Numerical simulations of structural and fluid dynamics for aerodynamic performance improvement

The present research aims to understand and improve the aerodynamic performance of airfoils in unmanned aerial vehicle (UAV) and wind energy applications using numerical approaches. Specifically, the research applications include: 1) the flexibility tailoring of passively induced airfoil shapes for thin UAV wings, and 2) the aerodynamic performance evaluation of wind turbine blade airfoils that include idealized leading edge (LE) damage patterns aimed at emulating erosion. In both applications, fundamental insights that motivate subsequent optimum design configurations are sought through the use of computational tools of varying efficiency and fidelity. In regard to the first airfoil type studied, UAVs have attracted special attention in recent decades due to their unique and adaptable functionality for both military and civilian applications. Among fixed-wing UAVs, those with flexible passively-deforming wings have been shown to achieve extended aerodynamic endurance, reduced power consumption, and beneficial stability characteristics. Since neither excessively flexible nor excessively rigid wings maximize aerodynamic performance, flexibility tailoring for such membrane wings is still of significant interest. However, the numerical and experimental studies to date have been mostly limited to 2D studies, specifically to chordwise flexibility. To gain insights into furv ther design improvements, such as enabling extended aerodynamic endurance, more complex 3D geometric flexibilities, as are investigated and described in this work. Emulating a bioinspired flexible UAV wing design, a novel topology optimization using a genetic algorithm with an efficient fluid structure interaction (FSI) model produces a wing frame configuration with optimal flexibility distribution. The decoupled effects of the induced camber and spanwise bending deformation are analyzed to understand their contributions to performance improvements. Regarding the second airfoil type studied, designing wind turbine blades to achieve both extended service life and high operating efficiency is of great interest. Leading edge erosion, which poses significant problems to efficiency, necessitates research into the understanding of the underlying fluid dynamics. However, strong three-dimensionality of flow and relatively small scale of erosion poses great challenges to understanding and predicting the flow behavior numerically in terms of fidelity and computational time. Presented is a reduced order model (ROM) proposed for efficient drag prediction on a streamlined body with surface imperfections that emulate leading-edge roughness or erosion-induced damage. It requires as input only the geometric description of damage. Satisfactory performance is demonstrated via comparison with direct numerical simulations. Insights into the flow physics influencing both form and friction contributions to total drag are presented, a preferable damage mode from an engineering design aspect is revealed. In summary, the described work addresses the research gaps through applying a set of numerical tools with varying fidelity and efficiency to conduct investigations from the aspects of aerodynamic performance, geometric design, and optimization. The results of the research provide new understanding in how to improve aerodynamic performance in both airfoil application types.