Analytical and Experimental Investigation of Squeeze-Film Dampers Executing Circular Orbits

We have referred here the first results obtained in the course of an experimental research intended to examine oil film pressure of a squeeze film damper (with inertialess lubricant) executing circular orbits. An analytical expression for pressure arising into the gap was obtained before, for the short bearing SFD, in the general case of offset circular orbits. The expression obtained has permitted, in a simple way, the examination of the influence of the offset on pressure. Two approximated expressions for pressure (the one for pressure as a function of time at a fixed measuring section, the other for pressure along the circumference of the bearing at a given time), corresponding to centered orbits, were compared with the exact ones. We observed that the limits within which the nondimensional offset can be considered negligible, change according to comparisons between circumferential pressure diagrams or between pressure diagrams as functions of time. In the second case they are much wider. The experimental results concerned offset orbits with nominal radius r = 0.5C and offset δ < 0.1. Good accordance between theoretical and experimental pressure trends has been found, as concerns the positive part of dynamic pressure. As concerns the negative part of dynamic pressure, tests have shown that cavitation takes place for a more or less wide length, depending on feeding groove pressure, other conditions being equal. Complete effective pressure diagram coinciding with the theoretical one has been found for particular feeding conditions. Oil film tensile stresses have been frequently detected with both complete and incomplete diagrams owing to cavitation. Maximum measured tensile stress was about 220 kN/m2. It was finally found that theoretical and experimental trends are coincident only if the SFD is not starved. Analytical expression for pressure in the long bearing SFD executing offset circular orbits is referred in the appendix.