1. Machine Elements, Luleå University of Technology
CFD simulation of non isothermal turbulence in LEG Tilting Pad Bearings
Philip Croné, Andreas Almqvist & Roland Larsson
Machine Elements, Luleå University of Technology

2. Objectives
Modelling a Leading Edge Grooved (LEG) segment of a Tilting Pad Bearing to include thermal and turbulence effects

3. Objectives Classic Approach [1] This paper Reynolds Equation
Approximative Energy Equ.
Inlet temperature BC
3D CFD
Full Energy Equation
State-of-the-art Turbulence model
Two methods
Leading Edge Groove Geometry
Effective inlet temperature BC
How does the two approches compare?
&
[1] Dmochowski, W. K. S. A., Brockwell, K., DeCamillo, S., & Mikula,
A. (1993). A study of the thermal characteristics of the leading edge groove and conventional tilting pad journal bearings. Journal of tribology, 115(2),

4. Modelling of a Leading Edge Grooved Tilting Pad segment:
Objectives
Modelling of a Leading Edge Grooved Tilting Pad segment:
Does the LEG cause a higher level of turbulence in the lubricant as sugested by M. He in [2]?
Is there a large discrepancy between the temperature predicted by
1) An effective BC calculated with a mixing equation
2) Modelling the actual LEG geometry
[2] He, M., Allaire, P. E., Barrett, L., & Nicholas, J. (2002, September). TEHD modeling of leading edge groove tilting pad bearings. In 6th International Conference on Rotor Dynamics (IFTOMM), Sydney, Sept.

5. Geometry
Note that only half of the axial length is included due to symmetry
Pad B (LEG)
Pad A

6. Model Mean Velocity and Pressure: SST Turbulence model (1) (2) (3) (4)
Reynolds averaged (RANS) two equation eddy viscosity model
(1)
(2)
(3)
(4)
(5)
(6)

7. Model
Mean Temperature: Reynolds averaged Energy equation
(7)
(8)
(9)

8. Model
The tilting angle is found by imposing a moment equilibrium around the pivot
Shaft excentricity fixed at ~ 0.5 of Cb
A mixing model is used for the leading edge temperature in Pad A

9. Model
Inlet conditions :

10. Model
Inlet temperature:

11. Simulation
The governing equations were solved using the commercial FE software Comsol Multiphysics
Operating speed: 3000 rpm
Lubricant ISO VG 32
Shaft diameter: 0.5 m
Axial length: 0.35 m
These conditions results in a shaft surface speed of m/s!
Use of a turbulence model is justified, [3].
[3] Gardner, W. W., & Ulschmid, J. G. (1974). Turbulence effects in two journal bearing applications. Journal of Lubrication Technology, 96(1),

12. Simulation-Mesh
The outcome of the simulations is very sensitive to the mesh resolution in the near wall region.
At most, 12 elements, most of them clustered near the wall, were used across the thickness of the lubricant domain.
This was deemed an acceptable trade-off between accuracy and convergence rate
Pad B (LEG) mesh
Pad B (LEG) zoom in on boundary layer mesh

13. Simulation- Results

14. Simulation- Results
Comparison between film thickness for the cases studied

15. Simulation-Results
Comparison between surface pressure for the cases studied

16. Simulation-Results
Comparison between surface temperature for the cases studied

17. Simulation-Results
Comparison between the turbulent to molecular dynamic viscosity ratio

18. How does the dimensions of the LEG portion influence the results?
A parameter study was performed where the circumferential length of the LEG portion was diminished.
The influence of groove depth was also studied

19. Simulation-Results 2
Diminishing the LEG portion!

20. Simulation-Results 2 OG>Geom2>Geom3>Geom4>Geom5>Geom6
Influence on turbulence by shrinking the LEG portion

21. Simulation-Results 2
Influence on metal temperature by shrinking the LEG portion

22. Simulation-Results 2
Diminishing the groove depth!

23. Simulation-Results 2 Groove depth: Geom6>Geom7>Geom8
Influence on turbulence by shrinking the groove depth

24. Simulation-Results 2
Influence on metal temperature by shrinking the groove depth

25. Simulation-Results 3 What if we increase the rotational speed?
Influence of rotational speed on turbulence level, comparison between
Pad B (LEG) and Pad A at a speed ranging from RPM=

26. Conclusions
The simulations suggest that NOT including the LEG geometry underestimates pressure, temperature and film thickness.
Not modelling the LEG geometry predicts a higher level of turbulence, using the current (SST) model.
A nice bonus in including the LEG is that the ram pressure inherently gets included.

27. Acknowledgements
This research was conducted using the resources of High Performance Computing Center North (HPC2N)
5th International Computational on Contact Mechanics 5-7 July 2017, Lecce

28. Thank you for your attention!
Questions?
Philip Croné