2.2 supports with hydrodynamic damper and flexible element
On the contrary to the previous supports type these supports can transmit significant axial loads from a thrust ball-bearing to its casing. They can be located in a compressor or turbine area (Fig. 3).
Fig. 3 A damper support with a flexible element.
The flexible element is a metal hollow cylinder having axial slots cut along circumference to permit flexibility and resiliency (“squirrel - cage”). One end the cylinder is firmly affixed to a casing, the other end firmly affixed to end of bearing retainer. Between the retainer outer surface and the casing there is an annual clearance d, Fig.12 .
The bearing radial load produces bending displacements in the bars of damper flexible element. Every bar operates as a stiffly restrained by its ends beam, one of the beam ends can move under the load. All the beams have equal displacements limited by the radial clearance d. The bearing axe moves parallel to itself so the bearing misalignments and local overloadings are excluded. Such supports are used both with annular and in angular contact bearings.
For the bars to have equal stiffness in all the bending directions they are to have circular cross-section. There are some designs where the circular bars are brazed or thread inserted into flanges. Some designs have bars of rectangular cross-section.
Damping function is performed by a 0.1 to 0.3 mm thick oil film. The oil film thickness determines the support radial displacement. The oil is high pressure supplied into the spacing from a circular groove. Damping performances depend on thickness and length of the oil film.
The damper dimensions are approximately determined by calculation and tuned experimentally.
A total support stiffness consists of a flexible element stiffness ky and oil film stiffness kg
Damper supports with flexible elements are designed in terms of having the oil film stiffness at least one order smaller than the flexible element stiffness. If so, the support dynamic performance is practically constant (Fig. 4).
This type of supports advantages are the following: constant stiffness performances within the whole operating range; possibility to transmit high axial loads; reliability; high damping; a rotor centering without rotation; there are available calculating models.
The main shortcomings are large sizes and mass and nonlinear
Fig 4 Stiffness and damping of a damper support with a