Influence of Varying the Stage Aspect Ratio on the Performance of Multi-Stage Savonius Wind Rotors

Abstract

Although using a multi-stage rotor of Savonius vertical-axis wind turbine enhances the self-starting ability, it reduces the power coefficient. To improve power coefficient, the influence of varying the stage aspect ratio is investigated. Therefore, two-, three-, and four-stage Savonius rotors at stage aspect ratios ranging from 0.5 to 1.5 with increments of 0.25 are considered. To determine performance parameters such as coefficients of torque, power, and thrust, a comprehensive three-dimensional unsteady incompressible turbulent flow model using Reynolds-Averaged Navier-Stokes (RANS) equations along with k-ω shear stress transport turbulence model is developed. The developed numerical model is validated utilizing the available experimental results. Moreover, a novel assessment technique relying on flow field characteristics such as pressure distribution in conjunction with streamlines around the proposed multi-stage Savonius rotor with various stage aspect ratios is carried out. The contribution of each stage on the performance of the whole rotor is computed and presented. The findings of the current study illustrate that utilizing a multi-stage rotor with stage aspect ratio equal to or greater than 1.0 significantly enhances the output power. By rising the stage aspect ratio within the range of 0.5 to 1.5, the peak coefficient of power boosts from 0.163 to 0.213 for a two-stage rotor, and from 0.183 to 0.23 for a four-stage rotor. In addition, three-stage rotors with stage aspect ratio ranging from 0.5 to 1.5, shows increased average static coefficient of torque from 0.196 to 0.272 with positive values at whole rotation angles. This improves the self-starting abilities of the multi-stage rotor and makes it suitable in areas where the wind is intermittent and very low. Furthermore, raising the stage aspect ratio from 0.5 to 1.5 significantly mitigates the oscillations of both torque and thrust coefficients throughout the entire cycle for all multi-stages. This lowers the mechanical vibrations and noise emission during operation conditions. Accordingly, multi-stage Savonius rotors with stage aspect ratio equal to or greater than 1.0 are highly recommended for practical applications.

The Blade's Angle Affects Banki-Turbine Performance as an Alternative Design for Clean Energy Generation

“…The banki-turbine has a height (H) of 130 mm, an outer diameter (D) of 80mm, an inner diameter (d) of 60mm, and a thickness of 2mm. The zones in the banki-turbine model are divided into two, a rotating zone and a stationary zone [8,13,15]. The rotating zone is the runner zone and the rotating interface, and the stationary zone is the runner's home zone and boundary conditions.…”

“…Figure 5 shows the resulting mesh in the rotating zone and stationary zone. Mesh independence is used to get the best meshing [13,30]. Mesh independence is done by making changes to the mesh size [13].…”

“…Mesh independence is used to get the best meshing [13,30]. Mesh independence is done by making changes to the mesh size [13]. There are five types of settings that have been created.…”

“…The Savonius turbine and the banki-turbine are quite popular turbines developed because they both have a simple shape and can be operated using air or water fluids. Changes in geometry are still the primary research to improve turbine performance, such as PSA [13], Aspect Ratio [14], Number of blades [8,15], Overlap ratio [16], Number of stages [6], and shape of blade [3]. However, apart from the geometric aspect, several other factors also influence, such as the rotor material factor [17][18][19][20].…”

Enhancing Savonius Rotor Performance With Zigzag Surface Investigated at Drag Force, Pressure, and Flow Visualization Analysis

“…In order to maximize the Savonius rotor's efficiency experts have suggested numerous modifications and refinements to the design. They had examined the effects of diverse design characteristics, such as modification of blade shape [3], [4], [5], [6], variation of overlap ratio [7], [8], [9], endplates [10], [11], aspect ratio [12], number of stage rotors [12], and number of blades [9]. The primary focus of these studies revolves around the examination of the impact of various parameters on its performance.…”