Spectral analysis of New MEXICO standstill measurements to investigate vortex shedding in deep stall

Abstract

Spectral analysis was performed on the time series data computed from pressure measurements on the New MEXICO (Model Rotor Experiments under Controlled Conditions) rotor in standstill conditions. As a priori, 3D airfoil polars were recreated from standstill measurements and compared against 2D airfoil polars and flat plate theory results to verify the measurements. The spectral analysis revealed the presence of dominant shedding frequencies for certain ranges of the geometric angle of attack. Two dominant shedding modes were identified: One was associated with bluff body vortex shedding, and the other was associated with low Strouhal number shedding. No dominant shedding frequencies were observed for angles of attack beyond 50°. The research improves on our current understanding of the unsteady nature of the stall regime, along with providing insight into the existence of vortex-induced vibrations on a wind turbine in standstill conditions.