Comparative Analysis of the Impact of Two Flow Control Methods on the Stall Characteristics of <scp>NACA0021</scp> Airfoil Using <scp>DMD</scp> and <scp>POD</scp> Methods

ABSTRACT In aerospace engineering and wind turbine applications, flow control technologies improve the behavior of separated flows around airfoils by employing diverse methods. However, the effectiveness of these methods varies significantly. Therefore, it is necessary to conduct an in‐depth analysis of the flow structure over the airfoil surface after applying flow control. This helps to gain a deeper understanding of the underlying physical mechanisms, thereby providing a theoretical basis for optimizing flow control techniques and guiding the selection of the most appropriate flow control strategies according to specific requirements. This study utilized the delayed detached eddy simulation (DDES) technique to simulate the detailed flow field around a NACA0021 airfoil under two common flow control strategies: The Gurney flap and the combined leading‐ and trailing‐edge flaps, both tested at a stall angle of attack of 20°. Subsequently, dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD) were employed to analyze the flow structure characteristics derived from velocity field data. This analysis exposed the distinct patterns and mechanisms through which these two methods modulate the unsteady flow field on the airfoil surface during stall conditions and clarified the intrinsic differences in their impact on the airfoil's aerodynamic properties. Highly instructive for in‐depth study of flow control methods.