energies Article Effect of Helix Angle on the Performance of Helical Vertical Axis Wind Turbine Unnikrishnan Divakaran 1 , Ajith Ramesh 1 , Akram Mohammad 2 and Ratna Kishore Velamati 1, *   Citation: Divakaran, U.; Ramesh, A.; Mohammad, A.; Velamati, R.K. Effect of Helix Angle on the Performance of Helical Vertical Axis Wind Turbine. Energies 2021, 14, 393. https://doi.org/10.3390/en14020393 Received: 26 November 2020 Accepted: 8 January 2021 Published: 12 January 2021 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional clai- ms in published maps and institutio- nal affiliations. Copyright: © 2021 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Mechanical Engineering, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Coimbatore 641112, India; d_unnikrishnan@cb.amrita.edu (U.D.); r_ajith@cb.amrita.edu (A.R.) 2 Department of Aeronautical Engineering, Faculty of Engineeirng, King Abdulaziz University, Jeddah 21589, Saudi Arabia; ammohamad4@kau.edu.sa * Correspondence: v_ratnakishore@cb.amrita.edu Abstract: The energy crisis has forced researchers to look for various non-conventional energy sources. Wind energy is one of the potential sources, and researchers have invested resources in developing different kinds of wind turbines. Vertical axis wind turbines (VAWT) have received less attention than their horizontal-axis counterparts. A helical-bladed VAWT is preferred because it makes perfect sense as an improvement in design, as they have higher azimuth angles of power generation capabilities. This paper studies the effects of the helix angle of blades in the aerodynamic performance of VAWT using 3D numerical simulations. Three different helix angles of 60 ◦ , 90 ◦ , and 120 ◦ of a three-bladed VAWT operating across different tip speed ratios were studied. Turbulence is modelled using a four-equation transition SST k-ω model (shear stress transport). The 60 ◦ helical- bladed VAWT was found to be better performing in comparison with all other helical-bladed and straight-bladed VAWT. The ripple effects on the shaft are also analysed using a standard deviation plot of the moment coefficient generated by a single blade over one complete cycle of its rotation. It was observed that the greater the helix angle, the lower the standard deviation. The paper also tries to analyse the percentage of power generated by each quartile of flow and the contribution of each section of the blade. Ansys FLUENT was employed for the entire study. A comparative study between different helical-bladed VAWT and straight-bladed VAWT was carried out along with wake structure analysis and flow contours for a better understanding of the flow field. Keywords: vertical axis wind turbine; wind energy; helical blade; CFD 1. Introduction Unhindered access to electric power is one of the most important factors ensuring the dynamic development of the countries and civilisations. Since the start of 20th century, fossil fuels have been considered as the most common energy carrier, which has caused a rapid growth of civilisation. However, due to ecological and economic issues, many countries are introducing new regulations to cut down the utilisation of fossil fuels and emission of CO 2 [1–3]. According to these regulations, most of the states have committed to increase their fraction of the generation of the renewable sources of energy of the total installed electric power generation capacity. The wind energy can be a good alternative for fossil fuels, as it can help reduce the consumption of fossil fuels and emission of flue gases. The main disadvantage of using wind energy is its high sensitivity to the forecast conditions [4,5]. This disadvantage makes it difficult to control and foresee wind energy production. Other disadvantages are noise generated by wind turbines [6] as well as their visual [7] and environmental [8] impact (behaviour of animals, especially birds) on the surrounding. Some of the above problems can be overcome by decentralised application of vertical axis wind turbines (VAWTs), which are less sensitive to the wind conditions and have a broader range of operational wind speed. There are certain studies that prove Energies 2021, 14, 393. https://doi.org/10.3390/en14020393 https://www.mdpi.com/journal/energies