Abstract
During the start-up period, if the journals bearing bushing and shaft materials have different heat conductivities, the thermal expansion of the shaft might be more rapid than that of the bushing. This reduces the radial clearance between the bearing components and generates higher shear stresses in the lubricating fluid, which can lead to bearing seizure, resulting in the deterioration of the journal bearing. (1) First, we present an experimental case study of the seizure of a central groove journal bearing with a carbon-filled polytetrafluoroethylene (PTFE) bushing and a steel shaft; (2) Then, a static thermoelastohydrodynamic (TEHD) simulation is compared to Cristea’s experiments (Cristea, A.-F., 2012); (3) Then, a pseudo-transient TEHD simulation is performed in order to numerically predict the observed phenomena on the test rig; (4) Finally, the evolution of the oil flow rate and the bushing temperatures during the start-up period determined with the pseudo-transient TEHD modelling are compared to the experimental data of the test rig. The pressure field is determined with the thermohydrodynamic (THD) Elrod’s modelling, with Vijayaraghvan’s robust solver algorithm. The pseudo-transient temperature field in the bearing components as well as the thermal and mechanical deformations are calculated with a commercial software.
Highlights
In the aviation industry weight has always been a crucial question
One pseudo-transient TEHD computation is run on an interval of 5 s, the convergence of the corresponding THD simulation in the oil film is executed on the mid-point of the transient thermal computation (Figure 7)
The experiments determined that the current structure of the journal bearing can cause seizure during start-up period
Summary
In the aviation industry weight has always been a crucial question. On one hand, in order to reduce weight, one can find lightened gears, beams and lightened (hollow) shafts. Kucinschi observed several thermal phenomena in the bearing: the clearance closure between the bearing components, the response time of the bearing in case of acceleration or deceleration and the change of load carrying capacity. Their tests displayed a highly different behaviour in the case of a transitional regime than in the permanent cases. A test case for a circumferential groove journal bearing where the closure of the clearance results in seizure between the carbon-loaded PTFE ring and the steel shaft is revealed and discussed
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