To create an adequate computational model of oil behaviour in an aeroengine bearing chamber previous work at the Gas Turbine and Transmissions Research Centre (G2TRC) suggests it is necessary to be able to model oil shedding from bearings, breaking up into droplets/ligaments and forming thin and thick films driven by gravity and shear. Our previously published work using Fluent successfully coupled volume of fluid with the Eulerian thin film model (ETFM) and identified the challenges coupling the ETFM with the discrete phase modelling (DPM). For this latter work comparison was made to published experimental and modelling data in which a jet is injected into a duct breaking up into droplets before forming a wall film.
In this paper the use of the open-source CFD code OpenFOAM is investigated for this application recognising that such an approach eliminates some of the restrictions in a commercial product. A transient solver for spray particle cloud modelling and thin liquid film transport (sprayParcelFilmFoam) has been developed and incorporated within OpenFOAM. Fully coupled DPM-ETFM is presented, capable of modelling both primary atomization and secondary breakup. In addition two new film sub-models have been implemented for film stripping and edge separation. In order to achieve accurate statistical representation of droplets, modifications to the DPM particle injector code were implemented.
CFD results are validated against published high speed imaging and phase Doppler experimental data and in addition there is a comparison to computational results obtained using ANSYS Fluent. The fidelity of both the solver and the novel surface film sub-models are evaluated against average film thickness measurements along the duct centreline. With the inclusion of both film stripping and edge separation, a normalized root mean squared deviation of 5.1 % was achieved when compared to film thickness measurements, improving significantly on the results obtained with Fluent. A comparison with experimental data of particle diameters and velocities downstream of the expansion edge gives good qualitative agreement. Future work is recommended to provide a better formulation for the edge-separated droplet diameters. Analysis of film momentum source terms highlights the necessity for including both the gas and hydrostatic pressure source terms within the film momentum transport equation.
This CFD investigation has successfully established a fully coupled two-way DPM-ETFM approach. This work illustrates an advance in bearing chamber modelling capability and has established a necessary foundation for future aeroengine bearing chamber film modelling.