| dc.description.abstract | High performance turbomachinery often experiences severe dynamic loads that produce large amplitude rotor motions. Well-engineered squeeze film dampers (SFDs) provide adequate damping to ameliorate rotor vibrations and to ensure system reliability. Open ends SFDs are prone to air ingestion during large amplitude rotor whirl motions and high excitation frequencies, all the while demanding of a significant flowrate, an undesirable operating feature. Piston ring (PR) end seals are commonly installed in SFDs in aircraft engines to amplify the available damping while reducing the demand of oil flowrate and also to avoid air ingestion.
This dissertation investigates experimentally the dynamic forced performance of a SFD with a short land length (L/D=0.2), nominal clearance 0.254 mm and lubricant supplied via three orifice feed holes (ϕ=2.5 mm). There are two configurations, one has its ends open to ambient while the other has sealed ends with PRs. The dynamic load tests are of three types (single frequency, sine-sweep frequency dynamic loads and impact loads).
Single frequency dynamic load tests reveal that the piston ring end seals effectively reduce leakage through the ends of the film land; thus the sealed SFD provides 11-13 times more damping coefficient and eleven times more added mass coefficients than those provided by an open ends SFD configuration. Further tests of two PR sealed ends SFDs (one with a seal flow conductance = 0.56 LPM/bar, and the other with = 0.89 LPM/bar) operated at a supply pressure Pin-1~0.69 barg, show that small differences on their damping and added mass coefficients are within the measurement uncertainty range. The second pair of piston rings (Cave-S2>Cave-S1 ) has a larger slit gap than the first pair, hence providing a lesser flow resistance. The effect of lubricant supply pressure on the sealed ends SFD force coefficients is also quantified experimentally by increasing the lubricant supply pressure by a factor of four (Pin-1~0.69 barg→Pin-2~2.76 barg). For the sealed ends SFD with Cave-S1 and Pin-2~2.76 barg, both the damping and added mass coefficients show a ~20% increase compared to those coefficients from the damper supplied with a low oil feed pressure (Pin-1~0.69 barg).
Further experiments with the sine-sweep frequency dynamic load tests aim to validate the SFD force coefficients identified from a single-frequency dynamic load. The estimated SFD damping and inertia force coefficients from a sine-sweep frequency load tests with a low time rate of change in sine-sweep excitation frequency α=6.5 Hz/s agree with the coefficients obtained from a single-frequency dynamic load over the same test conditions while substantially reducing the time of data collection.
Furthermore, single impact load tests are performed to quantify their effect on the response of an elastically supported open ends SFD and sealed ends SFD. Test system transient responses due to a single impact show the peak amplitude of motion (ZMAX) is proportional to the magnitude of applied load (FMAX). The identified system damping ratio (ξ) is proportional to the peak dynamic displacement as a linear system shows.
The dissertation discloses the full detail of the test dampers geometry and the experimental results which will provide a design reference to the practitioners. | en |
