ROTOR DYNAMICS OF TURBOMACHINERY2. damper supports
Main functions of various DSs are:
- Reduction of a support stiffness and thus changing of the engine dynamic system. The natural frequencies are reduced, resonances are removed from the operating ranges.
- Absorbing of the vibrating system energy by transferring it into heat. This does not allow large vibration amplitudes, and thus large loads and stresses in the engine parts.
Main requirements to aviation engines DSs are the following:
- The support shall have a particular stiffness, which is determined by the engine Dynamics analysis. The analysis result is removing of the rotor resonances from the engine operating range.
The support shall have a particular damping to avoid large vibrations at various operation conditions, including extreme conditions.
The support shall permit sufficient radial displacements. The needed radial displacement is determined by a formulae:
,Here
k - support stiffness coefficient; m - rotor mass; n - vertical overload coefficient due to an airframe evolutions (for example, cargo planes have n = 2 to 2.5); g - gravitational acceleration; kd - dynamic amplifying coefficient for rotor vibrations in the support (kd = 4 to 6); e - eccentricity of the rotor unbalance, which is taken equal to maximal tolerance, including operating unbalancing. It is defined by permittable unbalance (me)d on the particular support:
. - To avoid great radial displacements and flexible elements overstressing the displacements are limited by special limitators which come to operation only at extreme non-design conditions.
- To avoid the rotor and stator non-axiality the datum surfaces of flexible elements are preliminary displaced as to equalize statical displacements due to the rotor weight.
- The dapmer design shall have specific features permitting to control its performances and to optimize them at the engine development.
- Stability of supports dynamical performances requires high accuracy of manufacturing of flexible elements, fitting surfaces, throttle holes etc. For this purpose are used high classes of accuracy, selective assemblying and other specific technologies.
