Abstract
Hydraulic seals can be created between two shafts co-rotating at different speeds to provide a zero flow air seal across the annular cavity and these are often used as intershaft seals in aero-engines. These seals are formed between an oil filled trough on the higher speed shaft and a fin on the lower speed shaft that dips into the oil. Rotation is imparted to the sealing fluid within the trough due to the centrifugal force and the seal is able to balance a pressure difference similar to a manometer in operation. To minimize the effects of viscous heating generated by the interaction of the rotating surfaces and the oil, and to reduce oil residence time, a continuous jet-delivered oil feed is usual in aero-engine seals.
Previously published work, has established a successful modelling methodology to evaluate the maximum pressure capability of hydraulic seals when there is no oil feed. Expanding on prior studies, in this current research a relevant continuous through-flow oil feed is added to the seal modelled in Ansys FLUENT to create a model of the oil behaviour in the seal. The numerical simulations are based on a model representative of a hydraulic seal configuration investigated in an experimental study at the University of Nottingham. The CFD study shows the oil flow breaking up into droplets/ligaments followed by the oil film formed around the circumference of the trough using a Volume-of-Fluid (VOF) method when an operational differential pressure is maintained across the seal. Analysis on the size and trajectory of the droplets generated through splashing is reserved for future work.
This paper presents a quantitative evaluation of the disturbance created on the surface by the jet, demonstrating that the greatest disturbance is caused at the point of impact and the oil film thickness is only impacted by a negligible variation of +/− 0.1mm downstream. High quality CFD images of the jet impact behaviour compare with experimental results. The CFD results of the jet penetration and influence of the secondary flow are presented and discussed.
The second part of the paper comprises an investigation into thermal effects including oil-related heat transfer in the modelled hydraulic seal.
