Hydrodynamic journal bearings supporting high mass rotating machinery are subjected to
low rotational speeds during start-up or idling phases. These working conditions need a
hydrostatic pressure contribution to ensure a correct load capacity when the hydrodynamic
pressure is not established yet. This is possible by means of hydrostatic lift pockets.
These pockets avoid mechanical damages via sufficient film thickness from start-up to
hydrodynamic working conditions. In a first part, it is showed how an existing isothermal
3D hydrodynamic numerical modelling of tilting pad bearing has been adapted to take into
account the lift pocket impact on static bearing performance. This approach is only valid
for low rotational speeds, when inertia step pressure effects (rises or drops) at the
film-pocket edge can be neglected compared to the total bearing pressure pattern. Then,
numerical simulations have been performed, from 1 to 200 rpm with pockets and from 75 to
200 rpm without pockets. The results have been compared and discussed in terms of pressure
fields and bearing static performance such minimum film thickness, friction torque or
rotor center position. Therefore, the interest of such lift pockets has been highlighted.
Finally, calculations with and without pockets have been carried out in case of a strong
bearing misalignment. As a result, the benefits of the lift pockets in this configuration
are also significant in terms of static performance.