Near-Wake Characteristics of an Oscillating NACA 4412 Airfoil

Abstract

An experimental study is carried out to investigate the near-wake characteristics of an airfoil oscillating in pitch. An NACA 4412 airfoil is sinusoidally pitched about the quarter chord point between an angle of attack of -6 and +6 deg. A hot-wire anemometer is used to measure the phase-averaged velocity and turbulence intensity in the near-wake region of an oscillating NACA 4412 airfoil. The freestream velocities of the present work are 3.4, 12.4, 26.2 m/s, the corresponding Reynolds numbers are 5.3×10, 1.9×10, 4.1×10, and the reduced frequency is 0.1. Streamwise velocity and turbulence intensity profiles are presented to show the Reynolds number effects in the near-wake region behind an airfoil oscillating in pitch. All the cases in these measurements show that the velocity defects are very large at the lowest Reynolds number of Re = 5.3×10, and are small at the other Reynolds numbers of Re = 1.9 × 10 5 and 4.1×10 in the near-wake region. __________________________________________ † Assistant Professor, ‡ Associate Professor Dept. of Aeronautical Science and Flight Operation * Associate Professor Department of Aerospace Engineering Copyright  2002 The American Institute of Aeronautics, Inc. All rights reserved. A significant difference in turbulence intensity between 5.3×10 and 1.9×10 is observed. This study shows that a critical value for the Reynolds number in the nearwake of an oscillating airfoil of the present work exists in the range between 5.3×10 and 1.9×10.