High Angle of Attack Aerodynamics
Summary
Airfoil Flows
All aifoils stall past a critical angle of attack (angle corresponding to the maximum lift). The (static) stall characteristics depend on the design (thickness, leading edge radius, camber, trailing edge angle) and conditions of operation (ground, out of ground, etc.).
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Figure 1: static stall on airfoil
Wing Rock
Wing rock is a rolling oscillation due to loss of damping at high angles of
attack. This often leads to loss of control. Two particularly important cases are the
highly swept wing and the slender body wing rock (for ex. forebody-delta wing).
Important reviews of the problems are available in Orlik-Ruchemann (1983), Ericsson
(1995), Katz (1998). See below for more.
One of the features of high angle of attack flows is the appearance of asymmetrical
patters and thus non symmetrical loads (rolling moment, yawing moment, side force, etc.).
One case widely studied is the prolate spheroide.
Fig. 2 below shows how the breakdown in the symmetry flow on a wing-body combination
can be tackled. By using a spiral trip on the fuselage both ywa and rolling moments can
be greatly improved at hight angles of attack
Figure 2: yawing and rolling moment on wing-body combination.
An extreme case of high angle of attack aerodynamics is the atmospheric entry of the
Space Shuttle (about 40 deg at hypersonic speeds M > 20).
High-alfa effects are particularly pronounced on delta wings, on which they have
been studied for a wide range of aspect-ratio, Reynolds and Mach numbers. Three cases
are of special interest: leading edge separation; separation with shock;
shock-induced separation.
Breakdown of Symmetric Flow
Separation Characteristics
Related Material
Selected References
Specialised publications on request.
