A coupled Lagrangian-Eulerian framework to model droplet to film interaction with heat transfer

A droplet to film interaction modelling Computational Fluid Dynamics (CFD) technique is presented in this work. The eventual target application is an aeroengine bearing chamber where oil is used to lubricate and cool the bearings and the bearing chamber walls. Inside the chamber, the oil is found as jets/filaments, film and as droplets in the highly rotational environment. Of particular interest in this work is the formation of the continuous film from the droplets. Spray-film is another relevant application with droplets forming film as it cools the wall. In this work, the liquid and gas continua are modelled using an enhanced Volume of Fluid (VoF) technique. The droplets in the core-air are tracked using a Lagrangian framework that treats them as discrete particles and are coupled to the Eulerian VoF film upon impact using source terms. In finite volume CFD techniques, a prohibitively large number of computational cells would be required to describe, in details, the droplet-film impact phenomenon. The proposal here is that finer mesh, sufficient to capture the film physics, is used only close to walls or where film is expected to form. Simple droplet train to complex spray-film setups are used to verify and validate for mass, momentum and energy transfer. The technique was also applied to experimental rigs representative of aeroengine bearing chambers; and as with every CFD problems, the choice of boundary conditions determines the final output. A parametric study of the bearing chamber flows shows that film thickness increases with flow rate. The film thickness increases with a reducing shaft speed for same flow rate. The heat transfer coefficient results show that higher flow rates provide better heat transfer at higher shaft speeds

A coupled Lagrangian-Eulerian framework to model droplet to film interaction with heat transfer

A droplet to film interaction modelling Computational Fluid Dynamics (CFD) technique is presented in this work. The eventual target application is an aeroengine bearing chamber where oil is used to lubricate and cool the bearings and the bearing chamber walls. Inside the chamber, the oil is found as jets/filaments, film and as droplets in the highly rotational environment. Of particular interest in this work is the formation of the continuous film from the droplets. Spray-film is another relevant application with droplets forming film as it cools the wall. In this work, the liquid and gas continua are modelled using an enhanced Volume of Fluid (VoF) technique. The droplets in the core-air are tracked using a Lagrangian framework that treats them as discrete particles and are coupled to the Eulerian VoF film upon impact using source terms. In finite volume CFD techniques, a prohibitively large number of computational cells would be required to describe, in details, the droplet-film impact phenomenon. The proposal here is that finer mesh, sufficient to capture the film physics, is used only close to walls or where film is expected to form. Simple droplet train to complex spray-film setups are used to verify and validate for mass, momentum and energy transfer. The technique was also applied to experimental rigs representative of aeroengine bearing chambers; and as with every CFD problems, the choice of boundary conditions determines the final output. A parametric study of the bearing chamber flows shows that film thickness increases with flow rate. The film thickness increases with a reducing shaft speed for same flow rate. The heat transfer coefficient results show that higher flow rates provide better heat transfer at higher shaft speeds

A Computational Fluid Dynamics Simulation of Oil–Air Flow Between the Cage and Inner Race of an Aero-engine Bearing

In aeroengines the shafts are supported on bearings that carry the radial and axial loads. A ball bearing is made up of an inner-race, an outer-race and a cage which contains the balls, these together comprise the bearing elements. The bearings require oil for lubrication and cooling. The design of the bearing studied in this work is such that the oil is fed to the bearing through holes/slots in the inner race. At each axial feed location the oil is fed through a number of equispaced feedholes/slots but there is a different number of holes at each location. Once the oil has passed through the bearing it sheds outwards from both sides into compartments known as the bearing chambers. A number of studies have been carried out on the dynamics of bearings. Most of the analyses consider the contributions of fluid forces as small relative to the interaction of the bearing elements. One of the most sophisticated models for a cage-raceway analysis is based on the work of Ashmore et al. [1], where the cage-raceway is considered to be a short journal bearing divided into sectors by the oil feeds. It is further assumed that the oil exits from the holes and forms a continuous block of oil that exits outwards on both sides of the cage-raceway. In the model, the Reynolds equation is used to estimate the oil dynamics. Of interest in this current work is the behaviour of the oil and air within the space bounded by the cage and inner race. The aim is to determine whether oil feed to the bearing can be modelled as coming from a continuous slot or if the discrete entry points must be modelled. A Volume of Fluid Computational Fluid Dynamics approach is applied. A sector of a ball bearing is modelled with a fine mesh and the detailed simulations show the flow behaviour for different oil splits to the three feed locations of the bearing thus providing information useful to understanding oil shedding into the bearing chambers. The work shows that different flow behaviour is predicted by models where the oil inlets through a continuous slot compared to discrete entry holes. The form and speed of oil shedding from the bearing is found to depend strongly on shaft speed with the shedding speed being slightly higher than the cage linear speed. The break-up pattern of oil on the cage inner surface suggests smaller droplets will be shed at higher shaft speed

