Unsteady aerodynamic response mechanism of double-delta wing under high angle of attack

Abstract

This study conducts a numerical investigation into the unsteady characteristics of a 80°/65° double-delta wing at high angle of attack using delayed detached-eddy simulation. By combining power spectral density analysis and dynamic mode decomposition, the characteristic frequencies and spatial patterns of the dominant vortex motions are identified, and their frequency-resolved relationships with the associated aerodynamic responses are revealed. Near the strake–main-wing junction, the strake-vortex system interacts with the main-wing leading-edge shear layer and develops into a dominant primary vortex downstream, while a weaker counter-rotating secondary vortex remains near the main-wing leading edge. As the primary vortex develops downstream, vortex breakdown occurs, accompanied by the formation of helical structures. The unsteady motions in the entire flow field can be categorized into three distinct frequency bands: low-frequency, medium-frequency, and high-frequency oscillations. The dominant unsteady motions are organized into a low-frequency harmonic family associated with vortex breakdown point oscillation (Stf≈0.0199, 2Stf≈0.0398), a medium-frequency mode associated with downstream helical structures(St≈0.619), and a high-frequency mode associated with primary vortex axis motion(St≈0.859). In terms of aerodynamic response, the unsteady fluctuation of normal force is dominated by low-frequency vortex breakdown point motion and medium-frequency helical structure motion, whereas the pitching moment is jointly affected by all three bands of oscillations.