5.2. Calculations for the case of sliding surfaces deformations taken into account

The deformations of bearing sliding surfaces should be taken into account in calculations of the characteristics for large carrying force values and for the bearings with low elasticity modulus of the antifriction coating. The gap h for the bearing with compliant surface is not constant, and can be determined from (5). On the basis of the algorithm for calculation of the thrust bear-ing characteristics with the sliding surfaces deformations taken into account, presented in this paper, we carried out the evaluation of contribution of the bearing surfaces deformability to the carrying force. The Calculations per-formed for the 6-lobe bearing with the parameters mentioned above (Fig. 1) with water and oil considered as lubricants. The deformable coating consists of an external PTFE (polytetrafluoroethylene) layer with elasticity modulus of 8 103 MPa, the Poisson ratio equal to 0.375, and an intermediate bronze layer with modulus of elasticity of 1.127 105 MPa and the Poisson ratio of 0.32. The PTFE and the bronze layer thicknesses are 0.025 mm and 0.275 mm, respectively.

The calculations of bearing deformation under the action of the fluid film pressure are carried out with the help of the bearing solid model in a conventional finite-element software. The bearing geometry with the fasteners fixing it to the casing is shown in Fig. 1, the bearing finite-element model and the calculation results for deformations under a 50 kN initial axial load acting on it are shown in Fig. 8.

Unauthenticated

Download Date | 4/15/18 2:31 PM

462 MIKHAIL TEMIS, ALEXANDER LAZAREV

Fig. 6. Thrust bearing stiffness characteristics for selected angles of deflection

Unauthenticated

Download Date | 4/15/18 2:31 PM

ELASTOHYDRODYNAMIC CONTACT MODEL FOR CALCULATION OF AXIAL AND ANGULAR. . .463

Fig. 7. Thrust bearing stiffness characteristics

Unauthenticated

Download Date | 4/15/18 2:31 PM

464 MIKHAIL TEMIS, ALEXANDER LAZAREV

Fig. 8. Finite-element model and total displacements in m under the action of 39,2 kN axial loading

Fig. 9. Thrust bearing carrying force for water lubrication (a) and oil lubrication (b)

The graph of bearing carrying force versus minimal gap before defor-mation for rigid and deformable sliding surfaces is shown in Fig. 9. The calculations were carried out for two lubricant types: water and oil with dy-namic viscosity of 0.001 MPa s and 0.02 MPa s, respectively. The deformed gap and the plots of pressure distribution in the sections that contain the point of maximum pressure on the bearing surface, under initial axial loading of 50 kN, for oil lubrication, are shown in Fig. 10. Fig. 10a correspond to the section with constant radius and Fig. 10b – to the sections with constant angular coordinate. As it can be seen from calculation results, in the case of the small gap that corresponds to high axial loads, the bearing surface deformations have a considerable influence on its stiffness characteristics, particularly on the carrying force.

ELASTOHYDRODYNAMIC CONTACT MODEL FOR CALCULATION OF AXIAL AND ANGULAR. . .465

Fig. 10. Thrust bearing lobe characteristics under the action of 50 kN initial axial loading for the sections passed through point p = pmax

6. Conclusion

A mathematical model of a thrust bearing has been developed. This model, in the presence of axial and angular displacements of the runner, lets one to determine bearing stiffness characteristics with the sliding surfaces deformability and shaft bending taken into account. Verification of the fluid flow model is carried out on the basis of Reynolds equation by comparing its results with experimental and theoretical results from [1]. Numerical simula-tion results obtained via STAR-CD software have confirmed that accuracy of the developed model is sufficient. The dependencies of the bearing carrying force and moment components for a sample bearing structure, are calculated versus minimal gap (hmin), runner angular displacement ( ) and the location of the runner rotation line ( ). They have shown that deformability of the sliding surfaces has a sufficient influence on bearing stiffness characteristics. The developed model is the basis for finite element formulation of the thrust bearing support applicable for the rotor dynamics investigation problem.