Droplet Generation by Disintegration of Oil Films at the Rim of a Rotating Disk

Abstract

A fundamental study has been performed to examine oil film disintegration mechanisms at the rim of a rotating disk. The configuration investigated is an abstraction of one of the droplet generation sources in an aeroengine bearing compartment. The paper aims to contribute to both the determination of directly applicable droplet characteristics and the establishment of a database that can be used for the development of droplet generation models. The near-term objectives of the study are (i) to identify disintegration modes relevant with respect to aeroengine bearing compartment operating conditions, (ii) to determine droplet sizes under those operating conditions, and (iii) to measure individual droplet diameter/velocity relationships. The long-term objective is to incorporate this information into advanced CFD-based design tools. The disintegration modes identified here were similar to previously reported flow regimes generated by rotary atomizers. However, slightly different transition characteristics are documented for the turbine oil considered here, indicating a transition occurring at either higher speeds or higher flow rates. Droplet diameters and velocities are presented for relevant bearing compartment conditions. In this mode, droplet diameters appear to be insensitive to the volume flow rate, but show a finer atomization for increasing rotational speeds. Eventually a speed is reached beyond which no further droplet diameter reduction is obtained. For the first time, size class resolved droplet velocities are presented. A variation of operating parameters at a constant radial location does not have a significant impact on either the normalized droplet velocity or the flow angle. Radial traverses show a decrease of the droplet velocity with increasing distance from the rim of the disk and a transition from a more tangentially oriented droplet trajectory to a more radial motion.

Ligament and Droplet Generation by Oil Film on a Rotating Disk

“…It was observed that the oil droplets were shed at the edge of collector outer. Glahn et al [5] found that the droplet generation process in the bearing chamber was similar to the liquid atomization process in a rotary atomizer; therefore, a rotating disk chamber test rig was built [6,7]. The documentation of oil droplets generation around the rotating disk was obtained.…”

Towards Investigation of External Oil Flow From a Journal Bearing in an Epicyclic Gearbox

“…It should be noted that the characteristic numbers obtained for this specific case of journal bearing operation are outside the range of characteristic numbers investigated by [10] and [11]. However, since ̇+ is one and three orders of magnitude larger than the transition value, some confidence can be gained that the actual flow regime is in fact sheet formation.…”

“…This temperature was used to simulate liquid properties similar to those of existing experiments and thus, enable comparison to flow behaviors observed on rotating disks and cups [8], [9], [10], [11]. It should be noted that this temperature is not representative of any typical journal bearing operating temperature.…”

“…Assuming that the simulated flow behaves like flow over a rotating cup [10] or disk [11], the expected flow regime can be determined by comparing the non-dimensional flow rate ̇+ with the transition flow rates ̇1 + and ̇2 + . For ̇+ <̇1 + direct droplet formation is expected, for ̇1 + <̇+ <̇2 + ligament formation is expected and for V̇2 + < V̇+ sheet formation is expected.…”

“…A fundamental study of oil film disintegration at the rim of a rotating disk has been performed by [11]. The configuration was an abstraction of a typical droplet generating source in a jet engine bearing chamber.…”