Flow-field and Noise Characterization of a Controlled-Diffusion Airfoil subject to flow separation and stall

The present experimental investigation in the anechoic wind tunnel of university of Sherbrooke focuses on the flow-field and noise characterization of a Controlled Diffusion (CD) airfoil, with the flow transitioning from an attached boundary layer at 15◦ incidence to a completely detached one (deep stall) at 22◦ incidence. Simultaneous unsteady wall-pressure and far-field measurements are performed to investigate the effect of Reynolds number on the separation and stalling noise signature of the CD airfoil. Spanwise coherence exhibits a bi-modal shape with levels of coherence shifting towards lower frequencies and increasing in value with increasing incidences. Spanwise wall-pressure correlation length estimated using Corcos model is found to be approximately 12 mm at 40 m/s and 5 mm at 16 m/s at stalling conditions. Far-field noise scales well with Strouhal number based on chord and U5, indicating a compact dipolar scaling for separation and stall noise mechanisms.