Michael J. Candon

Evolutionary optimization of transonic airfoils for static and dynamic trim performance

The development and accelerated use of optimization frameworks in aircraft design is a testament to their ability to identify optimal and often non-intuitive shapes as a result of multi-disciplinary design objectives. Airfoil design is a continuously revised multi-disciplinary problem, and is pivotal to illustrate the performance of optimization frameworks involving numerical simulation, flexible shape parametrization, and intelligent evolutionary algorithms. An often overlooked component of this classic problem is to consider the dynamic aeroelastic behavior under trim conditions, which can generate explicit boundaries to the flight envelope. Trim introduces a significantly strong coupling with objectives governing static performance, e.g. aerodynamic and/or structural, thereby resulting in a highly nonlinear and discontinuous design space. In this paper, a multi-objective particle swarm optimization framework for multi-disciplinary performance improvement is presented, pertaining to aerodynamic, structural and aeroelastic design criteria at trim conditions. The framework is assisted by the construction of adaptive Kriging surrogates, which is cooperatively used with the numerical solver to identify optimal solutions within a computational constraint. Designer preferences are introduced to reflect the optimal compromise between the objectives. Results of the optimization process indicate a large spread in design variable influence and interaction, and a subtle yet clear distinction between all objectives is illustrated through the catalog of final airfoil candidates obtained.

Identification of Nonlinear Aeroelastic Behavior of a Wing with Pitching and Plunging Freeplay via Higher-Order Spectra Analysis

Higher-order spectra (HOS) analysis is utilized to analyze the nonlinear flutter aspects of the AGARD 445.6 wing with pitching and plunging freeplay nonlinearities installed at the root. High-fidelity fluid-structure interaction simulations are conducted and the transient responses are monitored at the root and tip of the wing. The transient responses are truncated such that only the static portion of the signal remains and the HOS are evaluated. The pitching / plunging freeplay ranges of motion and initial setting angle are varied, and the effect on nonlinear interactions and transient response are monitored. It is demonstrated that the presence of pitching freeplay is a major driver in the nonlinear phenomena, that the amplitude of the LCO is highly sensitive to the plunging freeplay range of motion whilst the presence of nonlinear interactions are dependent on interactions between the pitching and plunging freeplay effects. The application of this methodology from a practical perspective includes structural health monitoring, and the ability to identify and mitigate undesirable nonlinear aeroelastic phenomena in the design phase.