Abstract
A significant advancement in the dynamic spin rig (DSR), i.e., the five-axis, three-magnetic-bearing DSR, is used to perform vibration tests of turbomachinery blades and components under rotating and non-rotating conditions in a vacuum. The rig has three magnetic bearings as its critical components: two heteropolar radial active magnetic bearings and a magnetic thrust bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feedforward control feature, which enables the excitation of various modes of vibration in the bladed disk test articles. The theoretical, mechanical, electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated, rotating and non-rotating, unbladed rotor and a fully levitated, rotating and non-rotating, bladed rotor in which a pair of blades were arranged 180° apart from each other. These tests include the “bounce” mode excitation of the rotor in which the rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from the plot of acceleration versus frequency. For non-rotating blades, a blade-tip excitation amplitude of approximately 100 g A−1 was achieved at the first-bending critical (≈144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip displacement of 1.778×10−3m (70 mils) was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 90° relative to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm.
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Abbreviations
- A :
-
cross section (m2)
- B :
-
magnetic flux density (T)
- c :
-
constant defined in eq (A9)
- F :
-
net controlling force on rotor (N)
- f :
-
force on rotor due to one pole (N)
- g :
-
acceleration due to gravity (9.8 m s−2)
- H :
-
magnetic field (A m−1)
- i :
-
current in coil (A)
- K :
-
control gain
- K:
-
stiffness
- k eq :
-
rigid rotor equivalent spring constant
- l fe :
-
mean length of magnetic displacement (m)
- m eq :
-
rigid rotor equivalent lumped mass (kg)
- n :
-
number of turns in coil
- s :
-
air gap spacing (m)
- \(\dot s_{de} \) :
-
linear velocity of shaft (m s−1)
- \(\ddot s_{de} \) :
-
linear acceleration of shaft (m s−2)
- V :
-
volume (m3)
- W :
-
magnetic energy (J)
- Φ:
-
magnetic flux (Wb)
- μ:
-
permeability (T m A−1)
- μ0 :
-
permeability of free space (T m A−1)
- ω:
-
excitation frequency (rad s−1)
- A a :
-
through air gap cross-section
- A fe :
-
through iron cross-section
- a :
-
air gap between stator and rotor
- b :
-
bias
- c :
-
control
- d :
-
derivative
- de :
-
deviation from nominal gap distance between stator and rotor
- eq :
-
equivalent
- ex :
-
excitation
- fe :
-
iron
- i :
-
current
- l :
-
linearized
- p :
-
proportional
- r :
-
relative
- s :
-
position
- O:
-
nominal
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Morrison, C.R., Provenza, A., Kurkov, A. et al. Fully suspended, five-axis, three-magnetic-bearing dynamic spin rig with forced excitation. Experimental Mechanics 45, 226–237 (2005). https://doi.org/10.1007/BF02427946
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DOI: https://doi.org/10.1007/BF02427946