On the Influence of the Lubricant Feed Orifice Size and End Plate Seals’ Clearance on the Static and Dynamic Performance of Integral Squeeze Film Dampers

In rotating machinery squeeze film dampers (SFDs) reduce rotor synchronous response amplitude motions, provide structural isolation and enhance rotordynamic stability. Compared to conventional squirrel cage supported SFDs, integral squeeze film dampers (ISFDs) are more compact and require a shorter axial span. This paper presents predictions of pressure profile, lubricant flow rate and dynamic force coefficients of a four pads ISFD configured with distinct inlet orifices (d0 – 3 d0) and ends’ seal clearances (b1 - 3b1, b1 = 1/3 c). The dimensions of the inlet orifice (d0) and end seal clearance (b1) are based on an ISFD used in an industrial supercritical CO2 expander. Thin S-shape beams acting as springs divide the annular clearance into several individual fluid domains. The analysis quantifies the effect of the lubricant feed holes’ size and the end seals’ clearance on the static and dynamic forced performance of an ISFD for a typical compressor application. An increase in diameter for the inlet orifice, from d0 to 2d0, increases significantly the fluid film pressure in the all pads, delaying the whirl speed when vapor cavitation occurs. However, with a nominal clearance b1 = 0.191 mm, the damping and added inertia coefficients reduces by almost 1/3 as the inlet orifice diameter increases from d0 to 2d0. Although the damping and inertia coefficients of the ISFD are more sensitive to the end seal clearance than to the diameter of the inlet orifice, an increase in the size of the inlet orifice does weaken the relationship “damping ~ 1/clearance3”. In addition, predictions for the ISFD operating with an air in oil mixture shows that the damping and added inertia coefficients drop almost linearly as the inlet gas volume fraction (GVF) increases from 0.0 (all liquid) to 0.2.