The Effect of Air Ingestion on the Dynamic Characteristics of SFD Oil Film

The effect of air ingestion on the dynamic characteristics of oil film of Squeeze Film Damper (SFD) is crucial important to improve the vibration and noise reduction performance of aero-engines. In order to solve the problem of unclear influence of air ingestion on the dynamic characteristics of oil film of Squeeze Film Damper, a study was carried out. Modeling the fluid domain of squeeze film damper. The presence or absence of air ingestion was considered in two cases. The influence of air ingestion on the dynamic characteristics of the oil film was analyzed under different structural and operating parameters such as whirl frequency, static eccentricity, whirl radius, gap ratio, oil film width, oil supply pressure and oil viscosity. The mechanism of air ingestion on the dynamic properties of oil film was revealed. The results showed that the air ingestion phenomenon occurs at the exit boundary when the equipment was in operation. When the dynamic pressure lubrication effect of fluid increased as a result of changing structural or operating parameters, the degree of air ingestion is increased and its distribution becomes more uniform along the circumference. Air ingestion caused a significant reduction in the maximum pressure value, but has little effect on the range of the positive pressure zone. Meanwhile, air ingestion led to a substantial reduction in the range of the negative pressure zone of the oil film, resulting in a considerable decrement in the cavitation effect of the oil film, which in turn affected the dynamic characteristics of the oil film. Air ingestion reduced the effective oil film coverage area, increased the cavitation ratio, significantly reduced the fluid viscosity, reduced the dynamic pressure lubrication effect, and had a more significant effect on the dynamic properties of the oil film compared to the cavitation effect. Air ingestion produced a significant inhibitory effect on the dynamic characteristics of the Squeeze Film Damper oil film, which is manifested in the overall stability improvement of the damping and stiffness, with a significant reduction of the specific values and the alleviation of the nonlinear characteristics. When air was ingested, increasing the aspect ratio, oil supply pressure, and decreasing the whirl frequency can effectively enhance the oil film damping and stiffness. Changing the static eccentricity, whirl radius, clearance ratio, and oil viscosity had a small effect on the dynamic characteristics of the oil film. When the static eccentricity was constant, the degree of air ingestion varied slightly from one typical moment to another. It caused the damping and stiffness to vary, while the trend with the parameters was generally identical. The research results could provide theoretical basis and important reference for the subsequent in-depth study and optimized design of the dynamic characteristics of Squeeze Film Damper oil film without end seal and vibration characteristics of a rotor system fitted with an unsealed Squeeze Film Damper.