Measurements of unbalance response in a squeeze film damper test rotor-kit

Abstract

Measurements of the unbalance response in a squeeze film damper (SFD) rotorkit are presented. The rotor-SFD test apparatus and instrumentation are fully described. Results from the measurements of the system unbalance response are presented for three cases: centered journal, offcentered journal at 30% and 60% of the radial clearance. Different masses of unbalance are used for each case . All the experiments were performed at room temperature and at an oil inlet pressure of 6.9 kPa. The cascade plots of the unbalance response show no trace of asynchronous vibrations. However, the last case studied Ooumal offcentered at 60% of the radial clearance) showed a supersynchronous vibration tracking the unbalance response at about twice the rotational speed. A commercial rotordynamics code (PUP) was used to extract the damping coefficients at the damper support by a trial and error procedure using the criteria to match the model with the experimental results. The pressure distribution was experimentally measured at the top of the SFD and no oil cavitation was detected from the tests. However, air entrainment was clearly observed while passing through the system resonant speed. Theoretical pressure distribution plots from a "short bearing" model did not compare well with the experimental data. The rotor deflected shapes of the centered unbalance response were calculated using the rotordynamic model to predict the amplitude of vibrations at the SFD location and from these results theoretical damping coefficients were evaluated with equations for the centered and non-cavitated SFD. Damping coefficients for the offcentered cases were estimated (in the vertical direction) from transfer function tests and also were calculated using a computer code with the assumption of no cavitation in the damper. The comparison of these last results was extremely good.