Abstract
Most of the modern gas turbine engine designs requiring super critical operations will often have squeeze film dampers (SFDs) on the high pressure spool bearing as an inevitable feature. However, Squeeze Film Dampers are not very common for inter-shaft bearing applications and are still in the research and development stage. The current effort concentrates on static stiffness parametric studies based on newly conceptualized intershaft squeeze film damper (ISSFD) ring design suitable for space constrained intershaft bearing application of a typical two spool configured system. The work involves static stiffness evaluation of three and four grooves ISSFD rings by varying the groove angle/groove length/subtended angle of groove & hence the overlapping angle of grooves by conducting static tests on a dedicated static stiffness evaluation test rig designed and fabricated for the purpose. The pattern of circumferential variation of stiffness of each ring is studied and the results revealed a typical trend of decreasing stiffness in ISSFD ring with the increase in groove angle and hence the overlapping angle of grooves. The static stiffness parametric studies has resulted in developing an ideal profile of ISSFD ring having six grooves that exhibited axisymmetric pattern of circumferential variation of stiffness. When used in a space constrained intershaft bearing plane of a typical two spool gas turbine engine, the ideal ISSFD ring profile would exhibit the best damping performance. 
 Keywords: Inter Shaft Squeeze Film Damper (ISSFD), Gas Turbine Engine, Static stiffness, two spools, grooves.
Highlights
A squeeze film damper (SFD) is essentially a simple device consisting of an oil film interposed between the nonrotating outer race of a rolling element bearing and its housing
The screw rod is slowly rotated through hand wheel and thereby load is slowly applied in steps on the intershaft squeeze film damper (ISSFD) ring and corresponding deflection of groove/slot is noted down at every marking created at intervals of 15°on the ring
A mirror image of 0° to 45° circumferential variation of stiffness is seen from 45° to 90° and the maximum stiffness values are found at 0° and 90° positions of the groove
Summary
A squeeze film damper (SFD) is essentially a simple device consisting of an oil film interposed between the nonrotating outer race (sleeve) of a rolling element bearing and its housing. Most of the work that is reported in the past doesn’t look to be feasible from practical application point of view of a typical space constrained gas turbine engine setup and the unavailability of SFD design for an intershaft bearing plane still continues. When the circumferential variation of stiffness of ISSFD ring follows axisymmetric pattern, circumferential deformation of the ring will be axisymmetric. Under axisymmetric pattern of circumferential deformation of the ring, squeezing of oil film will have axisymmetric pattern and the damping effect created by such an ISSFD ring will be very effective. An ISSFD ring with axisymmetric pattern of circumferential variation of stiffness would provide effective damping as the absorption of kinetic energy of the moving surfaces would happen in an axisymmetric pattern. Static stiffness parametric studies is carried out with an intention to develop an ideal ISSFD ring profile that exhibits axisymmetric pattern of circumferential variation of stiffness
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