arXiv subjects

Pascal Jolly

Publications and source records attributed to Pascal Jolly.

2 recordsLinked to original sources

arXiv2025

The Thermal Unbalance Effect Induced by a Journal Bearing in Rigid and Flexible Rotors: Experimental Analysis

The present work presents the experimental analyses of a rigid (short) and a flexible (long) rotor subject to thermal unbalance effects. The rotors are supported by a ball bearing and by a cylindrical journal bearing. The differential heating generated in the journal bearing is responsible for the thermal unbalance. The results obtained with the short rotor at 7 krpm showed an increase in the synchronous amplitudes but slight phase changes before stabilization. The pronounced hysteresis of the synchronous amplitudes obtained during coast-down proved that the amplitude increase is due to the thermal unbalance. The results obtained for the long rotor at 6.6 krpm showed the same stabilized response when start-up was performed in 180___s. However, an instability leading to journal bearing contact was triggered when the start-up time was decreased to 80___s. The presented experimental results are the synchronous amplitudes and phases, the mean temperatures, and the maximum temperature differences of the journal and of the bearing and the phase lags between the high spot and the hot spot.

physics.class-ph↗

arXiv2024

Slip Length in Shear Flow Over a Textured Surface

Hydrophobic textured surfaces are studied for their low wettability and their capacity to create a 'slippery' fluid on the surface during lubrication. To this end, the flow between two parallel surfaces is numerically addressed by computing two-dimensional numerical simulations. One of the surfaces moves with a uniform rectilinear motion, while the other is fixed, with a cavity in the middle. The steady-state flow is laminar and monophasic with a low Reynolds number. The reduction of the wall shear stress caused by a vortex in the cavity, with respect to a Couette flow, looks like the creation of an equivalent slip of the fluid on the wall at a macroscopic scale.Three methods are used to calculate the slip length: one is based on the wall shear stress and the other two are based on the speed of the fluid flow. When the slip length is calculated according to these three methods, the obtained results differ. The differences show that the slip often used in the literature is a macroscopic representation of local effects that are not necessarily slippery. The speed profiles and the streamlines are then discussed, in order to propose an explanation for this difference.

physics.flu-dyn↗