Low-Reynolds-number airfoil design optimization using deep-learning-based tailored airfoil modes

Low-Reynolds-number high-lift airfoil design is critical to the performance of unmanned aerial vehicles (UAV). However, since laminar-to-turbulent transition dominates the aerodynamic performance of low-Reynolds-number airfoils and the transition position may exhibit an abrupt change even with a small geometric deformation, aerodynamic coefficient functions become discontinuous in this regime, which brings significant difficulties to the application of conventional aerodynamic design optimization methods. To efficiently perform low-Reynolds-number airfoil design, we present a tailored airfoil modal parameterization method, which reasonably defines the desired design space using deep-learning techniques. Coupled with surrogate-based optimization, the proposed method has shown to be effective and efficient in low-Reynolds-number high-lift airfoil design. It is found that it is necessary to consider laminar-to-turbulent transition and to perform multi-point optimization in practical low-Reynolds number airfoil design. The maximal lift coefficient is an active constraint influencing the selection of the optimal cruise lift coefficient. The results show the complexity of low-Reynolds-number high-lift airfoil design and highlight the significance of the proposed method in the improvement of optimization efficiency. (c) 2021 Elsevier Masson SAS. All rights reserved.