scholarly journals Simulation of a Simplified Aeroengine Bearing Chamber Using a Fully Coupled Two-Way Eulerian Thin Film/Discrete Phase Approach Part I: Film Behaviour Near The Bearing

2021 ◽  
Author(s):  
Andrew Nicoli ◽  
Kathy Johnson ◽  
Richard J Jefferson-Loveday
Keyword(s):  
Thin Film ◽  
Experimental Data ◽  
Film Thickness ◽  
Gas Turbine ◽  
Residence Time ◽  
Research Centre ◽  
Shaft Speed ◽  
Oil Flow ◽  
Discrete Phase ◽  
Fully Coupled

Abstract Previous work at the Gas Turbine and Transmissions Research Centre (G2TRC) has highlighted the need for an adequate computational model that can appropriately model the oil shedding behaviour from bearings. Oil can breakup forming droplets and ligaments, subsequently forming thin and thick films driven by both gravity and shear. Our previously published work using OpenFOAM successfully coupled the Eulerian thin film model (ETFM) with the discrete phase model (DPM) [1]. In this paper, the previously developed ETFM-DPM capability is, for the first time, extended to an aeroengine representative bearing chamber configuration. The configuration matches that of a simplified aeroengine bearing chamber that has been investigated by researchers at the Gas Turbine and Transmissions Research Centre (G2TRC). Numerical investigations are conducted for three different shaft speeds: 5,000, 7,000 and 12,000 rp; at two oil flow rates: 7.3 l/min and 5.2 l/min. CFD results are validated against existing experimental data for the two lower shaft speeds. Evaluation of computed mean film thickness shows excellent agreement with the experimental data. Results show that there is a diminishing reduction of film thickness with an increasing shaft speed. The computational study allows investigation of oil residence time in the annulus near the bearing. Residence time is seen to reduce with increasing shaft speed and with increasing oil flow rate. This CFD investigation represents the first successful fully coupled two-way ETFM-DPM investigation for bearing chamber applications, establishing a firm foundation for future aeroengine bearing chamber modelling.

scholarly journals Simulation of a Simplified Aeroengine Bearing Chamber Using a Fully Coupled Two-way Eulerian Thin Film/Discrete Phase Approach Part II: Droplet Behaviour in the Chamber

2021 ◽  
Author(s):  
Andrew Nicoli ◽  
Kathy Johnson ◽  
Richard J Jefferson-Loveday
Keyword(s):  
Thin Film ◽  
Film Surface ◽  
Research Centre ◽  
Operational Parameters ◽  
Axial Loads ◽  
Two Phase ◽  
Oil Flow ◽  
Discrete Phase ◽  
Edge Separation ◽  
Fully Coupled

Abstract Within aeroengines, bearing chambers exhibit a highly complex two-phase environment as a result of the complex air/oil interactions. The desire to operate at higher temperatures and shaft speeds requires sufficient understanding of these systems for design optimisation. Typically, bearings are used to support the radial and axial loads transmitted by the shafts, requiring oil for lubrication and cooling. These bearings are housed in bearing chambers sealed using airblown seals. Efficient scavenging systems ensure the oil is collected and returned to tank avoiding any unnecessary working of the oil. Previous work at the Gas Turbine and Transmissions Research Centre (G2TRC) has highlighted the need for an adequate computational model that can appropriately model the oil shedding behaviour from such bearings. Oil can breakup forming droplets and ligaments, subsequently forming thin and thick films driven by both gravity and shear. The objective of this paper is to explore the modelling capability of fully two-way coupled Eulerian thin film/discrete phase models (ETFM-DPM) applied to our simplified bearing chamber configuration. The models are created using OpenFOAM and two-way coupling is employed, enabling Lagrangian droplets to either impinge on the film surface or be removed through effects such as film stripping, splashing or edge separation. This paper focuses on the droplets, presenting statistics relating to size, velocity, impingement and residence time providing insight into solution sensitivity to operational parameters including shaft speed and oil flow rate. This extends upon our previously published work and improves bearing chamber modelling capability.

A New OpenFOAM Solver Capable of Modelling Oil Jet-Breakup and Subsequent Film Formation for Bearing Chamber Applications

2019 ◽  
Author(s):  
Andrew Nicoli ◽  
Richard Jefferson-Loveday ◽  
Kathy Simmons
Keyword(s):  
Experimental Data ◽  
Film Thickness ◽  
High Speed ◽  
Surface Film ◽  
Thin Liquid Film ◽  
Research Centre ◽  
Source Terms ◽  
Thickness Measurements ◽  
Edge Separation ◽  
Fully Coupled

Abstract 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.

