For high-precision mechanical systems such as gas-turbine engines, which operate under extreme conditions, it is particularly important to accurately predict the behavior of the mainshaft rolling bearings. This prediction includes, among others, the load distribution, stiffness and power dissipation. Although shaft speeds tend to increase, rings and shaft walls are becoming thinner due to size and weight constraints. Thus, bearing behavior is no longer independent of the housing and ring stiffness. Furthermore, since forty years, the use of squeeze film damper is largely widespread in gas-turbine engines to significantly reduce the vibratory levels. Due to the flexibility of the ring providing the interface between the roller bearing and the fluid film, it appears an elastic coupling which modifies the behavior of the bearing-squeeze film damper system. This paper presents first a squeeze film damper model with a flexible inner ring (i.e. outer ring of the roller bearing). An analytical stop model is introduced to reproduce the interference between the inner ring of the squeeze film damper and its housing. In a second part, an elastic coupling between the presented squeeze film damper model and an existing roller bearing model is proposed. Finally, the results presented show that this coupling has a first order influence on the behavior of the bearing-squeeze film damper system. It is also shown that the coupling between a roller bearing and a squeeze film damper when linked by a flexible ring introduces a dissymmetry of the load distribution with respect to the applied load direction. Moreover, in certain cases, the position of the bearing in its housing can reach eccentricities larger than the radial clearance of the squeeze film damper.
Generalized High Speed Simulation of Gas Turbine Engines
