Highly transient squeeze-film flows

Abstract

The aim of this work was to investigate the flow evolution with time of fluid between two parallel disks and the corresponding pressure variations at the centre of the lower disk that occur subsequent to an impact-loading situation arising from dropping a mass onto the upper disk from a chosen height. During the event a fixed amount of energy is dissipated in the fluid between the disks through the action of friction. Therefore, this fundamental system may be regarded as a constant energy one, as distinct from one in which the upper disk is moving at a constant velocity, or is acted upon by a constant force. A test cell was set up to conduct the investigation, for which the separation between the disks was monitored, together with the pressure at the centre of the lower disk, over the duration of the experiment (about 8–10 ms). Glycerine was used as the test fluid. The equation of motion, based on a self-similarity approach, was reduced to a simpler (quasi-steady linear or QSL) form. Measured values of disk separation, velocity and acceleration were substituted as inputs into the full QSL model and two limiting cases, namely an inviscid and a viscous model. The QSL model provided excellent comparisons between the pressure measurements and data generated by a commercial computational fluid dynamics software package, throughout the duration of a typical experiment. The inviscid and viscous models achieved good correlations with measurements for the initial impact (during which disk accelerations exceeding 2 km s−2 occurred) and towards the end of the event, that were characterized by a small and much larger pressure rise, respectively. The former feature appears not to have been previously reported and is likely to typify that which would be observed in impact systems involving squeeze films.