In the previous report (ref. 2), it was cleared that the unbalance vibration of single spool turbo-jet engines and vibration damping effect of the squeeze film damper bearing can be estimated accurately enough for design purpose, by the theoretical calculation.
Following these results, calculations of unbalance vibration of typical 2 models of 2 spool fan-jet engine were made, considering different rotational speeds of rotors.
The results of the calculation show that-
(1) Medium to large size 2 spool fan-jet engines have many resonance frequencies in their speed ranges, and at some speeds and at some positions, amplitude of vibration will exceed critical value, in the case of no damper bearing.
(2) In the most cases, amplitude of vibration at the critical speeds can be suppressed to safe value, by using one or two damper bearing (s) at the adequate position (s).
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