A model is developed to predict the hydrodynamic performance of a foil journal bearing. The model accounts for both the compressibility of air and the compliance of the bearing surface. A series of predictions of the load-carrying capacity based on the numerical solution for pressure is presented that cover a wide range of operating speeds. The results show good agreement with existing experimental data.
A thermohydrodynamic model is developed for predicting the three-dimensional (3D) temperature field in an air-lubricated, compliant foil journal bearing. The model accounts for the compressibility and the viscosity-temperature characteristic of air and the compliance of the bearing surface. The results of numerical solutions are compared to published experimental measurements and reasonable agreement has been attained. Parametric studies covering a fairly wide range of operating speeds and load conditions were carried out to illustrate the usefulness of the model in terms of predicting the thermal performance of foil journal bearings.
Thermoelastic instability (TEI) in a mechanical component manifests itself in the form of macroscopic hot spots. To gain insight into the mechanism of hot spotting, an engineering TEI model for two solid surfaces separated by a viscous liquid ®lm in relative sliding motion is developed. The model lends itself to a useful analytical expression for determining the threshold of instability with provision for the effect of the migration speed. NOTATION a wave number associated with perturbation in the y direction (m ¡1 ) A amplitude of the perturbed surface temperature (K) A s wetted surface area of the conductor (m 2 ) c migration speed in the local coordinate x direction (m/s) d penetration depth (m) E Young's modulus (N/m 2 ) h total ®lm thickness (m) h 0 perturbation (m) h 0 nominal ®lm thickness (m) k conductivity (W/m K) L radial width of the mechanical seal (m) m width factor of the seal lip p hydrodynamic pressure (Pa) q total heat¯ux (W/m 2 ) q 0 perturbed heat¯ux (W/m 2 ) q 0 nominal heat¯ux (W/m 2 ) Q heat generated (W) t time (s) T 0 perturbed temperature ®eld (K) T 0 s perturbed surface temperature (K) u¯ow velocity in the x direction (m/s) U operating speed (m/s) U cr critical operating speed (m/s) V volume of¯uid (m 3 ) w¯ow velocity in the z direction (m/s) x local coordinate in the moving direction y local coordinate inward normal to the conductor surface z local coordinate into the paper a coef®cient of expansion (K ¡1 ) b stability parameter (s ¡1 ) _ g g viscous strain rate (s ¡1 ) d 0 total surface deformation (m) d 0 e elastic surface deformation (m) d 0 th perturbed thermal expansion (m) k thermal diffusivity (m 2 /s) m¯uid viscosity (Pa s) O wave number associated with perturbation in the x direction (m ¡1 ) t shear stress (N/m 2 ) x spatial growth parameter of the perturbed temperature (m ¡1 )
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