Visualization analysis of the starting flow around a pitching airfoil. (1st Report, Elliptic airfoil pitching at mid-chord)

The starting flows past an elliptic airfoil pitching at large incidences are examined by visualization experiments and numerical calculations. The study concerns two-dimensional incompressible cases where the chordal Reynolds number is between 10 super(3) and 10 super(4). The main object of the research is to reveal some fundamental phenomena specific to the unsteady airfoils in the so-called deep stall regime. The variable parameters considered are the pitching frequency, the mean incidence, the angular amplitude and the Reynolds number, of which the effects on the wake patterns will be discussed. It will be demonstrated in due course that the vortex formation, consequent to the pitching motion of the airfoil, is subject to two types of different fluid dynamics, which are dependent on the relative importance of the reduced frequency and the angular amplitude.