and 24.8% on the full rotor at ᵰ6; = 1.0, relative to those on the unvented rotor. The controlled dynamic venting was beneficial because it modified the pressure distributions surrounding the returning blade, and changed the flow structure downstream of the vented blade that improved the torque on the subsequent blade entering the returning side. Elucidation on the flow dynamics revealed that the flows were vented outward through the flap aperture onto the convex side of the returning blade, rather than inward into its concave side, as initially hypothesized.