Design of an axially concave pad profile for a large turbine tilting-pad bearing

Abstract

To improve operational safety and/or achieve a higher load capacity of turbine tilting-pad bearings, an axially concave pad profile is presented. The thermal and mechanical stress of the loaded pads of a test bearing in load between pivot configuration has been analysed. Both film thickness and pressure distribution have been measured at a very high resolution. A fluid film calculation program in combination with a finite-volume-based structural mechanics program is used to simulate the deformation of a single pad under high circumferential speeds. In this context, the axial and tangential heat transfer coefficients of the pad surface, which act as boundary conditions for the calculation of the 3D temperature distribution, are determined using an optimization process. Herein, the match of predicted and measured pad temperatures is the goal. It can be shown that there must be a huge difference in heat transfer in axial and tangential direction in order to match the large measured temperature gradient in circumferential direction. Based on the measured deformed profile the program code is used to derive a concave pad profile, which will result in an axially non-arched sliding surface under the expected thermal load. Therefore, an iterative simulation procedure is used. By decreasing the axial arching of the pad and thus the large film thickness at the axial ends using an improved profile designed for a specific operation point, the minimum film thickness and maximum pad temperature can be influenced beneficially. The comparison of measurement data and calculation results shows very good agreement regarding the pad deformations. The results indicate that by axially concave profiling of the loaded pads of a large tilting-pad bearing for a specific operation point, the static characteristics in the form of temperature, film thickness and load capacity can be improved.

Influence of Active Cooling at the Trailing Edge on the Thermal Behavior of a Tilting-Pad Journal Bearing

“…The calculation procedure and the results are also discussed in the publications of Hagemann et al [16] and Kukla et al [17] and show good agreement between calculation results and experimental data. Kukla et al [18] apply an optimization procedure to the same ∅-500 mm five-pad TPJB already used by Hagemann [5]. They determine the HTC at the free pad surfaces by minimizing the deviations between measured and calculated measuring point temperatures.…”

Revealing deformation of segments and their supports in a hydrostatic segmental bearing

“…The study results have shown that reduction of bearing surface temperature achieved by optimized vortex grooves resulted in a significant increase in bearing capacity. Thermal deformations of slider bearing pads of a powerful turbine are considered in [13]. Comparison of measurement data and calculations is given which showed good conformance for thermal deformations in pads.…”

“…Elastic deformations of the segments were calculated using expressions (5), (13), and (15). Deformations were calculated for the most loaded lower segment in which pressure in the chambers at large eccentricities was close to the feeding pressure of the working fluid.…”

Behavior of Lubricated Bearings in Electric Circuits

“…The models of Furtmann [1,2] and Gemeinder [3] are based on the consideration of the loaded rolling elements only; Schirra extends the approach by including the load-free rolling element contacts for sensory purposes [6,7]. For journal bearings, due to the absence of rolling elements and the rather plain bearing surfaces, more sophisticated models, such as the cylinder capacitor, can be used to achieve a good agreement between model predictions and test rig measurements, e.g., for the lubricating film thickness or other operation conditions [8][9][10][11]. However, such methods cannot be used for insulating coatings, such as those found in tilting pad bearings with, e.g., PEEK thrust pads forming an extra capacitor arranged in series with the lubrication film.…”