Optimum Design of Intershaft Squeeze Film Damper (ISSFD) Ring for Vibration Attenuation

Squeeze film dampers (SFDs) have become an inevitable feature in aircraft gas turbines which usually get introduced on one of the bearings supporting the HP spool. There are no practical attempts being made to introduce external damping in the other bearing supporting the HP spool, which usually is an intershaft bearing. This work essentially attempts to optimize the design of Intershaft Squeeze Film Damper (ISSFD) ring that could be introduced in the intershaft bearing plane satisfying the space constraint to attenuate vibration. The work involves the fabrication and testing of ISSFD rings for the optimum design by evaluating their static stiffness and damping potential on specially built instrumented test facilities. The static stiffness value of ISSFD rings is evaluated using a static test rig, and the damping potential of rings is evaluated on a single spool dynamic test rig in terms of vibration attenuation capability and also by quantifying the damping factor. ISSFD rings each having three, four and six grooves were tested, and the percentage reduction of vibration amplitude normalized with bearing support stiffness was evaluated. The introduction of oil in the grooves of ISSFD rings resulted in increased bearing plane stiffness and damping thus resulting in increased critical speed and vibration attenuation. Six grooved rings demonstrated relatively a high level of performance defined in terms of vibration reduction levels. Critical speed analysis is carried out on the FE model of the rotor bearing system and the critical speed values obtained correlate well with experimental values.