A numerical method for the prediction of combustion instabilities

This thesis describes one of the first computational works to investigate the physical feedback mechanisms associated with self-excited, combustion-driven instabilities in gas turbines. For this purpose, a novel numerical method based on large eddy simulation is devised. The method (called BOFFIN) uses a fully compressible formulation to account for acoustic wave propagation and applies a transported probability density function approach for turbulence-chemistry interactions. The latter is solved by the Eulerian stochastic fields method and is complemented by two different 15-step / 19 species chemical reaction schemes. This approach is shown to be flame burning regime independent and therefore highly applicable in the context of partially premixed gas turbine combustion. Combustion instabilities are a phenomenon often encountered in the late design stages of modern gas turbine combustors. Under certain conditions, these types of instabilities can develop into sustained limit-cycle oscillations with potentially severe consequences on a combustor's operating behaviour. In order to study the various physical feedback mechanisms driving such limit-cycle oscillations, two different test cases are simulated in the present work. Firstly, the combined effects of thermo-acoustic and hydrodynamic instabilities are examined in the lab-scale PRECCINSTA model combustor. Secondly, the superposition of a longitudinal and azimuthally spinning instability mode is investigated in the industrial SGT-100 combustor. Amongst the different feedback mechanisms identified and studied in these cases are: mass flow rate and equivalence ratio oscillations, as well as hydrodynamic phenomena such as flame angle oscillations, periodic vortex shedding and a precessing vortex core. It is further demonstrated that in addition to reproducing longitudinal instability modes, the applied LES approach is capable of accounting for modes acting in the transverse direction. Overall, the findings of this research project strongly suggest that BOFFIN is a reliable and accurate method for the prediction of self-excited combustion instabilities in gas turbines.Open Acces

Maine EPSCoR, vol. 1, issue 1

The University of Maine recently gained Carnegie R1 status, a level of recognition that speaks to the quality and scale of research happening at Maine’s land grant, sea grant, and space grant institution, and across the state as a whole. Research institutes, centers and labs established because of NSF EPSCoR RII Track-1 grants have created a significant and lasting impact in Maine. These entities include the Advanced Structures and Composites Center, Frontier Institute for Research in Sensor Technologies, Forest Bioproducts Research Institute, and Mitchell Center for Sustainability Solutions, which have generated over 500 million dollars in new R&D funding for the state following the completion of their RII Track-1 support. Maine EPSCoR’s current NSF EPSCoR RII Track-1 grant, Maine-eDNA, is set to embark on a full field season with work occurring throughout the state. We recognize the researchers, staff, graduate students, and undergraduate students who continue to actively participate in this work. Their effort and resilience in the face of uncertain and changing circumstances is inspiring and makes real contributions in our efforts to expand educational opportunities in STEM, drive workforce development, and strengthen research capacity in the state of Maine

The Alberta Heart Failure Etiology and Analysis Research Team (HEART) study

Background Nationally, symptomatic heart failure affects 1.5-2% of Canadians, incurs $3 billion in hospital costs annually and the global burden is expected to double in the next 1–2 decades. The current one-year mortality rate after diagnosis of heart failure remains high at >25%. Consequently, new therapeutic strategies need to be developed for this debilitating condition. Methods/Design The objective of the Alberta HEART program (http://albertaheartresearch.ca) is to develop novel diagnostic, therapeutic and prognostic approaches to patients with heart failure with preserved ejection fraction. We hypothesize that novel imaging techniques and biomarkers will aid in describing heart failure with preserved ejection fraction. Furthermore, the development of new diagnostic criteria will allow us to: 1) better define risk factors associated with heart failure with preserved ejection fraction; 2) elucidate clinical, cellular and molecular mechanisms involved with the development and progression of heart failure with preserved ejection fraction; 3) design and test new therapeutic strategies for patients with heart failure with preserved ejection fraction. Additionally, Alberta HEART provides training and education for enhancing translational medicine, knowledge translation and clinical practice in heart failure. This is a prospective observational cohort study of patients with, or at risk for, heart failure. Patients will have sequential testing including quality of life and clinical outcomes over 12 months. After that time, study participants will be passively followed via linkage to external administrative databases. Clinical outcomes of interest include death, hospitalization, emergency department visits, physician resource use and/or heart transplant. Patients will be followed for a total of 5 years. Discussion Alberta HEART has the primary objective to define new diagnostic criteria for patients with heart failure with preserved ejection fraction. New criteria will allow for targeted therapies, diagnostic tests and further understanding of the patients, both at-risk for and with heart failure

Modelling of soot and NOx emission from a lean azimuthal flame (LEAF) aeronautical model combustor using incompletely stirred reactors

