Abstract
Conventional HAWTs dominate the wind industry commercially, whereas VAWTs are receiving researchers’ interest now across the globe due to their inherent advantages over HAWTs. VAWTs are more suitable for the offshore environment due to their omnidirectionality and lower center of gravity. The centrifugal forces play a dominant role in the bending of the vertical axis wind turbine blades in addition to aerodynamic forces. Thus, there is a scope for the optimization of VAWT blades’ wall thickness and material such that the contributions of aerodynamic and centrifugal forces in the bending of blades are equalized. Further, the probabilistic nature of the wind causes more complexities in the system. So far, many studies have been performed employing computational fluid dynamics and FSI approaches to analyze VAWTs. However, only a few publications give insight into its structural behaviour as a result of interaction with the random nature of the wind velocity.
The present study is carried out in two steps. The first step involves the probabilistic analysis of the actual wind speed of 13 months (1 November 2017 to 30 November 2018) recorded using LIDAR in the Gulf of Khambhat, in the Indian Ocean. The probabilistic wind data is then used to estimate the wind-induced pressure on blades using the standard commercial CFD tool, ANSYS Fluent considering a three-bladed vertical axis wind turbine with a symmetrical NACA airfoil. The aerodynamic pressure is estimated based on the Reynolds-Averaged Navier Stokes (RANS) equations.
The latter part of the study involves structural analysis of the hollow composite blades of VAWT due to the aerodynamic pressure estimated from the first part and centrifugal forces due to rotation. The risk of failure arises due to the exceedance of stresses/strains beyond a threshold. Each hollow blade is modeled with different layers of material and thickness to minimize the blade mass such that the stresses/deflections are within the allowable limits and blades do not exhibit dynamic instabilities such as flutter. The study will be useful for an improved and efficient design of the VAWT in an Indian offshore environment.
