Dynamic Characteristics of Air Cycle Machine Rotor System

Table 2

Applying condition for unbalanced exciting force.

Conditions	Turbine	Compressor	Unbalanced exciting force	Bearing stiffness
1	F0e^jΩt	F0e^jΩt	Same amplitude and same phase	Isotropy; Anisotropy
2	F0e^jΩt	F0e^j(Ωt−90°)	Same amplitude and different phase	Isotropy; Anisotropy
3	F0e^jΩt	F1e^jΩt	Different amplitude and same phase	Isotropy; Anisotropy
4	F0e^jΩt	F1e^(Ωt−90°)	Different amplitude and different phase	Isotropy; Anisotropy

Annotation. Unbalanced exciting force: different phase means the compressor falls 90° behind the turbine. Different amplitude means F₁ = 1/2 F₀. Bearing stiffness anisotropy: the bearing principal stiffness in the horizontal direction is equal to 1/2 of the bearing principal stiffness in the vertical direction.