Large Eddy Simulation of Helical- and Straight-Bladed Vertical Axis Wind Turbines in Boundary Layer Turbulence

Abstract

Turbulent wake flows behind helical-bladed and straight-bladed vertical axis wind turbines (VAWTs) in atmospheric boundary layer are studied numerically using the large-eddy simulation (LES) method combined with the actuator line model. Based on the LES data, systematic statistical analysis are performed to explore the effects of blade geometry on the characteristics of the turbine wake. The time-averaged velocity fields show that the helical-bladed VAWT generates a mean vertical velocity along the center of the turbine wake, which causes a vertical inclination of the turbine wake and alters the vertical gradient of the mean streamwise velocity. Consequently, the intensities of the turbulent fluctuations and Reynolds shear stresses are also affected by the helical-shaped blades when compared with those in the straight-bladed VAWT case. The LES results also show that reversing the twist direction of the helical-bladed VAWT causes the spatial patterns of the turbulent wake flow statistics to be reversed in the vertical direction. Moreover, the mass and kinetic energy transports in the turbine wakes are directly visualized using the transport tube method, the comparison between the helical- and straight-bladed VAWT cases show significant differences in the downstream evolution of the transport tubes.