3. Unsteady flow aspect

This aspect is of prime importance in turbomachinery. Apart from the case of a transient regime and distortion at the engine inlet, the vibratory behavior of the blades and the interaction between the fixed and moving impellers generate highly unsteady phenomena. Only the fan of a jet engine with a high bypass ratio can be considered stationary, provided the rotating frame of reference is used and the regime is established and free of distortion and aeroelastic phenomena. It should be emphasized that unsteady rotor-stator interaction is not yet explicitly taken into account in design methods; it is the experience and know-how of the designer who, through the application of rules of thumb, can avoid harmful effects.

However, if we want to take this rotor-stator interaction into account, we can make the following remarks:

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