Performance Characteristics of a Vertical Axis Wind Turbine Operating in Different Environmental Conditions

Renewable energy is an essential source for arnessing natural forces such as wind energy in an age which is very conscious of the environmental effects of burning fossil fuels, and where sustainability is an ethical norm. Therefore, the focus is currently on both the adequacy of longterm energy supply, as well as the environmental implications of particular sources. In that regard, the near certainty of costs being imposed on carbon dioxide emissions in developed countries has profoundly changed the economic outlook of clean energy sources.
Wind turbines have vastly been developed in recent decades due to technology becoming more advanced. Since there is a continuous exhaustion of fossil fuels, it is of high interest with government encouragement to utilise wind technology. Wind turbines are currently advancing into cross-flow vertical axis operation, whereby research has shown a significant increase in performance compared to existing technologies. This research is based on the Savonius type Vertical Axis Wind Turbines (VAWTs). The VAWT design considered in the present study comprises of 12 rotor blades and 12 stator blades, where the wind speed of 4m/s has been considered. This wind speed is the average annual wind speed in Huddersfield, UK.
Erosion is a serious issue in Vertical Axis Wind Turbines that causes roughness on the blades via airborne dirt, debris and insects. Erosion has been shown to degrade the performance characteristics of a VAWT significantly. A number of different strategies have been employed to analyse erosion in VAWTs, and with the advent of powerful and advanced computational methods, it has become possible to investigate erosion at microscopic levels. Hence, this study is based on the predictions from numerical simulations performed using a Computational Fluid Dynamics based solver.
The first aspect of this study comprises of detailed numerical investigations on the performance evaluation of VAWTs operating in clean environments. Although many numerical studies are available in this particular area, however, most of these studies use rather simplified modelling techniques. The results presented in this study are based on transient modelling approaches, where instantaneous pressure and velocity fields have been computed and analysed.
Furthermore, instantaneous torque output of the VAWT has been recorded in order to develop a generic semi-empirical prediction tool that accounts for the variations in the geometric configurations of the VAWT.
The second aspect of this study is related to the erosion in VAWTs. This is of particular importance to VAWT designers who wish to install VAWTs in dusty environments, such as desserts, where wind velocities are significantly higher than in urban areas. Various dusty environmental conditions have been numerically created, comprising of different sand particle sizes and mass flow rates. Their effects on the performance degradation has been critically analysed in this study. Furthermore, erosion rates on rotor blades of the VAWT have been recorded. The results obtained have then been used in order to develop a novel semi-empirical prediction model for the torque generation from the VAWT that takes into account various sand particles’ parameters.