Experimental Rotordynamic Coefficient Results for a Load-on-Pad Flexible-Pivot Tilting-Pad Bearing With Comparisons to Predictions From Bulk-Flow and Reynolds Equation Models

Experimental dynamic-stiffness-coefficient results are presented for a high-speed, lightly loaded, load-on-pad, flexible-pivot tilting-pad bearing. Results show that the real part of the direct dynamic-stiffness coefficients are quadratic functions of the excitation frequency. This frequency dependency is modeled well by an added-mass coefficient, and the resultant [M], [K], and [C] matrix model is frequency-independent versus a conventional [K] and [C] model that is frequency dependent. The dynamics introduced by the additional pad degrees of freedom (including pad inertia and web moment stiffness) and the effects of fluid inertia in the lubricant film account for part of this frequency dependency. Experimental results are compared to numerical predictions from models based on: (i) the Reynolds equation, and (ii) a Navier-Stokes (NS) equations bulk-flow model that retains the temporal and convective fluid inertia terms. The NS bulk-flow model results correlate better with experimental dynamic stiffness results, including added-mass terms. Both models underestimate the measured added-mass coefficients for the full excitation range; however, they do an adequate job for excitation frequencies up to synchronous frequency. The frequency dependency predicted by using a [K] and [C] model can be removed by adding a mass matrix to the reaction-force model with either a Reynolds equation or a bulk-flow NS model, with a very considerable speed up in calculation of damped eigenvalues for rotor-bearing systems.