The Numerical Simulation of Multi-Scale Oil Films Using Coupled VOF and Eulerian Thin-Film Models

Abstract

This paper presents a coupled ETFM-VOF framework for the numerical simulation of multi-scale thin liquid films. A depth-averaged Eulerian thin-film model (ETFM) is used to simulate the oil flow in very thin-film regions where film thicknesses are below the grid resolution while elsewhere in the domain where grid resolution is sufficient to resolve the film, a traditional Volume-of-Fluid (VOF) approach is retained. The two approaches are coupled through momentum and mass conserving source terms and a transition criterion is introduced where the total liquid volume fraction in each cell is evaluated and either the ETFM or VOF approach used depending on the sufficiency of the local grid resolution. Using this approach, thin-film flows characterised by multiple film thickness scales may be reliably simulated at a relatively lower computational cost. The model builds upon currently available ETFM and VOF approaches to thin-film modelling and represents a novel approach to the numerical simulation of multiphase flows involving a varying range of film thickness scales in space and time. A numerical test case of the 3D rimming flow inside an idealised aero-engine bearing chamber has been used to demonstrate the approach and comparisons made against high resolution VOF solutions.

CFD modeling of multiphase flows in the gas turbine engines oil cavities

“…Paper [15] reports an approach to simulate film behavior at the bearing chamber walls, combining the VOF model and the Euler thin-film model (ETFM). Such a model is used for regions with a particularly thin film (less than the height of the mesh cell), and for other regions, where the mesh's resolution is sufficient to describe the thickness of the film, a standard VOF model is used.…”

“…Based on the analysis of the scientific literature [11,15,[18][19][20], preliminary calculations [21][22][23][24], and recommendations on the application of models in Ansys [25], 12 structures of a three-dimensional CFD model were used for this study. The best consistency with experimental data was shown by structures based on the application of the Inhomogeneous (Ansys CFX), Euler and VOF (Ansys Fluent) models.…”

Prediction of Film Thickness of an Aero-Engine Bearing Chamber Using Coupled VOF and Thin Film Model

“…Hence, a reliable and efficient computational model based on computational fluid dynamic (CFD) is much desired to enhance the existing understanding of thin-film hydrodynamics inside the bearing chamber. Building on the previous work of Kakimpa et al [6], a volume-of-fluid (VOF) model coupled with Eulerian thin-film model (ETFM) is implemented to predict the film thickness in an aero-engine bearing chamber. A multi-scale lubricant film is observed in the bearing chamber of an aero-engine.…”

“…Utilizing the VOF approach alone to capture the formation of the thin-film and its interaction with the air-flows induced due to the rotating shaft is too computationally expensive as it requires relatively refined grids to capture the thin oil film. To cope with this difficulty, and to present a fast predictive tool, VOF coupled with ETFM was implemented by Kakimpa et al [6] for rimming flows. A depth-averaged ETFM model is used in the region where oil film thickness is smaller than the affordable grid size required for VOF.…”

Modelling Droplet Heat and Mass Transfer in Aero-Engine Bearing Chambers

“…The impingement of droplets favours the formation of a thin film of oil along the wall surface of the bearing chamber. This has been analysed numerically and experimentally over the past 25 years, mainly by two groups, one of which is the Gas Turbine and Transmission Research Centre (G2TRC) at the University of Nottingham (Williams, 2009, Tkaczyk, 2011, Wang et al, 2011, Bristot et al, 2016, Kakimpa et al, 2016, Crouchez-Pillot and Morvan, 2014 and the other is the Karlsruhe Institute of Technology in Germany (Wittig et al, 1994, Gorse et al, 2004, Hashmi, 2012, Kurz et al, 2013, Kurz et al, 2014, Krug et al, 2015.…”