Dynamic stall events in presence of massive separation are described below.
At low angle of attack the flow is fully attached, with viscous layer of limited
extent; Lift coefficient and pitching monet follow the trend of the linear regime.
the aerodynamic center is frozen at one quarter chord location.
Upstroke: the angle corresponding the maximum static lift is exceeded; flow
reversal appears, but forces and moments still follow a linear trend featuing a
time lag between actual flow conditions and angle of attack.
Breakdown in the pitching moment occurs; the center of pressure moves aft and the
pitching moment soon diverges; flow structure: the primary vortex detaches from the
Time delay is exceeded; massive separation occurs; the primary vortex travels
towrd the trailing edge; secondary vortices and leading edge serapation appears;
lift increases at a faster rate.
The primary vortex is downstream the trailing edge; maximum lift and negative pitching
moment are reached, followed by rapid decay.
Secondary vortices are likely to be present on the pressure side of the airfoil.
Downstroke: Lift reaches value corresponding to fully separated flow and
tends to re-adjust to linear regime.
At lower angle of attack the flow reattaches and re-adjustes to its prior value close
to the static lift curve.