HIGHER HARMONIC OSCILLATIONS IN A NONCONTACTING FMR MECHANICAL FACE SEAL TEST RIG

In order to investigate experimentally the dynamic behavior of a nonco ntacting flexibly mounted rotor (FMR) mechanical face seal a test rig was designed and built. Test results showed that the FMR seal was vuln erable to higher harmonic oscillations with frequencies that are integ er multiples of the shaft speed. Because system nonlinearities can cau se higher harmonic oscillations, the dynamic moments ''ting on the rot or are derived to include the effects of imbalance and axial offset of the rotor. The analysis reveals that the nonlinear terms involved are of second order and generally can be neglected. Investigation is then directed to analyze the possibility of rubbing contact between the ro tor and the stator. Rubbing contact can occur as a result of a high re lative angular misalignment between the rotor and the stator. A contac t kinematics model is proposed and a Fourier series analysis is perfor med on the resulting rotor response. The analysis shows that the propo sed response contains higher harmonics. Fourier series expansion and n umerical filtering of a sampled rotor response from the test rig yield resembling signals which contain higher harmonics. This suggests that rubbing contact is the source of higher harmonic oscillations. Design modification to the rotor flexible support system resulted in a virtu al elimination of higher harmonic oscillations.