Finite element modeling of structural design optimization of various vertical axis wind turbine models

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Wind is among the most popular and fastest growing sources of alternative energy in the world. It is an inexhaustible, indigenous resource, pollution-free, and available almost any time of the day, especially in coastal regions. Vertical axis wind turbines (VAWTs) are more practical, simpler, and significantly cheaper to build and maintain than horizontal axis wind turbines (HAWTs). They have other inherent advantages; for example, they always face the wind; can run at low wind speed without any starting torque. As well, they may even be critical to mitigating the grid interconnection stability and reliability problems that currently face electricity producers and suppliers. Cheap VAWTs may provide an alternative to destroying rainforests to grow biofuel crops. The purpose of this study is to perform a finite element static stress analysis to develop structurally stable and relatively efficient vertical axis wind turbine (VAWT) model design. VAWTs are typically used for lower wind speeds as opposed to HAWTs which are used in commercial wind farms that are used to produce a high energy output. For the finite element simulation, three different VAWT models such as conventional Savonius rotor, Helical Savonius rotor, and the Giromill type VAWT were considered. For the first two types VAWTs, rotation occurs due to the drag force generated due to the pressure difference between the concave and convex surfaces of the turbine blades. Whereas for the Darrieus rotor or Giromill type VAWT, rotation occur due to the lift force generated by the wind blowing past the airfoil shaped blades. The ANSYS FLUENT, a finite element based computational fluid dynamics solver, is adopted to obtain the pressure distributions on the Savonius type models and the lift force for the Giromill model. Each of the VAWTs is tested in ANSYS static structural modeler with three different types of materials such as aluminum alloy, stainless steel, and PVC. Also the Giromill turbine model is tested using two different types of airfoils that have two different lift coefficients. Comparison of the symmetric NACA 0012 and NACA 0714 airfoils of unit chord were chosen for the analysis of the Giromill model design. In this analysis, the airfoils were not allowed to move and the pitch angle of airfoil was assigned to the air flow at the inlet boundary of the domain. The goal of the numerical simulation was to determine the location and magnitude of maximum equivalent stress and total deformation of the blades of each model to determine the structural stability improvement and efficient design of the VAWT models. In all cases, the stainless steel made model deformed the least while aluminum model had a few more in deformation and PVC model experienced the highest amount of deformation. This was expected because PVC was the lightest of all the materials used in this study. The stresses were about the same for each case except for the NACA 0012 airfoil type.