Optimum power generation assessment in an H-Darrieus vertical axis wind turbine via Exergy Destruction Minimization

Abstract

In recent years, Vertical Axis Wind Turbines have emerged as a viable complement to the ever-expanding worldwide wind power generation. Compared to conventional wind turbines, they are independent of wind direction, emit less noise, and require a smaller installation area, making them attractive for urban and remote implementations. In this work, a Second Law of Thermodynamics approach is utilized to deepen the understanding of the fluid dynamics phenomena that reduce the turbines' power generation. The turbulent unsteady fluid flow around the turbine is computed using a two-dimensional Finite Volume approach via the commercial software ANSYS Fluent, which is validated using experimental data available from the literature. The Exergy Destruction and the Reversible Work grow in direct proportion to the flow speed, although their growth rate depends on the turbine operating regime: attached flow or dynamic stall. The latter explains how the Second Law Efficiency maximizes at an intermediate Tip Speed Ratio, which coincides with a more efficient power generation.