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

The effect of a low Reynolds number in the range of 2.0 x 10(4) < Re-c < 5.0 x 10(4) 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 alpha = 0 degrees and 6 degrees respectively. The test Reynolds numbers were Re-c = 2.3 x 10(4), 3.3 x 10(4) and 4.8 x 10(4) 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. Crown Copyright (C) 2013 Published by Elsevier Masson SAS. All rights reserved.