ROTOR DYNAMICS OF TURBOMACHINERY3.3 Design and analysis of a support with a Hydrodynamic damper and flexible element
3.3.1 Topics.
In a support furnished with a Hydrodynamic Damper and flexible Element (HDFE) the oil film has low bearing ability at small eccentricities, in other words the FE stiffness is much higher than the film stiffness. It permits to have constant support stiffness and to obtain high damping in a not cavitated damper.
Oil film stiffness and damping can be calculated equally to a HD without an EE.
Below are given some specific features of a HDFE:
- If the amplitude of the journal orbit is very large the oil film hydrodynamic stiffness can be greater than the FE stiffness.
- If the amplitude of the journal orbit is about half of the clearance the FE centers the damper and reduces dynamic transmissibility.
- A single-directed dynamic loading increases the dynamic transmissibility coefficient and causes a subharmonic movement due to nonlinear effects.
- At some level of unbalances the vibration amplitude can change rapidly ("jump" - effect). At speed increase the amplitude rapidly increases, at speed reduction the amplitude can rapidly decrease. This effect is concerned to a rapid change of the dynamic transmissibility coefficient due to nonlinear damper properties.
- A HDFE design improvement can cause increase of transmitted forces even compared to stiff supports. It can occur in a range of speeds W < 1.4, which should be avoided by support design.
