Flow Control Mechanism Investigation on Prepositive Elliptical Wing-Main Wing Composite Configuration Based on Mode Decomposition

The composite design of the prepositive elliptical wing-main wing configuration suppresses the flow separation on the main wing by harnessing the beneficial interference of airflow between the two wings. Employing computational fluid dynamics (CFD) and optimization technologies, the two-dimensional composite configuration enhances the overall lift-drag ratio by a remarkable value of 112.24% compared to the baseline airfoil at an angle of attack of 18°, with a 74.41% increase in the time-averaged lift-drag ratio during a pitch oscillation period. To decipher the underlying flow control principles, numerical simulation-derived transient flow field snapshots are analyzed through the proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD). For the static conditions, the vortex shedding from the elliptical wing is critical in achieving the desired flow control effects. A necessary prerequisite for the effective creation of this vortex is the slit created between the main wing and the elliptical wing. For the dynamic conditions, the airflow acceleration facilitated by the slit is the predominant factor in the flow control effectiveness of the composite configuration. The vortex shedding that takes place downstream of the elliptical wing complements this primary effect, contributing as a secondary mechanism to the overall flow control. These results reveal the distinct mechanisms behind the flow control of the composite configuration under static and dynamic stall conditions and provide a theoretical foundation for this innovative approach to flow control.