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Genetic algorithms (GAs) are an optimal search
technique based on "evolutionary programming"
techniques that mimic Darwin's idea of "natural
selection." Ongoing research has demonstrated that
GAs are useful tools in aerospace design. Recent
research has centered on using GA-based-methods
for airfoil design. A "practical" problem of rotorcraft
industry origin that involved the vertical tail (NACA
63-418 airfoil section) of a current Army helicopter
was considered. The vertical tail was experiencing
buffeting within its normal flight envelope, and
excessive flow separation at moderate angles of
attack was a suspected cause. The objective of this
effort was to design a new GA-based vertical tail
airfoil section that maintained attached flow. The
associated shape-design problem was as follows:
minimize airfoil drag while retaining the thickness,
lift, and moment of the NACA 63-418 airfoil. An
additional constraint ensured that the new airfoil
design retained attached flow at three flight conditions
(at angles of attack of -2, 4, and 12 degrees, and
at a Mach number of 0.06). A simplified aerodynamic
analysis, the panel method, was to be used to keep
computational expense low.
Compared to the NACA 63-418 airfoil, the new
GA-based airfoil (figure 1) featured a maximum
thickness location that was farther forward; it also
had a more complex camber distribution. Results
showed that the new GA-based airfoil exhibited
similar lift, a smaller pitching moment, and less flow
separation than the NACA 63-418. Figure 2 shows
that at an angle of attack of 12 degrees, the separation
location improvement for the new GA-based
airfoil was 18% of the chord. Further analysis using
two more advanced codes (Ames ARC2D and the
Massachusetts Institute of Technology's XFOIL)
confirmed the above improvement (however, the
three codes predicted different improvement levels).
To summarize, it is believed that the present
GA-based procedure can be used for solving
rotorcraft-related problems of a practical nature.
Point of Contact: S. Kottapalli
(650) 604-3092
skottapalli@mail.arc.nasa.gov
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Fig. 1. NACA 63-418 design and new, genetic-algorithm-
based design.
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Fig. 2. Upper surface separation locations: angle of
attack = 12 degrees (NACA 63-418 design and new
design).
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