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This study considers the extent to which the coupling of the governing equations influences the fluid dynamics of a large-scale turbo generator journal bearing. The study was conducted by formulating and implementing four fluid models in the OpenFOAM open-source CFD package. The fluid models are constructed so that uncoupled, weakly-coupled and strongly-coupled model formulations can be studied. To reduce the computational costs, a three-dimensional region of the oil film was extracted and considered. This small region was selected because the computational costs would have been extremely high for a full-scale simulation. To this end, the section selected for extraction was the region where the fluid dependencies are known to exert the greatest influence on the fluid behaviour. It was found that for both the weak-coupled and strong-coupled models, the coupling influenced the flow significantly. The extent to which the coupling influenced the fluid behaviour was seen to be dependent on the strength of the coupling, the dependency that introduced the coupling as well as the formulation of the fluid model. The weak-coupling introduced a greater qualitative change where the influence of the coupling was up to half the influence of the pressure dependence. The strong-coupling showed a greater change in the fluid behaviour and the flow departed non-uniformly from the uncoupled models. [ABSTRACT FROM AUTHOR]

The paper suggests the methodology of computational investigation of fluid and gas flow in the crescent-shaped gap of turbogenerator oil-free bearing on the basis of ANSYS CFX package. Numerical computation data have good convergence with empirical results obtained by other scientists for the same objects. Verification data prove the possibility of computational methodology implementation, at the first stage, in a limited sphere of engineering applications, particularly, when designing cooling systems for eccentric annulus of oil-free friction assemblies. [ABSTRACT FROM AUTHOR]

A hydrogen-cooled turbogenerator operating at 3600 rpm showed the phenomenon of spiral vibration with a forward rotating unbalance vector. The relative shaft vibration measured at the non-driven end-bearing was close to the trip level. Spiral vibration is observed at various types of rotating machinery with both rotation directions of the unbalance vector, i.e., forward and backward. Spiral vibration is caused by a vibration-induced hot spot on the shaft surface generated by friction. The turbogenerator has three bearings: two main bearings and the brush gear bearing. The carbon brushes sliding on the slip rings were identified as the hot spot location. Potential modifications were studied using hot spot stability analyses with a rotor dynamic model of the generator rotor on three journal bearings. The applied method, introduced by Schmied (1987, "Spiral Vibrations of Rotors" Proc. llth Biennial ASME Design Engineering Div. Conf, Vib. Noise, DE-Vol. 2, Rotating Machinery Dynamics, Boston, MA, ASME HO4OOB, pp. 449- 456), allows the handling of general systems. The hot spot model is based on the theory of Kellenberger (1978, Ingenieur-Archiv, 47, pp. 223-229; 1980, Journal of Mechanical Design, 102, pp. 177-184) using a thermal equation between the shaft's thermal deflection and the shaft displacement at the hot spot location. Three different relations between the heat input and the shaft vibration were modeled: heat input proportional to the shaft displacement, to the shaft velocity, and to the shaft acceleration. The model, in which the heat input is proportional to the velocity, is the most suitable variant for slip rings. This was confirmed by comparison with the measured vibration behavior. A modification of the shaft line was selected based on the calculation results and was successfully implemented. This generator and other generators with the same modified brush gear unit have been in operation for more than four years. [ABSTRACT FROM AUTHOR]

Bearing dynamic characteristics have been a major unknown in the modelling and analysis of large turbo-generators. An identification algorithm for bearing dynamic characterization by using unbalance response measurements is developed for multi-degree-of-freedom (m.d.o.f.) flexible rotor-bearing systems. The algorithm identifies the bearing dynamic parameters, consisting of four effective stiffness and four damping coefficients for each bearing, utilizing frequency domain synchronous unbalance response measurements from the accelerometers attached to the bearing housings in the horizontal and vertical directions, for a minimum two different unbalance configurations. The procedure of identifying bearing dynamic coefficients by using the proposed algorithm is presented and demonstrated through a numerical example. Adding noise to the simulated signal checks the robustness of the algorithm against measurement noise. Combinations of regularization and the generalized singular value decomposition (SVD) are used to tackle an ill-posed problem due to the nearly circular orbit of the rotor at the bearings, as a special case for nearly isotropic bearings. It is demonstrated that by measuring noisy bearing responses with the direction of rotation of the rotor both in the clockwise and anticlockwise directions, the bearing estimation problem for circular orbit becomes well-conditioned. The regularization algorithm is tested for an experimental rotor-bearing rig. The response reproduction capabilities are excellent even in the presence of measurement noise. [Copyright &y& Elsevier]