On the Performance of Tilting Pad Bearings: A Novel Model for Lubricant Mixing at Oil Feed Ports with Improved Estimation of Pads’ Inlet Temperature and Its Validation Against Experimental Data
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Energy efficient operation of fluid film bearings demands savings in delivery flow while also managing to reduce fluid film and pad temperatures. To achieve this goal, tilting pad journal bearings (TPJBs) implement a variety of oil feed arrangements (LEG, spray bars, etc.), use pads with highly conductive material and engineered back surface, and also end seals to keep (churning) lubricant within the bearing housing. Often, to evidence the savings, operators supply bearings with a fraction of the flow predicted by an analysis, independently of the system operating speed and likely (dynamic) load condition. The lecture briefs on an analysis of TPJBs that includes pivot flexibility and pad surface deformation due to hydrodynamic film pressure and pad crowning due to thermal effects. The work introduces a novel model for the mixing of flow and thermal energy at a lubricant feed port, which sets the temperature of the lubricant entering a pad leading edge. Precise estimation 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 bearing load capacity. Over decades, conventional modeling of TPJBs implements a hot oil carry coefficient to estimate thermal mixing at a feed groove. This model requires an empirical constant that is a function of the operating conditions (speed and load) and is apparently the same for all pads in a bearing. The present thermal mixing model delivers improved temperature predictions in conditions that limit the conventional model. An important addition is the ability to impose the actual lubricant supply flow, specifically when the bearing is ? Work conducted as a graduate research assistant at Texas A&M Turbomachinery Laboratory. ON THE PERFORMANCE OF TILTING PAD BEARINGS: A NOVEL MODEL FOR LUBRICANT MIXING AT OIL FEED PORTS WITH IMPROVED ESTIMATION OF PADS’ INLET TEMPERATURE AND ITS VALIDATION AGAINST EXPERIMENTAL DATA Luis San Andrés Mast-Childs Chair Professor Mechanical Engineering Department Texas A&M University College Station, TX, USA Lsanandres@tamu.edu Behzad Abdollahi Mechanical Engineer LobePro Rotary Pumps Brunswick, GA, USA Behzad.Abdollahi90@gmail.com 2 Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station operating in either an over-flooded or a 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 a groove or feed port. An empirical groove efficiency parameter regulates the temperature of the above-mentioned flows to represent conventional and direct (LEG, spray bars) lubricant feeding arrangements as well as end-sealed (flooded) or evacuated bearing configurations. Predicted static and dynamic performance for two TPJBs are compared against two sets of published test data in Refs. [1-5]. One is a large 5-pad bearing (500 mm ID) with end seals and supplied with a flowrate as low as 50% of the nominal (predicted) condition. The rotor speed is 3 kRPM (79 m/s surface speed) and the maximum specific load equals 25 bar. The other bearing is a 4-pad (102 mm ID) operating with a fixed flow rate, invariant as the speed increases to 16 kRPM (85 m/s) with an applied load increasing from 7 bar to 29 bar. Comparisons with the first bearing include the film thickness, pressure and temperature fields around the bearing circumference, as well as journal static eccentricity and synchronous speed reduced force coefficients. The second bearing incorporates a variety of oil feed arrangements and offers dynamic force coefficients over a range of excitation frequencies. Bearing performance predictions using either the novel model or the conventional thermal mixing model, when compared against the test data, demonstrate the improvement. The lecture concludes delivering recommendations for the feed port efficiency parameter for various types of oil supply configurations. This parameter does not change with the bearing operation conditions. Thus, bearing designers have a new tool that allows the early specification of flow rate as an input parameter, not a consequence of analysis nor a constraint during actual operation.
San Andres, Luis; Abdollahi, Behzad (2018). On the Performance of Tilting Pad Bearings: A Novel Model for Lubricant Mixing at Oil Feed Ports with Improved Estimation of Pads’ Inlet Temperature and Its Validation Against Experimental Data. Turbomachinery Laboratory, Texas A&M Engineering Experiment Station. Available electronically from https : / /hdl .handle .net /1969 .1 /172520.