Vibration Feature Identification and Mechanism Analysis of Aero-Engine Test Stand Based on Integrated Finite Element Modeling and Bispectral Analysis

Aero-engine test stand systems are characterized by complex structural configurations, a wide excitation frequency range, and vibration signals containing multiple harmonic components. Under multi-harmonic excitation, nonlinear vibration responses may exhibit complex frequency coupling, making it difficult to distinguish linear resonance from nonlinear coupling effects. To address this issue, a vibration feature identification method integrating finite element modeling and bispectral analysis is proposed. Finite element analysis is first employed to determine the natural frequencies of the test stand structure, while bispectral analysis is used to characterize the frequency coupling relationships associated with nonlinear vibration and to investigate its potential underlying mechanisms. Analysis of the test stand system and measured vibration data demonstrates that the dominant vibration peaks during the startup stage agree well with the numerically predicted modal frequencies, indicating that the vibration response is primarily governed by structural resonance. During the steady-state stage, bispectral analysis reveals nonlinear frequency coupling among the vibration components. In particular, a coupled difference frequency of 155 Hz falls within the near-resonance band of the test stand and is consequently reamplified by the structure. This process indicates a closed-loop mechanism characterized by structural resonance, nonlinear coupling, and structural reamplification. The proposed method provides an effective means of distinguishing linear and nonlinear vibration components and offers a quantitative basis for interpreting the vibration mechanisms of aero-engine test stand systems.