A New Postulation of Viscosity and Its Application in Computation of Film Thickness in TFL1

2002 ◽  
Vol 124 (4) ◽  
pp. 811-814 ◽  
Author(s):  
Chaohui Zhang ◽  
Jianbin Luo ◽  
Shizhu Wen
Keyword(s):  
Thin Film ◽  
Experimental Data ◽  
Film Thickness ◽  
Solid Surface ◽  
Contact Area ◽  
Elastohydrodynamic Lubrication ◽  
Thin Film Lubrication ◽  
Lubrication Film ◽  
Viscosity Modification ◽  
Film Lubrication

In this paper, a viscosity modification model is developed which can be applied to describe the thin film lubrication problems. The viscosity distribution along the direction normal to solid surface is approached by a function proposed in this paper. Based on the formula, lubricating problem of thin film lubrication (TFL) in isothermal and incompressible condition is solved and the outcome is compared to the experimental data. In thin film lubrication, according to the computation outcomes, the lubrication film thickness is much greater than that in elastohydrodynamic lubrication (EHL). When the velocity is adequately low (i.e., film thickness is thin enough), the pressure distribution in the contact area is close to Hertzian distribution in which the second ridge of pressure is not obvious enough. The film shape demonstrates the earlobe-like form in thin film lubrication, which is similar to EHL while the film is comparatively thicker. The transformation relationships between film thickness and loads, velocities or atmosphere viscosity in thin film lubrication differ from those in EHL so that the transition from thin film lubrication to EHL can be clearly seen.

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

2019 ◽  
Author(s):  
Kuldeep Singh ◽  
Medhat Sharabi ◽  
Stephen Ambrose ◽  
Carol Eastwick ◽  
Richard Jefferson-Loveday
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Air Flow ◽  
Shaft Speed ◽  
Oil Film ◽  
Film Model ◽  
Thin Film Model ◽  
Wide Range ◽  
Aero Engine ◽  
Engine Bearing

Abstract In the present work, a coupled volume-of-fluid (VOF) model with Eulerian thin-film model (ETFM) approach is used to predict the film thickness in an aero-engine bearing chamber. Numerical studies are conducted for a wide range of shaft speeds with lubricant and air flow rates of 100 1/hr and 10 g/s respectively, at a scavenge ratio of 4 on a simplified bearing chamber test rig. Air-flow analysis inside the bearing chamber is also assessed. Primary and secondary airflow predictions are found to be in good agreement with the experimental results. The coupled ETFM+VOF approach is found to be sensitive enough to capture the qualitative trend of oil film formation and distribution over the chamber wall. Oil collection near the sump at a low shaft speed and a rotating oil film at a higher shaft speed are well captured.

Experimental and Numerical Study of the Hydrodynamics of a Thin Film Reactor (TFR) for the Decarboxylation of Anacardic Acid

2017 ◽  
Vol 16 (3) ◽  
Author(s):  
L. Shrutee ◽  
Tim Van Geel ◽  
Eldon R. Rene ◽  
B. Raj Mohan ◽  
Abhishek Dutta
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Residence Time ◽  
Wall Temperature ◽  
Numerical Study ◽  
Strong Dependence ◽  
Rheological Behaviour ◽  
Anacardic Acid ◽  
Lower Velocity ◽  
Film Reactor

AbstractA newly designed laboratory scale thin film reactor (TFR) was tested for the decarboxylation of anacardic acid in Cashew Nut Shell Liquid (CNSL) and to investigate the fluid flow behaviour under the influence of temperature since the fluid properties like viscosity and density have strong dependence on temperature. The CNSL containing 60–65 % anacardic acid was decarboxylated to produce cardanol and CO2at wall temperatures ranging between 393 K and 433 K, respectively. The characteristics of the CNSL, essentially a non-Newtonian fluid, was analysed at different temperatures and its rheological behaviour was studied using the well-known power law model. It was observed that CNSL follows a pseudoplastic behaviour and its viscosity, along with the liquid residence time, was found to decrease till 413 K, while a further increase in temperature resulted in product degradation due to charring, accompanied by an increase in viscosity and residence time. Using measured values for the viscosity, the film thickness was calculated for each wall temperature within the 393–433 K temperature range, showing an increase of the film thickness with temperature and viscosity. Computational Fluid Dynamics (CFD) studies were carried out for the first time for this reactor configuration, using the volume of fluid (VOF) model for the reactive flow. The results obtained from these simulations were in concurrence with the experimental outcomes: velocity profiles along the length of the reactor show its highest values at a wall temperature of 413 K, while lower velocity values were observed when the temperatures were lower or greater than 413 K.

Computationally Efficient Modelling of Oil Jet-Breakup and Film Formation for Bearing Chamber Applications

2018 ◽  
Author(s):  
Jee Loong Hee ◽  
Kathy Simmons ◽  
Bruce Kakimpa ◽  
David Hann
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Film Formation ◽  
Viscous Sublayer ◽  
Current Data ◽  
Turbulent Dispersion ◽  
Research Centre ◽  
Shear Stresses ◽  
Two Phase ◽  
Injection Point

