Tilting-Pad Journal Bearing in Hybrid Operation: A Numerical and Experimental Investigation

Abstract

Large turbine bearings are usually equipped with hydrostatic jacking mechanisms to separate bearing and shaft during transient start-stop procedures. They are turned off once hydrodynamic operation is reached. In some cases, under severe operating conditions, the hydrostatic oil supply is kept running although the rotor already runs in full speed. The supplied amount of jacking oil is very small compared to the regular oil supply. However, experimental data of a large tilting-pad bearing shows that this hybrid operation has a considerable impact on the load carrying capacity in terms of lower pad temperature and larger film thickness. In this paper, a theoretical investigation to analyse the effect of increased load carrying capacity of a large tilting-pad journal bearing in hybrid operation is presented. The increase is driven by three different aspects: 1) hydrostatic pressure component, 2) increase in lubricant viscosity due to the injection of cold oil, 3) decrease of temperature gradients and thus thermal pad deformation. Subject of the approach is a ø500 mm five-pad, rocker-pivot tilting-pad journal bearing in flooded lubrication mode. The experiments are carried out on the Bochum test rig for large turbine bearings. The theoretical analyses are performed with a simulation code solving the Reynolds and energy equations for the oil film and calculating the thermomechanical pad deformations simultaneously. By considering each of the three above aspects separately and in combination, their share of load increase can be assessed individually. Contrary to expectations, the results indicate that the increase is not mostly based on the hydrostatic pressure component. Instead, the advantageously decreased pad deformations make the largest contribution to the increased load carrying capacity while the alteration in viscosity shows the least impact.

Influence of Injection Pressure on the Thermohydrodynamic Behavior of Tilting Pad Journal Bearings—Model and Experiment

“…Still considering the application of hydrostatic jacking mechanisms, Buchhorn et al [21] perform theoretical and experimental investigation varying the hydrostatic pressure, increasing the lubricant viscosity due to the injection of cold oil, decreasing the temperature gradients and, consequently, the thermal pad deformation. The authors concluded that load-carrying increase is not mostly based on the hydrostatic pressure component, since the decreased pad deformations make the largest contribution.…”

Анализ Работы Опорных Подшипников Турбомашин На Экологически Чистых Жидкостях

“…Втім, основний недолік використання води та інших малов'язких водних розчинів для роботи підшипників ковзання полягає в недостатньому гідродинамічному ефекті при малих частотах обертання ротора під час пуску і зупинки турбіни. Тому робота підшипника в режимах пуску і валоповороту, а також при вибігу валопроводу, можлива, зокрема, з використанням гідростатичного підйому ротора [6,7]. При досягненні певної частоти обертання ротора гідропідйом відключається, а гідродинамічний тиск, що розвивається в мастильному шарі підшипника, стає достатнім для створення необхідної товщини мастильного шару, яка забезпечує надійну роботу підшипника [8].…”

Measured and Predicted Operating Characteristics of a Tilting-Pad Journal Bearing with Jacking-Oil Device at Hydrostatic, Hybrid, and Hydrodynamic Operation

“…Beside their nominal applications, lift-oil devices can be used as a short-term measure if field issues occur. Buchhorn et al [8] report on a reduction of maximum measured pad temperature by up to ∆T = 10 K by activating the hydrostatic assistance system at rated operating conditions of a large turbine tilting-pad journal bearing. The authors relate this behavior to a combined effect of thermo-hydrodynamics and deformation.…”