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

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

Evaluation of a volume of fluid CFD methodology for the oil film thickness estimation in an aero-engine bearing chamber

The presented work aims to identify a Volume of Fluid (VOF) CFD approach for the transient simulation of air/oil flows inside an aero-engine bearing chamber. Typically VOF requires relatively fine grids and consequently small time-steps to sufficiently resolve the formation of oil films and their interaction with air flows. The need to achieve a stationary-state which requires flow times on the order of seconds makes the compromise between simulation accuracy and simulation times a challenging choice when using the VOF method. In this work, the use of the Compressive Interface Reconstruction scheme with bounded second order implicit time discretization has enabled a significant speed-up of the simulation times against the previously adopted explicit Geometric-Reconstruction scheme. The results are evaluated against experimental data available in the literature

Economic consequences of investing in anti-HCV antiviral treatment from the Italian NHS perspective : a real-world-based analysis of PITER data

OBJECTIVE: We estimated the cost consequence of Italian National Health System (NHS) investment in direct-acting antiviral (DAA) therapy according to hepatitis C virus (HCV) treatment access policies in Italy. METHODS: A multistate, 20-year time horizon Markov model of HCV liver disease progression was developed. Fibrosis stage, age and genotype distributions were derived from the Italian Platform for the Study of Viral Hepatitis Therapies (PITER) cohort. The treatment efficacy, disease progression probabilities and direct costs in each health state were obtained from the literature. The break-even point in time (BPT) was defined as the period of time required for the cumulative costs saved to recover the Italian NHS investment in DAA treatment. Three different PITER enrolment periods, which covered the full DAA access evolution in Italy, were considered. RESULTS: The disease stages of 2657 patients who consecutively underwent DAA therapy from January 2015 to December 2017 at 30 PITER clinical centres were standardized for 1000 patients. The investment in DAAs was considered to equal €25 million, €15 million, and €9 million in 2015, 2016, and 2017, respectively. For patients treated in 2015, the BPT was not achieved, because of the disease severity of the treated patients and high DAA prices. For 2016 and 2017, the estimated BPTs were 6.6 and 6.2 years, respectively. The total cost savings after 20 years were €50.13 and €55.50 million for 1000 patients treated in 2016 and 2017, respectively. CONCLUSIONS: This study may be a useful tool for public decision makers to understand how HCV clinical and epidemiological profiles influence the economic burden of HCV

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

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

Progettazione preliminare di una turbina di bassa pressione per un nuovo motore di tipo intercooled turbofan

Una nuova configurazione di motore turbofan per aeromobili a lungo raggio è attualmente in fase di studio. Il modello include un accoppiamento con riduttore di velocità tra turbina di bassa o media pressione (LPT o IPT) e ventola, intercoolers ed un’inversione della direzione del flusso del gas nel motore (reverse-flow core). In questa tesi si è realizzata la progettazione preliminare delle turbine LP ed IP nelle configurazioni a due o tre alberi, per valutarne i potenziali vantagg

Evaluation of a volume of fluid CFD methodology for the oil film thickness estimation in an aero-engine bearing chamber

The presented work aims to identify a Volume of Fluid (VOF) CFD approach for the transient simulation of air/oil flows inside an aero-engine bearing chamber. Typically VOF requires relatively fine grids and consequently small time-steps to sufficiently resolve the formation of oil films and their interaction with air flows. The need to achieve a stationary-state which requires flow times on the order of seconds makes the compromise between simulation accuracy and simulation times a challenging choice when using the VOF method. In this work, the use of the Compressive Interface Reconstruction scheme with bounded second order implicit time discretization has enabled a significant speed-up of the simulation times against the previously adopted explicit Geometric-Reconstruction scheme. The results are evaluated against experimental data available in the literature

Territori post metropolitani ed effetti della crisi nell’area centrale veneta

L’economia italiana sta attraversando la peggiore recessione, per intensità e durata, dal dopoguerra. Anche nell’area centrale ve-neta la crisi sta facendo emergere una nuova domanda di governo del territorio, non più legata ad una fase espansiva, bensì al proble-ma delle possibili destinazioni d’uso di strutture produttive, com-merciali e per il tempo libero abbandonate, della limitazione della crescita edilizia e, più in generale, della transizione verso nuovi mo-delli di sviluppo. Anche se alcuni fenomeni legati a ristrutturazioni aziendali, ri-articolazioni di fasi produttive e delocalizzazioni erano già in atto in epoca pre-crisi, le dismissioni più recenti hanno avuto effetti più visibili e dirompenti. Sono emerse nuove domande: le interminabili distese di capannoni industriali di medio-piccola ta-glia possono essere assunte come possibili indicatori di transizione verso fenomeni post-metropolitani? Queste tendenze si presenta-no come effetti locali di fenomeni globali, partecipano ad un pro-cesso di scale-making determinando cambiamenti di gravitazioni, riarticolazione di assetti gerarchici; decadenza di polarità; forme fi-siche indeterminate, minore qualità degli spazi urbani e territoriali. Il contributo riprende alcune riflessioni sul caso studio di Villorba in provincia di Treviso nell’ambito delle attività di ricerca svolte dal gruppo dell’unità di ricerca dell’Università IUAV di Venezia del PRIN “Territori post-metropolitani come forme urbane emergenti: le sfide della sostenibilità, abitabilità e governabilità”2

Corrigendum to \u201cPremature ovarian senescence and a high miscarriage rate impair fertility in women with HCV\u201d [J Hepatol 68 (2018) 33\u201341](S0168827817322596)(10.1016/j.jhep.2017.08.019)

It has come to our attention that the PITER framework investigator, Alessandro Federico, was incorrectly listed as F. Alessandro in the original manuscript. Please note that the correct name of this author is Alessandro Federico (2nd University of Naples). The correct list of PITER investigators is in the footnote below

Premature ovarian senescence and a high miscarriage rate impair fertility in women with HCV

Premenopausal women who are HCV positive (HCV+) have failing ovarian function, which is likely to impact their fertility. Thus, we investigated the reproductive history, risk of infertility, and pregnancy outcomes in women of childbearing age who were HCV+