Experimental Investigations of Dynamic Stall on a Pitching Airfoil at Moderate Reynolds Numbers

The unsteady aerodynamics of stall play a key role in determining the performance of engineered and biological flight systems, wind turbines, etc. An airfoil undergoing a rapid pitching motion in which its angle of attack increases above its static stall angle experiences a phenomenon known as dynamic stall, in which aerodynamic forces and moments exhibit large deviations from their steady values. In the present work, the flow around a pitching NACA0021 airfoil is investigated using Particle Image Velocimetry with a focus on the mechanisms of stall, the time scales of dynamic stall events, and associated flow features. Experimental conditions cover reduced frequencies up to 0.1 for chord-based Reynolds numbers up to 2.5 × 10⁵. This work complements similar studies performed in the High Reynolds number Test Facility.