Flow Physics and Performance of Vertical Axis Wind Turbine Arrays

Abstract

Modern wind farms employing horizontal-axis wind turbines (HAWTs) require significant turbine separation to avoid aerodynamic interference, leading to inefficiencies in the use of wind resources and land area. On the other hand, arrays of vertical axis wind turbines (VAWTs) have the potential to achieve higher power output per unit land area because of their smaller footprint. Recent studies by Dabiri and co-workers have indicated that additional benefits can be obtained by optimizing the placement and the direction of rotation of VAWTs. The focus of the current work is to study the flow physics and performance of VAWT arrays using numerical simulations based on the Reynolds Averaged Navier Stokes equations. The results show that the majority of the wake deficit is confined to a few diameters downstream of a single VAWT and its spatial extent is seen to diminish with increased rotational speed. The extent of wake deficit extends further downstream by placing multiple VAWTs in a single column, irrespective of the direction of rotation of individual turbines. The aerodynamic interference between turbines gives rise to regions of excess momentum between the turbines, which leads to a significant augmentation up to twice that of an isolated turbine. Studies of VAWTs arranged in multiple columns show that the downstream columns can actually be more efficient than the leading column when spaced optimally.