Research on Multimodality in Aerodynamic/Stealth Airfoil Design Optimization

The airfoil on modern fighters needs large positive moment to maintain longitudinal trim in addition to good aerodynamic and stealth performance. The novel design requirements would increase the likelihood of multimodality in design space. To address this issue, this paper uses parallel niching method to identify the existence and possible sources of multimodality in the aerodynamic and stealth shape optimizations based on a symmetrical airfoil. To isolate the instances of space multimodality, several subproblems are studied by varying the number and range of design variables, as well as positive moment constraints, respectively. The results demonstrate that the occurrences of multimodality in aerodynamic design space are highly related to positive moment constraint and ranges of design variables. Additionally, it’s found that some local minimums in aerodynamic space are very close to that of stealth space, indicating that the there’s not that large conflict between aerodynamic and stealth design under certain circumstances. This discovery may appeal a new approach of aerodynamic/stealth design of aircraft.