A Coupled Euler-Lagrange CFD Modelling of Droplets-To-Film

In this paper, a droplet to film interaction model technique is presented. In the proposed approach, the liquid and gas continua are modelled using an enhanced Volume of Fluid (VoF) technique while the droplets are tracked using a Lagrangian framework and are coupled to the Eulerian phases using source terms. The eventual target application is an aeroengine bearing chamber in which oil is found as droplets, shed from the bearings, splashing on impact, separated from wall surfaces at obstacles or simply re-entrained, and as a continuum oil film coating the bearing chamber outer walls which it also cools. In finite volume CFD techniques, a prohibitively large number of cells would be required to describe the details of the droplet impact phenomenon. Based on published correlations, the splashing droplets are created and tracked as Lagrangian particles. The flowing film and the gas continua are handled with an enhanced Volume of Fluid technique

Female reproductive tract infections: understandings and care seeking behaviour among women of reproductive age in Lagos, Nigeria

<p>Abstract</p> <p>Background</p> <p>Reproductive tract infections (RTI's) are endemic in developing countries and entail a heavy toll on women. If untreated, RTI's can lead to adverse health outcomes such as infertility, ectopic pregnancy and increased vulnerability to transmission of the human immunodeficiency virus. It is also associated with adverse pregnancy outcomes. While RTI's and its sequelae abound in Nigeria, there is paucity of publications on the subject in the country. This study assessed the understandings and care seeking behavior with regards to RTI's among women of reproductive age in Lagos, Nigeria with the aim of improving awareness on the subject.</p> <p>Methods</p> <p>A descriptive cross sectional survey of women attending the gynaecological outpatient and family planning clinics of the Lagos State University Teaching Hospital was carried out between 1^stJune 2008 and 31^stAugust 2008 using a pre-tested questionnaire. Data was analysed using the Epi-Info 3.5 statistical software of the Centre for Disease Control and Prevention, Atlanta U.S.A.</p> <p>Results</p> <p>Most of the respondents (77.2%) had heard of RTI's. Toilet was the most perceived mode of contracting RTI's (44.6%), followed by sexual intercourse and poor hygiene. Vaginal discharge was the commonest symptom of RTI's named while inability to get pregnant was the commonest named complication. Majority of the respondent's demonstrated poor overall knowledge of symptoms and complications of RTI"s. 37.4% of the respondents had experienced symptoms of RTI's in the preceding six months. Vaginal discharge was the commonest symptom reported (21.8%) and the majority of those who reported symptoms sought medical treatment. Government health centres were the most visited health facilities for treatment.</p> <p>Conclusion</p> <p>Even though most of the respondents have heard of RTI's and sought treatment when symptomatic, they demonstrated poor overall understanding of the subject. There is need to educate women on preventive strategies, as RTI's are often assymptomatic.</p

The global burden of cancer attributable to risk factors, 2010-19 : a systematic analysis for the Global Burden of Disease Study 2019

Background Understanding the magnitude of cancer burden attributable to potentially modifiable risk factors is crucial for development of effective prevention and mitigation strategies. We analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 to inform cancer control planning efforts globally. Methods The GBD 2019 comparative risk assessment framework was used to estimate cancer burden attributable to behavioural, environmental and occupational, and metabolic risk factors. A total of 82 risk-outcome pairs were included on the basis of the World Cancer Research Fund criteria. Estimated cancer deaths and disability-adjusted life-years (DALYs) in 2019 and change in these measures between 2010 and 2019 are presented. Findings Globally, in 2019, the risk factors included in this analysis accounted for 4.45 million (95% uncertainty interval 4.01-4.94) deaths and 105 million (95.0-116) DALYs for both sexes combined, representing 44.4% (41.3-48.4) of all cancer deaths and 42.0% (39.1-45.6) of all DALYs. There were 2.88 million (2.60-3.18) risk-attributable cancer deaths in males (50.6% [47.8-54.1] of all male cancer deaths) and 1.58 million (1.36-1.84) risk-attributable cancer deaths in females (36.3% [32.5-41.3] of all female cancer deaths). The leading risk factors at the most detailed level globally for risk-attributable cancer deaths and DALYs in 2019 for both sexes combined were smoking, followed by alcohol use and high BMI. Risk-attributable cancer burden varied by world region and Socio-demographic Index (SDI), with smoking, unsafe sex, and alcohol use being the three leading risk factors for risk-attributable cancer DALYs in low SDI locations in 2019, whereas DALYs in high SDI locations mirrored the top three global risk factor rankings. From 2010 to 2019, global risk-attributable cancer deaths increased by 20.4% (12.6-28.4) and DALYs by 16.8% (8.8-25.0), with the greatest percentage increase in metabolic risks (34.7% [27.9-42.8] and 33.3% [25.8-42.0]). Interpretation The leading risk factors contributing to global cancer burden in 2019 were behavioural, whereas metabolic risk factors saw the largest increases between 2010 and 2019. Reducing exposure to these modifiable risk factors would decrease cancer mortality and DALY rates worldwide, and policies should be tailored appropriately to local cancer risk factor burden. Copyright (C) 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license.Peer reviewe

Performance and Emission Characteristics of Heptane/Toluene Blends at Constant Injection Operation on a CI Engine

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