Improved Rotorcraft Airfoil Designs Using Genetic Algorithms

摘要

Genetic algorithms (GAS) are an optimal search technique based on evolutionary programming techniques that mimic Darwin s idea o i natural selection. Ongoing research has demonstrated that CAS are useful tools in aerospace design. Recent research has centered on using CA-based-methods tor airfoil design. A practical problem ot 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. 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 CA-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 Compared to the NACA 63-418 airfoil, the new 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.