An experimental study of stall delay on the blade of a horizontal-axis wind turbine using tomographic particle image velocimetry

Abstract

Volumetric velocity fields were measured, for the first time, using Tomographic Particle Image Velocimetry (Tomo-PIV) on a model of the rotating blade of a 5kW horizontal-axis wind turbine (HAWT) to study the stall delay phenomenon at two different global tip speed ratios (TSR) of 3 and 5 with Reynolds number (Re) ≈5000. Static pressures were also measured and results illustrated higher suction peaks on the rotating blade than those on the static airfoil, which is typically observed for stall delay. Rather than the recirculation bubbles with strong reversed flows for the static airfoil at stall, attached flows were observed on the suction surface of the rotating blade. Radial flows from blade's root to tip were also found with strong spanwise velocity component, located in the vicinities of the vortices and close to the blade's suction surface. In contrast to the airfoil case, the vortices shed from the blade's edges were not found to break down into smaller ones. Blade's surface streamlines were also presented. At large angles of attack (AOAs), Coriolis forces were found to be larger than centrifugal forces in chordwise direction in all three measurement volumes, which contributes to the reduction of the adverse pressure gradient.