Aerodynamic optimization of an adaptive flap for next-generation green aircraft

Abstract

Adaptive, morphing flaps are taking ever-increasing attention in civil aviation thanks to the expected benefits this technology can bring at the aircraft level in terms of high-lift performance improvement and related fuel burnt reduction per flight. Relying upon morphing capabilities, it is possible to fix a unique setting for the flap and adapt the flap shape to match the aerodynamic requirements for take-off or landing. The proper morphed shapes can assure better high-lift performances than those achievable by referring to a conventional flap. Moreover, standing the unique flap setting for take-off and landing, a dramatic simplification of the flap deployment systems may be achieved. As a consequence of this simplification, the deployment system can be fully hosted in the wing, thus avoiding under-wing nacelles with significantly better aerodynamics and fuel consumption. The first step for a rational design of an adaptive flap consists in defining the target morphed shapes and the unique optimal flap setting in the take-off and landing phases. In this work, aerodynamic optimization analyses are carried out to determine the best flap setting and related morphed shapes in compliance with the take-off and landing requirements of a reference civil transport aircraft. Four different initial conditions are adopted to avoid the optimization falling into local optima, thus obtaining four groups of optimal candidate configurations. After comparing each candidate's performance through 2D and 3D simulations, the optimal configuration has been selected. 2D simulations show that the optimal configuration is characterized by a maximum lift increase of 31.92% in take-off and 9.04% in landing. According to 3D simulations, the rise in maximum lift equals 22.26% in take-off and 3.50% in landing. Numerical results are finally verified through wind tunnel tests, and the aerodynamic mechanism behind the obtained improvements is explained by carefully analyzing the flow field around the flap.