Low-Reynolds-number effect on the aerodynamic characteristics of a pitching NACA0012 airfoil

Abstract

The effect of a low Reynolds number in the range of 2.0×104<Rec<5.0×104 on the aerodynamic characteristics of a pitching NACA0012 airfoil was investigated. Reverse flow and near wake were visualized by smoke-wire flow visualization, and lift and pressure drag coefficients were estimated by measuring unsteady pressure through pressure distortion correction. A NACA0012 airfoil sinusoid-pitched at quarter chord was employed, and its mean angle of attack and oscillation amplitude were α=0° and 6° respectively. The test Reynolds numbers were Rec=2.3×104, 3.3×104 and 4.8×104 with a fixed reduced frequency of K=0.1. Through reverse flow visualization, the first and second trailing-edge vortices and mushroom structure depending on the Reynolds number were observed. In lift and pressure drag coefficients, hysteresis loops were comparatively varied with the Reynolds number. As a result, the phase angle, at which boundary-layer events occurred, was in inverse proportion to the increase in Reynolds number. This result implies that the increase in Reynolds number promotes the occurrence of boundary-layer events such as laminar separation and transition.