Mechanism analysis of frequency lock-in vibration in turbine cascades under transonic buffet flow conditions

The transonic flow is prevalent in the aerospace field. It is characterized by a complex flow mechanism and can induce intricate aeroelastic phenomena, resulting in substantial structural vibrations or even fractures. This paper investigates the aeroelastic characteristics of a cascade buffet based on a data-driven unsteady aerodynamic model. Using the computational fluid dynamics/computational structural dynamics method, the researchers revealed the occurrence of flutter under both subcritical and supercritical flow conditions. An aeroelastic analysis method was employed to analyze the mechanism of this flutter phenomenon. To analyze the aeroelastic characteristics of the cascade, an unsteady aerodynamic model was established under subcritical flow conditions. Coupling the aerodynamic model with the structural motion equations, an aeroelastic model was developed. An analysis of the eigenvalue trajectories of the aeroelastic model revealed structural mode branch instability. The structure near the buffet onset boundary exhibits two distinct instability modes. The instability of the 1 nodal diameter mode in the low-frequency region arises from the coupling between the structural mode and the zero-frequency flow mode, leading to an unstable phenomenon similar to laminar separation flutter, while the instability near the buffet flow frequency region is due to the mutual exclusivity between the structural mode and the buffet fluid mode.