A lean azimuthal flame (LEAF) combustor fuelled with Jet-A1 is numerically simulated. The LEAF concept, motivated by the ``flameless'' oxidation principle, is based on azimuthally arranged fuel sprays and opposed injections of air in an axisymmetric chamber with a central outlet. This unique mixing configuration results in a highly turbulent toroidal reaction zone and achieves ultra-low emissions, making it attractive for future aero-engines. In this work, Incompletely Stirred Reactor (ISR) theory is employed to assess its capability in predicting the experimentally measured NOx concentration and soot particle size distribution (PSD) at the exhaust. Detailed fuel pyrolysis and oxidation chemistry, NOx formation models, and a detailed physicochemical sectional soot model are employed and solved in a post-processing fashion, leveraging a RANS/flamelet simulation with simple chemistry of a condition with thermal power of 20 kW. It is found that pollutant formation can be well reproduced in this burner, provided that an accurate energy balance is available to quantify the heat loss through the water-cooled aluminium frame and the air-cooled quartz windows present in the experiments. A parametric analysis showed that a departure from the adiabatic condition by even a few hundred W could substantially improve the agreement with measurements. In particular, heat losses were found to be responsible for a significant reduction in NOx emission, affected primarily by NNH and N2O routes, and an increase in soot emission at the burner exit, influenced mainly by finite-rate soot oxidation. Equivalently, it may be concluded that using realistic walls in the experiments, such as ceramic coatings that better reflect aviation gas turbines, would result in lower soot emission but higher NO emission. In this direction, the ISR approach and network approaches based on ISRs may be employed for preliminary evaluations and to identify suitable mixing patterns and residence times that ensure low pollutant formation across a wide operating range.This project received funding from the European Union’s Horizon 2020 research and innovation program under the Center of Excellence in Combustion (CoEC) project, grant agreement No 952181 and the Clean Sky 2 Joint Undertaking (JU) under grant agreement 831804, project LEAFINNOX. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and the Clean Sky 2 JU members other than the Union

Large Eddy Simulation of a Reacting Kerosene Spray in Hot Vitiated Cross-Flow

The evaporation and combustion characteristics of a kerosene spray injected perpendicularly into a cross-flow of high-temperature vitiated air is investigated. This fundamental flow configuration has wider implications for the future development of ultra-low emission aeronautical combustors, particularly with respect to technologies involving MILD combustion. Large eddy simulations with a Eulerian-Lagrangian framework are performed to investigate the spray evolution and the characteristics of the reaction zone for a range of conditions. For the closure of turbulence-chemistry interactions at the sub-grid scales, a transported probability density function approach solved by the Eulerian stochastic fields method is applied. A configuration based on the use of airblast atomisation is assessed first and compared with experimental observations. The effect of the atomiser air-to-liquid mass flow ratio is studied in greater detail, both in terms of the resulting gas-phase properties and the droplet evaporation process. Then, the effect of ambient pressure on the global spray flame behaviour is examined. For this part of the study, no atomising air is included in the simulation to separate the effects of ambient pressure on the spray from the interaction with the air jet. Analysis of the flame and spray properties at cross-flow operating pressures of 1 atm, 2 bar and 4 bar highlights the strong coupling between the reacting flow and droplet evaporation characteristics, which are highly affected by the penetration of the spray into a flow field characterised by relatively large gradients of temperature. The results reported in this work provide fundamental understanding for the development of novel low-emission combustion technologies and demonstrate the feasibility of applying large eddy simulation with detailed chemistry for the investigation of reacting aviation fuel sprays in hot vitiated cross-flow.ISSN:1386-6184ISSN:1573-198

Is there an association between spatial accessibility of outpatient care and utilization? Analysis of gynecological and general care

Abstract Background In rural regions with a low population density, distances to health care providers as well as insufficient public transport may be barriers for the accessibility of health care. In this analysis it was examined whether the accessibility of gynecologists and GPs, measured as travel time both by car and public transport has an influence on the utilization of health care in the rural region of Western Pomerania in Northern Germany. Methods Utilization data was obtained from the population based Study of Health in Pomerania (SHIP). Utilization was operationalized by the parameter “at least one physician visit during the last 12 months”. To determine travel times by car and by public transport, network analyses were conducted in a Geographic Information System (GIS). Multivariate logistic regression models were calculated to identify determinants for the utilization of gynecologists and GPs. Results There is no significant association between the accessibility by car or public transport and the utilization of gynecologists and GPs. Significant predictors for the utilization of gynecologists in the regression model including public transport are age (OR 0.960, 95% CI 0.950–0.971, p < 0.0001), social class (OR 1.137, 95% CI 1.084–1.193, p < 0.0001) and having persons ≥18 years in the household (OR 2.315, 95% CI 1.116–4.800, p = 0.0241). Conclusions In the examined region less utilization of gynecologists is not explainable with long travel times by car or public transport

Investigation of high density gradients flows by pulsed digital holographic interferometry

International audienc