Optimization of Multi-Element Airfoils

Abstract
A review of techniques aimed at maximizing C1/Cd and C1 for multi- element airfoils showed the need for more exhaustive testing of possible configurations of flap deflection, slot geometry and airfoil angle of attack. For a typical 4-element airfoil, the number of possible configurations can easily be in the billions. A new technique, based on evolution strategy, has been developed for the problem of optimizing a multi-element airfoil with respect to its envelope of maximum C1/Cd versus C1. This technique was applied to an airfoil having a slotted leading edge flap and a double-slotted trailing edge flap using an existing computer program for 2D subsonic multi-element airfoils to provide values of aerodynamic coefficients. Although limitations of the program precluded the full determination of the envelope of C1/Cd vs C1 the problem of maximizing C1/Cd for a minimum C1 constraint was solved. The result of testing approximately 400 configurations generated by the random mutation- natural selection procedure of evolution strategy was an 8-fold increase in C1/ Cd iwth a 12% increase in C1 over the initial geometry.

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