In previously published experimental work completed at the Gas Turbine and Transmissions Research Centre (G2TRC), oil fed to an aeroengine location bearing via underrace feed was seen to shed from the cage, forming a film on static surfaces near the bearing and subsequently shedding into the bearing chamber. A high-fidelity computational model of the two-phase flow in an aeroengine bearing chamber must adequately reproduce such behaviour but there are significant challenges in modelling both the oil breakup after shedding and the subsequent film formation. It is very computationally costly to resolve an oil film interface using the Volume of Fluid (VOF) approach at regions of thin film and it is unacceptably inaccurate to resolve thick film using an explicit thin film modelling technique such as the Eulerian Thin Film Model (ETFM). A proposed solution is to couple together VOF, ETFM and discrete phase modelling (DPM). Previously published G2TRC work shows how VOF and ETFM can be successfully coupled. This paper investigates the coupling of ETFM and DPM. The evaluation of film momentum transport and air-particle momentum transfer/Lagrangian particle tracking are studied using a low Reynolds number turbulence model. Validation is required to ensure that these models work together as intended. To this end a preliminary CFD study was carried out on a published case investigated experimentally and computationally in which a jet is injected into a duct via a nozzle, breaking up into droplets before forming a wall film. The droplets are produced by primary atomization due to liquid instabilities at the injection point. Secondary breakup occurs due to surface instabilities prompted by the high-velocity cross-flow. Small droplets are transported downstream whereas larger droplets deflect minimally hitting the wall and forming a thin film. In the work presented here quantitative film thickness data from experiments and prior simulations are compared to current data. The success of the simulation is found to depend on shear-transportation, turbulent dispersion of the particles, particle grouping, mass transportation as well as accurate prediction of interfacial shear-stresses. With suitable modelling parameters it was possible to predict film thickness to within 28.9% of those seen experimentally. The present ETFM-DPM modelling showed improvements over previously published models in prediction of shear-stresses and film transportation as the ω-equation could be integrated through the viscous sublayer. The developed approach is now mature enough to be applied to the bearing chamber geometry investigated experimentally at G2TRC and this is proposed for future work.

Numerical and Experimental Study for Unsteady Oil Film Thickness of the Rotating Cylinder Chamber Wall

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Zhao Jingyu ◽  
Liu Zhenxia
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Film Thickness ◽  
Rotation Speed ◽  
Film Formation ◽  
Rotating Cylinder ◽  
Chamber Wall ◽  
Wall Heat Transfer ◽  
Oil Film ◽  
Oil Flow

The oil film thickness on the bearing chamber wall directly affects the wall heat transfer efficiency, so a fundamental study on the motion of oil film on the rotating cylinder has been conducted to this end. On the one hand, the rotating cylinder test rig was designed, and an ultrasonic measurement system was established to measure the dynamic oil film thickness. On the other hand, the unsteady oil film heat and mass transfer movement model was also established, and the numerical simulation to solve oil film motion by using computational fluid dynamic (CFD) commercial software was carried out. Meanwhile, on the basis of study on the oil film formation process and film thickness verification, the oil film distributions on the chamber wall with rotation speed and oil flow rate were analyzed and studied. Results show that the oil film on the rotating chamber wall experiences a development process from the oil film formation to basic stability, about 1.0 s in this paper. And comparison between the numerical and experimental data shows that the maximum error between experimental data and numerical simulation is 7.76%. Moreover, for the oil film distributions in the stable state, oil film thickness shows a trend of decreasing with the increasing of rotation speed, but increasing with the increasing of oil flow rate. The research here will provide the basis for subsequent study of the interaction between oil film motion and the wall heat transfer.

Organic thin film thickness-dependent photocurrents polarity in graphene heterojunction phototransistor

Carbon ◽  
2021 ◽  
Vol 178 ◽  
pp. 506-514
Author(s):  
Meiyu He ◽  
Jiayue Han ◽  
Xingwei Han ◽  
Jun Gou ◽  
Ming Yang ◽  
...  
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Organic Thin Film ◽  
Thin Film Thickness

scholarly journals Experimental Study on the Thickness-Dependent Hardness of SiO2 Thin Films Using Nanoindentation

Coatings ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 23
Author(s):  
Weiguang Zhang ◽  
Jijun Li ◽  
Yongming Xing ◽  
Xiaomeng Nie ◽  
Fengchao Lang ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Grain Size ◽  
Integrated Circuits ◽  
Film Thickness ◽  
Depth Range ◽  
Micro Electro Mechanical Systems ◽  
Si Substrates ◽  
Sio2 Thin Film ◽  
Average Grain Size

SiO2 thin films are widely used in micro-electro-mechanical systems, integrated circuits and optical thin film devices. Tremendous efforts have been devoted to studying the preparation technology and optical properties of SiO2 thin films, but little attention has been paid to their mechanical properties. Herein, the surface morphology of the 500-nm-thick, 1000-nm-thick and 2000-nm-thick SiO2 thin films on the Si substrates was observed by atomic force microscopy. The hardnesses of the three SiO2 thin films with different thicknesses were investigated by nanoindentation technique, and the dependence of the hardness of the SiO2 thin film with its thickness was analyzed. The results showed that the average grain size of SiO2 thin film increased with increasing film thickness. For the three SiO2 thin films with different thicknesses, the same relative penetration depth range of ~0.4–0.5 existed, above which the intrinsic hardness without substrate influence can be determined. The average intrinsic hardness of the SiO2 thin film decreased with the increasing film thickness and average grain size, which showed the similar trend with the Hall-Petch type relationship.

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