Experimental Investigation and Numerical Modelling of a Large Heavily-Loaded Tilting Pad Journal Bearing With Polymer Lined Pads

The increasing share of renewable energy on the electric grid makes the supply side of the grid less predictable. Faster ramping and increased cycling enable fossil fuel plants to balance the fluctuating renewable energy from solar and wind. Operational flexibility is therefore the key need in the current market for power generation. Among these new requirements, also efficiency, compactness and reliability play an important role, which results in an increasing demand for large heavily loaded tilting pad journal bearing (TPJB) with an extended lifetime. In this context, TPJBs can be subjected to high pad temperature which may lead to premature degradation of the pad surface.

Compared to traditional whitemetal lined bearings, polymer-lined bearings are generally known to have higher load carrying capacity because of their higher surface temperature limits and superior boundary lubrication characteristics that are useful at start-up [1].

A large TPJB s with polymer “PEEK” lined pads was successfully tested over a wide range of operating conditions representative of large rotating equipment. The test-bearing has four offset-pivot pads, ball and socket pivots, load-between-pads configuration, directed lubrication and hydrostatic jacking grooves. This bearing design is well-known in the industry and has a successful history in the power generation and oil-gas field over the last decades. The test-rig shaft diameter is 500mm [2] and pad length equals to 350mm (L/D = 0.7). The operating conditions explored during the test campaign characterize the static and dynamic behaviour of the bearing over a broad range of speed and load: shaft surface speed tested between 40 m/s and 95 m/s, max. specific load up to 4.75MPa. Similar test conditions were previously investigated on the same bearing with whitemetal lined pads, allowing for a direct comparison.

In addition to a comprehensive testing of the test article, an accurate prediction of the bearing performances through a numerical model remains of vital importance to guarantee safe operation, specifically with regard to maximum pad temperature and minimum oil-film thickness. A thermoelastohydrodynamic model for TPJBs with polymer lined pads is introduced in this paper and successfully validated against experimental test data. Comparison between numerical results and experimental test data are presented and discussed in detail.

The model introduced here couples the generalized Reynolds equation with a 3D heat transfer analysis and 3D structural-mechanics model of the pad. The 3D heat transfer model analyses the mutual influence between the pad and oil-film thickness, where the energy transport equation for the oil-film thickness and the heat transfer problem of the pads are simultaneously solved, considering different material properties for the backing and lining. The 3D structural-mechanics model estimates the mechanical deformation due to the pressure and thermally-induced deflection of the pad. A special attention is dedicated to the material properties used for the PEEK layer.

Experimental data along with numerical results reveal and confirm enhanced performances for TPJB with polymer-lined pads at heavy-load compared to traditional steel/whitemetal pads.

References

[1] Pethybridge G., New N. (2004) Polymer bearing for severe operating conditions, Proceedings of EDF-LMS Workshop: “Improvements of bearing performance under severe operating conditions”, Poitiers, paper D, pp. 1-6.

[2] Kukla, S., Buchhorn, N., & Bender, B. (2017). Design of an axially concave pad profile for a large turbine tilting-pad bearing. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 231(4), 479–488.