| dc.description.abstract | Analysis of tilting pad journal bearings (TPJBs) has reached great complexity as 3D computational fluid dynamics models are coupled to finite element structural models for the pads, journal and bearing housing and account for fluid-solid interactions. The aim is to reach great levels of confidence (accuracy) in prediction of bearing performance without resorting to (expensive and time consuming) testing.
The thesis includes a thermo-elasto-hydrodynamic (TEHD) model that accounts for the pads structure mechanical deformation and includes pivot elastic displacements, both due to pressure and temperature changes. Note that in operation with a high shaft speed and/or under a heavy load, pad surface deformations due to both hydrodynamic pressure and thermally induced strains change the pad curvature and could increase its machined preload. These surface deformations affect the operating film thickness, thus influencing the bearing performance.
A theoretical analysis along with physically sound assumptions derives a simple equation for prediction of the thermally induced deformation as a function of the temperature difference between the inner and back surfaces, both circumferentially averaged. The simple equation delivers results in agreement with a FE structure model for a number of typical bearing pads.
This thesis also introduces a model for the mixing of flow and thermal energy at a feeding groove and sets the temperature of the lubricant entering a pad leading edge. Accurate knowledge of this temperature (and inlet oil viscosity) and the flow rate entering a pad largely determine the temperature rise along the pad lubricated surface as well as the shear drag power loss, and ultimately the load capacity.
The archival literature reveal the benefits and shortcomings of a commonly used hot oil carry over thermal mixing model. The novel thermal mixing model acts to deliver improved temperature predictions in conditions that limit the conventional model applications. An important modification is the ability to impose the actual supply flow, specifically when the bearing is operating in an over-flooded or reduced flow condition. In addition, the flow balance in the new model accounts for the groove side leakage flow (discharging out of the bearing) and the churning (recirculating) oil in the grooves. An empirical groove efficiency parameter regulates the temperature of above-mentioned flows in an effort to represent direct and conventional lubricant feeding arrangements as well as end-seal configurations.
Predicted static and dynamic force performance of two TPJBs are compared against test data in Refs. [1–5]. The performance parameters include journal eccentricity, pad surface temperature rise, flow rates in a feeding groove, fluid film thickness, hydrodynamic film pressure, bearing complex dynamic stiffnesses, as well as bearing (synchronous) stiffnesses, damping, and virtual mass coefficients. Performance predictions with and without including the thermally induced deformation of the pads, and using either the novel or the conventional thermal mixing models, are shown to demonstrate the improvement. | en |
