Application of the volume of fluid method with heat transfer to a two-shaft aero-engine bearing chamber

Bristot, Andrea (2018) Application of the volume of fluid method with heat transfer to a two-shaft aero-engine bearing chamber. PhD thesis, University of Nottingham.

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The innovations proposed for future civil aero engine concepts are likely to pose new challenges for the oil system. Higher cooling requirements and smaller core sizes mean that an effective use of oil is fundamental to secure the efficiency gains achievable with new designs. The introduction of accurate tools to predict the behaviour of air and oil flows is key to support this process.

Over the past 15 years, several Computational Fluid Dynamics (CFD) techniques have been developed to simulate elements of the air and oil flows in oil system cavities. This process has been incremental and prior to the work presented in this thesis a demonstration of the full application onto a real geometry had not been attempted. This step is necessary to evaluate the challenges still to be addressed for a complete applicability, as well as the relative relevance of the various modelling aspects. Within this framework, this thesis implements the Volume of Fluid (VOF) method for the first time onto a real bearing chamber geometry, namely the Rolls-Royce BR725 Rear Bearing Chamber.

In this work, a preliminary study is performed on a geometrically simplified bearing chamber geometry for which previous experimental data exists to identify the optimal settings and possible challenges before progressing to the real application. The importance of the liquid-gas interface is identified and different interface reconstruction techniques and turbulence damping approaches are tested and developed on this configuration. The results show the relevance of turbulence damping in influencing the flow regime, identifying aspects that could not be predicted from the stratified channel flow tests that have informed previous turbulence damping methodologies.

The implementation on the BR725 builds on these results, additionally introducing polyhedral meshing. Two operating conditions representative of the spectrum of flow regimes are simulated. A wall-fluid heat transfer model is included. The results show good agreement with the design assumptions and experimental data, in particular for flow conditions associated with the “ground idle” engine operating condition. At chamber conditions associated with high power engine operation, the gas-liquid interaction modelling limitations identified in the preliminary study emerge and are investigated. Despite the higher degree of uncertainty on these results, the comparison with the experimental data available shows that a reasonable accuracy is achieved, having selected a suitable level of turbulence damping. The data obtained from the CFD model identified a link between the oil behaviour in the bearing chamber annulus and the frequency content of the scavenge flows.

The work presented in this thesis represents a significant step forward in bearing chamber modelling capability using the VOF method. The results obtained for the BR725 rear bearing chamber will support future research activities as well as design investigations on current bearing chamber problems.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Morvan, Hervé P.
Simmons, Kathy
Keywords: CFD, VOF, Multiphase, Two-phase, Bearing chamber, Shear-driven, Heat transfer, Turbulence damping, Compressive
Subjects: T Technology > TL Motor vehicles. Aeronautics. Astronautics
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 51391
Depositing User: Bristot, Andrea
Date Deposited: 28 Sep 2021 14:06
Last Modified: 28 Sep 2021 14:08

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