Numerical Study of Separation Control by Movable Flap

Lift coefficient over angle of attack for the clean HQ17 airfoil
predicted by different turbulence models (Re = 10⁶)

Numerical investigations of the clean airfoil show that the flow becomes unsteady at high angles of attack with a vortex street developing. To find an optimum flap angle, the resulting aerodynamic forces on the flap are calculated for each angle. A self-activated flap will stay in its equilibrium position where the sum of all forces on the flap is zero. By introducing such a flap, the flow can be stabilized and the maximum lift increases.


clean airfoil		flap angle = 25^o

flap angle = 40^o		flap angle = 52^o

At the optimum angle the flap is just slightly touching the detached shear layer. If the flap angle is too low, the flap remains inside the reverse flow region and shows less effect. In the case of too large angles, the flap works like a spoiler and generates additional drag. Compared to the clean airfoil the maximum lift coefficient can be enhanced by more than 10%. The predicted lift coefficients agree fairly well with the experimental data. Further investigations were carried out for different flap angles to find an optimum flap configuration for a given angle of attack.


Calculated lift coefficient for different flap angles		Calculated flap-force coefficient over angle of attack for different flap angles (C_F = 0 means flap in equilibrium position)

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Last modified: Mon Dec 13 14:46:01 CET 1999