Experimental study of airfoil aerodynamics at high Reynolds numbers

As offshore wind turbines trend toward larger dimensions for increased power output, there has been a corresponding rise in catastrophic blade-structure failure and fatigue that has increased both the capital cost and general uncertainty surrounding this burgeoning technology. The cause for these failures is now pointing toward the blade aerodynamics, understood largely to be uncharted territory for the difficulty associated with obtaining experimental data at full-scale, high Reynolds number operating conditions. This work will present both static and dynamic experimental aerodynamic results for the NACA0021 airfoil at chord Reynolds numbers 5 × 10⁵ ≤ Re_c ≤ 1 × 10⁷ and reduced frequencies 0.1 ≤ k ≤ 1. Aerodynamic forces were measured using surface pressure taps. This range of Re_c was achieved using the High Reynolds number Test Facility (HRTF) at Princeton University, which can operate at up to 220 bar pressure of the working fluid. This enables high Reynolds numbers with relatively low freestream velocities, U_∞ < 10 m/s (Ma < 0.03). As such, the results presented are devoid of Mach effects and have feasible pitching timescales. This study provides some of the first unsteady aerodynamic data at Reynolds numbers relevant to modern wind turbines.