Optimal Design of Auxetic Core Airfoil for Wing Morphing Applications

Abstract

Bird wings demonstrate phenomenal adaptation and aerodynamic performance across varied flight conditions. In contrast, conventional aircraft wings are designed for specific scenarios, limiting their adaptability. Therefore, the integration of smart structures into morphing airfoils is crucial for furthering aircraft development. One intriguing approach is the utilization of cellular auxetic configurations, which exhibit an inverse (negative) Poisson’s ratio, popularly recognized as auxetic behavior. This particular trait can bring substantial advantages to the morphing process. Morphing airfoils containing a cellular auxetic core offer various benefits, including greater deformability, ease of control, variable stiffness, and improved stress tolerance. This research provides a novel approach by discovering the optimal reentrant unit cell and extending its key advantage within the aerospace sector, focusing on achieving maximal wing trailing edge deflection. This research compares the morphing performance of the Eppler 420 airfoil incorporating different cellular auxetic cores, including hexagonal honeycomb, chiral honeycomb, and reentrant honeycomb configurations. A parametric investigation explores the in-plane characteristics of a 2D reentrant honeycomb configuration and evaluates the consequences of parameter changes on the structure’s negative Poisson ratio and elastic modulus. Through multi-objective optimization employing a genetic algorithm, the study achieves a remarkable 54.65% enhancement in Poisson’s ratio and a substantial 37.5% rise in the relative elastic modulus, as evaluated analytically. The Finite Element Analysis (FEA) of the Eppler 420 airfoil revealed that integration of the reentrant honeycomb configuration outperforms the other two configurations to achieve maximum trailing edge deflection or morphing. Furthermore, the incorporation of optimized reentrant configuration within the airfoil core leads to a significant augmentation of 21 % in trailing edge deflection compared to standard reentrant configuration. decoupled fluid structural analysis of the Eppler 420 airfoil showed that maximum morphing occurs at an 8° angle of attack with Mach 0.25 and a 6° angle with Mach 0.45. The optimized reentrant honeycomb configuration improved trailing edge deflection by 17.3% compared to the standard reentrant honeycomb core. This research emphasizes the potential of adopting optimized reentrant structures to boost the performance and adaptability of aircraft wings.