Copyright © A. Filippone (1999-2003). All Rights Reserved.

Highly Separated Airfoil Flow

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 surface.

  • 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.

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Copyright © A. Filippone (1999-2003). All Rights Reserved.