Aerodynamic behavior and flow visualization on canonical NACA airfoils at low Reynolds number

Some unmanned aerial vehicles, micro-air vehicles, and small-scale wind turbines operate at Reynolds number values less than \(5 \times 10^5\) based on chord length. However, there are limited data sets characterizing the airfoil performance at Reynolds number spanning \(2\times 10^4 \le Re_c \le 5\times 10^4\). The objective of this study is to investigate the impact of airfoil thickness and camber for canonical NACA airfoils at Reynolds numbers in this range and to correlate the observed aerodynamic behavior with the flow patterns. For this purpose, NACA-0009, 0012, 0021, and 6409 airfoils were used, and all experiments were performed in a water tunnel. A high-precision load cell was utilized to characterize the performance of the airfoils, and the hydrogen bubble flow visualization was used to assess the flow over the airfoils. The results showed that the airfoil thickness and camber significantly influence the aerodynamic performance and a strong dependence on the Reynolds number was observed. Symmetric NACA airfoils exhibited nonlinear lift behavior at Reynolds number below \(4\times 10^4\) as well as abrupt changes in lift values. The cambered airfoil showed some Reynolds number dependence but performed better than its symmetrical counterpart. The aerodynamic performance was correlated with the observed flow features around the airfoils.