To analyze the complex and unsteady aerodynamic flow associated with wind turbine functioning, computational fluid dynamics (CFD) is an attractive and powerful method. In this work, the influence of different numerical aspects on the accuracy of simulating a rotating wind turbine is studied. In particular, the effects of mesh size and structure, time step and rotational velocity have been taken into account for simulation of different wind turbine geometries. The applicative goal of this study is the comparison of the performance between a straight blade vertical axis wind turbine and a helical blade one. Analyses are carried out through the use of computational fluid dynamic ANSYS® Fluent® software, solving the Reynolds averaged Navier–Stokes (RANS) equations. At first, two-dimensional simulations are used in a preliminary setup of the numerical procedure and to compute approximated performance parameters, namely the torque, power, lift and drag coefficients. Then, three-dimensional simulations are carried out with the aim of an accurate determination of the differences in the complex aerodynamic flow associated with the straight and the helical blade turbines. Static and dynamic results are then reported for different values of rotational speed.

3D CFD Analysis of a Vertical Axis Wind Turbine

Under the inspiration of polar coordinates, a novel parametric modeling and optimization method for Savonius wind turbines was proposed to obtain the highest power output, in which a quadratic polynomial curve was bent to describe a blade. Only two design parameters are needed for the shape-complicated blade. Therefore, this novel method reduces sampling scale. A series of transient simulations was run to get the optimal performance coefficient (power coefficient C p) for different modified turbines based on computational fluid dynamics (CFD) method. Then, a global response surface model and a more precise local response surface model were created according to Kriging Method. These models defined the relationship between optimization objective Cp and design parameters. Particle swarm optimization (PSO) algorithm was applied to find the optimal design based on these response surface models. Finally, the optimal Savonius blade shaped like a “hook” was obtained. Cm (torque coefficient), Cp and flow structure were compared for the optimal design and the classical design. The results demonstrate that the optimal Savonius turbine has excellent comprehensive performance. The power coefficient Cp is significantly increased from 0.247 to 0.262 (6% higher). The weight of the optimal blade is reduced by 17.9%.

A Novel Parametric Modeling Method and Optimal Design for Savonius Wind Turbines

The blade profiles and blade shapes of vertical-axis Savonius wind turbine rotors have undergone a series of changes over the past three decades. Wind turbine aerodynamicists have carried out numerous computational and experimental research to arrive at a suitable rotor blade design configuration so as to harvest maximum energy from the available wind. In most of the studies, the geometric and aerodynamic aspects of the rotor blade design have been reported. Interestingly enough, a couple of review papers got published in the area of Savonius rotors during the last one decade. However, there is not a single piece of literature that gives a comprehensive and a systematic review of Savonius rotor blade profiles and shapes. This paper aims to collate all the research findings related to these blade profiles/shapes and makes an attempt to highlight their features together with future recommendations.

Evolution and Progress in the Development of Savonius Wind Turbine Rotor Blades Profiles and Shapes

The utilization of urban wind energy through small wind turbines has become an arising technology to ease the conflicts between rising energy demands in buildings and depletion of traditional energy resources Many studies have reported that drag type vertical axis wind turbines have superior performance in the unsteady wind because of their attractive features Several review studies have been conducted on these turbines They mainly focused on the geometrical design parameters, the flow patterns, the research methodology, and the wind tunnel blockage correction However, less research has been conducted to classify the Savonius rotor based on the classification criterion of the blade profile and has made a comprehensive performance comparison between different types of Savonius rotors The blade profile is the essential design issue for a Savonius rotor; therefore, the variation of the blade profile will change the design parameters and affect the rotor's performance significantly So, the classification based on the blade profile can not only present the effect of key design parameters on rotor's performance for each blade profile easily but also obtain the functional features of different profiles and the comparison among different profiles Hence, in this article, we aim to summarize the classification of Savonius wind turbines according to the blade profile and present the development of this promising low speed generator

Review of the Savonius rotor's blade profile and its performance

In this paper a new bucket configuration for a Savonius wind generator is proposed. Numerical analyses are performed to estimate the performances of the proposed configuration by means of the commercial code COMSOL Multiphysics® with respect to Savonius wind turbine with overlap only. Parametric analyses are performed, for a fixed overlap ratio, by varying the slot position; the results show that for slot positioned near the blade root, the Savonius rotor improves performances at low tip speed ratio, evidencing a better starting torque. This circumstance is confirmed by static analyses performed on the slotted blades in order to investigate the starting characteristic of the proposed Savonius wind generator configuration.

Slotted blades savonius wind turbine analysis by CFD

In this paper a new bucket configuration for Savonius wind generator is proposed. With the aim to increase the effect of the overlap ratio RS on the wind turbine performances and to increase the amount of lift force able to produce torque and power, slotted blades are investigated by means of the Computational Fluid Dynamics analysis. The numerical analyses are performed by Comsol Multiphysics® and the results obtained for a Savonius wind turbine with overlap only are compared to numerical and experimental benchmarks. Parametric analyses are performed, for fixed overlap ratio, by varying the slot angle β and the results show that for low angle β the Savonius rotor exploits improved performance at low tip speed ratio λ, evidencing a better starting torque. This circumstance is confirmed by the static analyses performed on the slotted blades in order to investigate the starting characteristic of the proposed Savonius wing generator configuration.

Flavio Trentacosti

Papers

Slotted blades savonius wind turbine analysis by CFD

On the Effect of Slotted Blades on Savonius Wind Generator Performances by CFD Analysis