Vortical patterns in the wake of an oscillating airfoil

Abstract

The vortical flow patterns in the wake of a NACA 0012 airfoil pitching at small amplitudes are studied in a low-speed water channel. It is shown that a great deal of control can be exercised on the structure of the wake by the control of the frequency, amplitude, and also the shape of the oscillation waveform. An important observation in this study is the existence of an axial flow in the cores of the wake vortices. Estimates of the magnitude of the axial flow suggest a linear dependence on the oscillation frequency and amplitude. flutter problems. This theory later found extensive use in bio- fluid-dynamics, because the propulsion of certain species of birds, insects, and aquatic animals is characterized by a heaving and pitching motion of a high aspect ratio wing or fin.3-4 The main ingredients of the classical analysis are the two-dimensional potential flow along with linearized boundary conditions, small perturbation velocities, and the assumption of a planar vortex wake. The effects of nonlinear processes such as rolled-up wake patterns have been addressed using numerical techniques.5-7