S. Busam

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

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.

Local and Mean Heat Transfer Coefficients Along the Internal Housing Walls of Aero Engine Bearing Chambers

A proper matching of the heat transfer to the lubrication oil in bearing chambers and subsequent vent and scavenge pipes is one of the major tasks in the design process of secondary air/lubrication oil systems of modern jet engines. For a calculation of lubrication oil flow rates, which should be kept as small as possible in order to reduce parasitic losses due to larger pumps, filters and coolers, a sufficient knowledge of all heat transfer phenomena involved in bearing chamber flows is required. Beside heat sources such as the bearing friction, the heated sealing air flow and the churning and ventilation of two-phase mixtures, the heat transfer at the housing walls has to be considered. The present paper deals with an experimental investigation of the latter effect based on engine relevant pressure and temperature levels bearing chamber operating conditions. Air/oil flow heat transfer measurements at the internal bearing chamber walls are described utilizing the temperature gradient method. It is a stationary technique based on a two-dimensional finite element calculation procedure.Influences of sealing air flow rate, lubrication oil flow rate and rotational speed on local heat transfer coefficients are discussed. Mean heat transfer coefficients that have been calculated from local data are presented in terms of operational parameters.Copyright

Disintegration of Oil Films Emerging From Radial Holes in a Rotating Cylinder

A fundamental study has been performed to examine the disintegration of oil films emerging from radial holes in a rotating hollow cylinder. The configuration investigated is an ion of one of the droplet generation sources in an aeroengine bearing compartment; similar configurations may also occur inside gearboxes. 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. Similar to a prior paper on droplet generation processes at the rim of a rotating disk (Glahn, A. et al., 2000, Droplet Generation by Disintegration of Oil Films at the Rim of a Rotating Disk, ASME Paper No. 2000-GT-0279.) the near-term objectives of the study are (i) to determine droplet sizes under relevant aeroengine bearing compartment operating conditions, and (ii) to measure individual droplet diameter/velocity relationships. The long-term objective is to incorporate this information into advanced CFD-based design tools. Therefore, special emphasis has been directed towards a correlation of test results that enables determination of boundary conditions for a two-phase (oil droplets/air) simulation of lubrication system components. Based on the results of the present paper, droplet flow boundary conditions in terms of mean diameter, standard deviation of the diameter distribution, starting velocity, and flow angle are available for oil droplets generated by disintegration of oil films emerging from rotating radial holes and rotating disks.

An Experimental Study of Liquid Film Thickness in Annular Air/Oil Flow in a Vertical Pipe Using a Laser Focus Displacement Meter

The development of modern aero-engines is leading to increased pressure and temperature levels which makes increasing demands on the engines’ safety and reliability. In particular the vent-system of the bearing chambers located in the hot section of the engine represents a critical component in the design process due to the complex two-phase flow phenomena. The air/oil mixture that is discharged out of the bearing chambers has a strong influence on the overall pressure losses and it shows locally enhanced heat transfer where oil coking or oil fires with the risk of flashback into the bearing chamber can occur.In order to gain a deeper insight into the interacting flow of air and oil, a glass pipe test section with a inner tube diameter of 10 mm was integrated into the vent-line of the high speed bearing chamber test rig operated at the Institut fur Thermische Stromungsmaschinen, University of Karlsruhe, Germany. Therewith, an experimental study of the oil film along the wall in vertical annular upflow was performed by use of a laser focus displacement meter. This instrument which was introduced by Takamasa et al. [1] allows accurate measurements of film thickness to be made in real time with a sensitivity of 2 microns and a datarate of 1.5 kilohertz.Comprehensive measurements were conducted at two locations of the pipe 320 mm apart in flow direction. A wide range of oil and air flow rates was examined to study their impact on the local film thickness. Both fluids were heated up to the same temperature of 70°C and 100 °C, respectively, to vary the oil viscosity by a factor of 2.Copyright

Disintegration of Oil Jets Emerging From Axial Passages at the Face of a Rotating Cylinder

A fundamental study has been performed to examine the disintegration of oil films emerging from axial passages at the face of a rotating cylinder. The investigation has been conducted in parallel to a similar study on atomization processes at rotating radial holes (Glahn et al. 2001) and has used the same approaches in simulating one of the droplet generation sources in aero-engine lubrication systems. Both papers aim to contribute to the establishment of a database that can be used for the development of droplet generation models directly applicable to engine conditions. As with the parallel investigation, the near-term objectives of fundamental oil film disintegration studies are (i) to determine droplet sizes under relevant aero-engine bearing compartment operating conditions, and (ii) to measure individual droplet diameter/velocity relationships. The long-term objective is to incorporate this information into advanced design systems such as CFD-based tools.In the present study, flow visualization has been used to identify the dominant disintegration processes. Droplet diameters and velocities have been obtained for relevant engine operating conditions. Data are presented in terms of both characteristic diameters and size-class resolved droplet velocities and flow angles. A comparison of droplet sprays measured in the present study with those generated by disintegration of oil films at the rim of a rotating disk (Glahn at al. 2000) has been enabled by introducing non-dimensional parameters for atomization products and operating conditions.© 2001 ASME