Performance and Wake Comparison of Horizontal and Vertical Axis Wind Turbines under Varying Surface Roughness Conditions

A numerical study of both a horizontal axis wind turbine (HAWT) and a
vertical axis wind turbine (VAWT) with similar size and power rating is
presented. These large scale turbines have been tested when operating stand‐alone at their optimal tip speed ratio (TSR) within a neutrally
stratified atmospheric boundary layer (ABL). The impact of three
different surface roughness lengths on the turbine performance is
studied for the both turbines. The turbines performance, the response to
the variation in the surface roughness of terrain, and the most
relevant phenomena involved on the resulting wake were investigated. The
main goal was to evaluate the differences and similarities of these two
different types of turbine when they operate under the same atmospheric
flow conditions. An actuator line model (ALM) was used together with
the large eddy simulation (LES) approach for predicting wake effects,
and it was implemented using the open‐source computational fluid
dynamics (CFD) library OpenFOAM to solve the governing equations and to
compute the resulting flow fields. This model was first validated using
wind tunnel measurements of power coefficients and wake of interacting
HAWTs, and then employed to study the wake structure of both full scale
turbines. A preliminary study test comparing the forces on a VAWT blades
against measurements was also investigated. These obtained results
showed a better performance and shorter wake (faster recovery) for an
HAWT compared with a VAWT for the same atmospheric conditions.