Dynamic characterisation of a multi stage axial compressor test rig rotor system

Dynamic properties of support structures play major role in controlling the vibration amplitudes of test rigs involved in the development of gas turbine engines rotors. These rotors often operate in the supercritical speed regimes, which necessitates the prediction of their dynamic characteristics more accurately. In the present study, numerical simulation of dynamic characteristics of a multi-stage compressor test rig rotor supported on rolling element bearings and a Squeeze Film Damper (SFD) has been carried out.

A methodology using numerical methods and analytical relations, was developed to evaluate the stiffness of the bearing support structur. Bearing support structure stiffness values were evaluated using finite element method, employing the developed methodology. Finite element analysis of rotordynamics was carried out, taking into account the non-linear properties of both rolling element bearings and SFD. A sensitivity analysis was carried out on SFD parameters to understand the behaviour of the system under different geometry and operating conditions.

Comparison of results obtained for the present rotor system showed that the non-linearities in the SFD play major role in the dynamics of the system, compared to the non-linearity in the bearings. Sensitivity studies carried out for the range of SFD parameters revealed that the SFD clearance, viscosity and unbalance are important parameters that determine the maximum amplitude of response and also force transmitted to bearings, whereas the supply pressure was one of the least affecting parameters.