The excitation induced by the wake from the upstream blade row is identified as the dominant cause of blade vibration. In the present work, a type of excitation induced by wake–separation-bubble interaction—which propagates at a velocity significantly slower than both the local speed of sound and the mainstream convective speed—is investigated. Large Eddy simulation and unsteady Reynolds-averaged Navier–Stokes simulations were employed to elucidate the formation and propagation mechanisms of this unsteady excitation. The boundary layer and turbulence field were analyzed and correlated with the unsteady pressure behavior. The results indicate that as the wake sweeps past the leading edge, its negative jet effect induces localized fluid acceleration on the suction surface, generating unsteady pressure perturbations. These perturbations amplify and destabilize the separation bubble via the Kelvin–Helmholtz instability, forming a shedding cell of low-pressure fluid. This cell evolves into a sustained low-pressure pattern propagating at approximately 50% of the mainstream velocity. An acoustic analysis further decomposes the pressure perturbations into two components: (1) nonlinear aerothermal processes and (2) local acceleration effects. Parametric studies demonstrate that reducing the size of the separation bubble—via geometric modifications of the leading edge—directly reduces both the spatial extent and amplitude of the low-pressure pattern. Additionally, this wake-induced excitation significantly alters the aerodynamic excitation, particularly for modes involving large displacements at the leading edge. A criterion originally used to evaluate the impact of separation bubbles on performance is applied to assess the existence of this excitation.
Zheng et al. (Sun,) studied this question.