The flying wing aircraft suffers from severe flow separation and leading-edge vortex breakdown at high angles of attack, which significantly deteriorates the aerodynamic performance and flight stability. This paper investigates the control mechanism of synthetic jet on the unsteady separated flow over the flying wing aircraft using the delayed detached eddy simulation (DDES) method. The effects of jet frequency and momentum coefficient on aerodynamic coefficients, vortex breakdown location, and flow field structures are systematically analyzed. Furthermore, the spectral proper orthogonal decomposition (SPOD) method is employed to extract the dominant coherent modes and their frequency characteristics under both baseline and controlled conditions. The results show that synthetic jet control effectively suppresses flow separation and delays vortex breakdown, with control effectiveness strongly dependent on excitation frequency. Low-frequency excitation at F⁺ = 1.02 achieves the best overall performance, increasing the lift coefficient by 14.9% from 0.956 to 1.098. In contrast, high-frequency excitation at F⁺ = 10.20 shows limited effectiveness as the perturbations fail to inject the main vortex core. Increasing the jet momentum coefficient enhances control performance up to a threshold, beyond which additional momentum injection yields no further improvement. The SPOD analysis reveals that low-frequency control establishes the frequency locking at the excitation frequency with the first mode energy proportion reaching 0.92, effectively suppressing the baseline vortex breakdown mode, while high-frequency control fails to achieve such locking.
