Abstract
Owing to its excellent vibration isolation capability, the squeeze
film damper is finding increasing use in industry, particularly in
the gas turbine industry. Design information for squeeze film
damper supported flexible rotors has been scarce and has been
restricted mainly to small journal orbit eccentricity, and
consequently to small unbalance loading. However, unbalance loading
can increase in service, resulting in highly undesirable operation
modes. This thesis analyses theoretically and experimentally the
effect of the relevant system parameters on the possibility of such
undesirable operation modes, on unbalance force transmissibilities,
on rotor excursion amplitudes and on the orbit stability of squeeze
film damper supported flexible rotors, with a view to aid the design
of such rotor bearing systems. Assuming Reynolds equation with
constant lubricant properties, the short bearing approximation and
synchronous symmetric motions, the equations of motion are solved
numerically. Rotor excursion amplitude and transmissibility data
are presented for a wide range of operating conditions, showing the
effect of the system parameters on the responses. It is shown that
pressurization of the oil supply is conducive to smooth passage
through the first pin-pin critical speed of the rotor. The system
stability is investigated for small perturbations from the
equilibrium solution (using Routh's criterion) and stability maps
are superimposed on the journal eccentricity frequency response
plots). Pressurization is shown to stabilize the rotor bearing
system and supply pressure data are presented, showing the minimum
pressure required to suppress the undesirable operation mode and to
ensure stable operation. A theoretical model is developed for
optimal fine tuned system design. Optimal support data and the
system responses are presented on a single chart for a wide variety
of rotors operating under the second bending critical speed. The
design and commissioning of the experimental rig and the subsequent
experimental investigation to verify the theoretical findings are
described in detail. Very good agreement is obtained between
theoretical predictions and experimental results. It is concluded
that the theoretical model and predictions are valid.