While in operation, aircraft engines may be subjected to various severe mechanical events such as bird ingestion, blade separation, ice accretion, shaft unbalance, compressor stall or rotor-stator interaction. During the development of a new engine application, such phenomena are simulated in test cells in order to make sure that the engine will still operate safely. During such tests, accelerometers and strain gages are mounted on the engine cases and near the shaft bearings in order to measure loads and vibrations and in order to understand the engine behaviour. The engine dynamic behaviour during those phenomena may be fleeting or sustained, cyclic or asynchronous, transient or stationary. Usual analysis are performed in various domains such as time, frequencies and orders of a rotating shaft speed, depending on the nature of the vibration behaviour.

This paper describes a new kind of vibrations representation that considerably facilitate the interpretation of fleeting or sustained events when both time and phase location of a shaft are meaningful. In a first section of the paper, the representation is described with a simple lumped-mass model of a rotating shaft operating with variable angular speed. In a second section, the representation is applied on a real aircraft engine during tests with various engine behaviours. The last section presents a simulation of those different behaviours with a simple model.