The most effective method for the vibrations mitigation and reduction of the dynamic stress in engine components is the use of supports with hydrodynamic dampers. They are widely used in engines: from the large ones for transport and civil aviation (D-36, SaM146, PD-14), military aircraft (RD-33, AL-31F, AL-41F) to small ones for commercial aviation and UAV.
Theoretical background
DYNAMICS R4 uses both analytical models based on the 1D Reynolds equation solutions and the numerical models based on 2D Reynolds equations. Analytical and numerical damper models when applied within their basic assumptions show adequate results. The analytical models require much less computer calculations. Thus, the calculation with a one-dimensional damper model (analytical solution) requires about two orders less calculation time than the two-dimensional damper model, or the numerical solution.
Features of the hydrodynamic damper operation
- If the amplitude of the rotor precession orbit in the damper is very large, then the oil film stiffness can be much higher than the flexible element stiffness.
- If the precession orbit amplitude is approximately half of the gap, then the spring element centers the damper and reduces the dynamic amplification factor.
- Unidirectional dynamic loading increases the dynamic Amplification Factor and causes subharmonic motion due to non-linear effects.
- In a sqeeze film damper with centering spring, there may be a certain level of imbalances, at which the vibration amplitude can change abruptly from low to large (“jump” phenomenon). A speed reduction may result in an abrupt amplitude increase. This phenomenon is associated with an almost step change in the dynamic Amplification Factor due to the non-linear properties of the damper.
- Including of a hydrodynamic damper into the rotor bearing support can increase the transmitted dynamic force, even compared to rigid bearings, if the damper operates in the operating frequency range, where the frequency ratio ω/ωc < 1.4. This area must be avoided in the damper design.