Multi-objective optimization of unconventional airfoils at low Reynolds numbers

The widespread exploration of drones has generated increasing interest in Micro Aerial Vehicles (MAVs). Furthermore, an application that has gained notoriety is the use of aerial vehicles for exploration on Mars. Thus, the quest for efficient aerodynamic profiles for these applications has been intensified. These types of applications operate in a Reynolds number range from 10^4 to 10^5, which is significantly smaller than those commonly found in conventional low Reynolds regimes, such as when commercial drones are adopted. The main objective here is to identify more efficient shapes for airfoils, optimizing them through a multi-objective process aiming to maximize the lift coefficient and minimize the drag coefficient. To achieve this goal, two models of unconventional airfoils were optimized using the Generalized Differential Evolution 3 (GDE3) algorithm. The acquisition of aerodynamic coefficients, essential for evaluating the performance of the evolutionary algorithm, was carried out through simulations using Computational Fluid Dynamics (CFD). The method applied to describe the aerodynamic behavior of the structures proved to be consistent with experimental data. We used two base structures: a cubic Bézier-profile plate and a planar model with two inflections. Employing the aircraft's range or autonomy as decision criteria, it was observed that the cubic Bézier-profile plate presented superior results. Analyzing the graphs of the aerodynamic coefficients in relation to the angle of attack, the considerable increase in the stall point and lift provided by this model is notable. Such improvements, however, were accompanied by a slight disadvantage in the drag coefficient for small or negative angles of attack. It was also found that the evolutionary algorithm resulted in aerodynamic profiles with interesting characteristics for these applications when compared to existing models in the literature. In conclusion, the proposed cubic Bézier-profile plate model proved to be an interesting alternative for applications with a significantly small Reynolds number.