2.1 hydrodynamic damper supports
Hydrodynamic damper supports can be located in compressor and/or turbine areas (Fig. 1).
Fig.1 Compressor support with Hydrodynamic damper
Damping function is performed by a 0.1 to 0.3 mm thick oil film between the bearing outer ring and the casing. The oil film thickness determines the support radial displacement. The oil is high pressure supplied into the spacing between the bearing outer ring and the casing from an annual groove. The damper is sealed by two piston rings which reduce oil consumption and permit the rotor precession within the spacing.
At engine operating in the film there is produced a hydraulic force, so the oil film can transmit radial loads to the casing. On the other side the hydraulic force resists to the rotor precession in the support, i.e. a resisting or damping force is produced. A specific feature of such supports is that they are not to transmit axial loads when installed with roller-bearings or transmit small axial loads when installed with thrust ball-bearings in terms of not to meet self-stopping effect.
The oil film in the damper is highly loaded which is followed by significant production of heat. It has an influence on the oil viscosity at different engine operating conditions. So to permit the support stability the sealing rings are to allow nesessary oil massflow.
The oil massflow through the support depends on supplying
pressure, oil temperature and main damper dimensions and fittings.
Usually the massflow in different engines is within 10 to 100 kg/hr. Dampers without seals need 2 to 3 times greater oil consumption and are seldom used in aviation engines but are widely used in marine application engines.
The temperature state and oil consumption are investigated
Support dynamic performances (stiffness k and damping c ) are nonlinear and depend on rotor location in the damper clearance (Fig.2).
Fig. 2 Example of damper dynamic characteristics
- eccentricity ratio; - eccentricity between journal centre and housing centre; - radial clearance (housing radius - journal radius).
These supports advantages are small size, reliability, high damping and bearing ability, availability of mathematical models. The main shortcoming is nonlinear dynamic performances - the support operates from some speed of rotor rotation, without rotation there is no rotor centering, so the blades tip clearance is to be greater than the damper clearance.
Are known hydrodynamic supports with two or more oil films separated by free rings. Such supports have good bearing ability and damping and can be used for reduction of high dynamic loads at extreme situations [ 6 ].