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A diagnostic method for gas-path faults of turbofan engines, relying on a Probabilistic Neural Network (PNN) coupled with a thermodynamic model of the engine, is presented. The novel aspect of the method is that its training information is generated dynamically by an accompanying Engine Performance Model. In the proposed approach, the PNN efficiently addresses the first step of a diagnostic process (i.e., detection of the faulty component at the current operating point), while with the aid of an adaptive engine model, the fault is then further isolated and identified. A description of the proposed method and training aspects of the PNN are presented. The method is applied to the case of a mixed-flow turbofan engine to diagnose common gas-path faults in compressors and turbines (i.e., fouling, FOD, erosion, and tip clearance). Its performance is evaluated using realistic fault data that may be acquired at various operating conditions within a flight envelope.

Background: Despite recent guidelines appropriate lipid-lowering treatment (LLT) remains suboptimal in everyday clinical practice. Aims: We aimed to describe clinical practice of use of LLT for at least high CV risk populations in a Hellenic real-world setting and assess how this relates to the European Society of Cardiology treatment guidelines. Methods: We analyzed data from a retrospective cohort study of the National Registry of patients with dyslipidemia between 1/7/2017 and 30/6/2019 who were at least of high CV risk and filled a dual or triple lipid-lowering treatment (dLLT, tLLT) prescription. The primary outcomes of interest of this analysis were to report on the patterns of LLT use in at least high CV risk patients. Results: A total of 994,255 (45.4% of Greeks on LLT) were of at least high CV risk and 120,490 (5.5%) were on dLLT or tLLT. The percentage of patients with reported statin intolerance ranged from 2 to 10%. While persistence was reported to be satisfactory (>85% for both dLLT or tLLT), adherence was low (ranging between 14 and 34% for dLLT). In 6-month intervals, the percentage of patients achieving a low-density lipoprotein cholesterol (LDL-C) target below 100 md/dL ranged from 20% to 23% for dLLT and 34%–37% for tLLT. Conclusions: The prevalence of at least high CV risk patients among patients receiving LLT in Greece is substantial. Despite the high persistence and probably due to the low adherence to treatment, LDL-C remains above targets in more than two thirds of patients.

A review of existing research on signatures of gas turbine faults is presented. Faults that influence the aerothermodynamic performance of compressors and turbines, such as fouling, tip clearance increase, erosion, variable geometry system malfunction, and object impact damage, are covered. The signatures of such faults, which are necessary for establishing efficient gas path diagnostic methods, are studied. They are expressed through mass flow capacity and efficiency deviations. The key characteristics of the ratio of such deviations are investigated in terms of knowledge existing in published research. Research based on experimental studies, field data, and results of detailed fluid dynamic computations that exist today is found to provide such information. It is shown that although such signatures may be believed to have a unique correspondence to the type of component fault, this is only true when a particular engine and fault type are considered. The choice of diagnostic methods by developers should, thus, be guided by such considerations instead of using values taken from the literature without considering the features of the problem at hand.

Data from the steady-state operation of gas turbine engines are used in gas path diagnostic procedures. A method to identify steady-state operation is thus required. This paper initially explains and demonstrates the factors that cause a deviation in engine health when transient data are used for diagnosis and shows that there is a threshold in the slope of time traces, below which the variation in engine health parameters is acceptable. A methodology for deriving a criterion for steady-state operation based on actual flight data is then presented. The slope of the exhaust gas temperature variation with time and the size of its time-series window, from which this slope is determined, are the required parameters that must be specified when applying this criterion. It is found that the values of these parameters must be selected so that a sufficient number of steady-state points are available without compromising the accuracy of the diagnostic procedure.

In a time when low emission solutions and technologies are of utmost importance regarding the sustainability of the aviation sector, this publication introduces a reduced-order physics-based model for combustion chambers of aeroengines, which is capable of reliably producing accurate pollutant emission and combustion efficiency estimations. The burner is subdivided into three volumes, with each represented by a single perfectly stirred reactor, thereby resulting in a simplified three-element serial chemical reactor network configuration, reducing complexity, and promoting the generality and ease of use of the model, without requiring the proprietary engine information needed by other such models. A tuning method is proposed to circumvent the limitations of its simplified configuration and the lack of detailed geometric data for combustors in literature. In contrast to most similar frameworks, this also provides the model with the ability to simultaneously predict the combustion efficiency and all pollutant emissions of interest (NOx, CO and unburnt hydrocarbons) more effectively by means of implementing a detailed chemical kinetics model. Validation against three correlation methods and actual aeroengine configurations demonstrates accurate performance and emission trend predictions. Integrated within two distinct combustion chamber low-emission preliminary design processes, the proposed model evaluates each new design, thereby displaying the ability to be employed in terms of optimizing a combustor’s overall performance given its sensitivity to geometric changes. Overall, the proposed model proves its worth as a reliable and valuable tool for use towards a greener future in aviation.

An approach for preliminary aero-engine design, incorporating a mean-line code for the design of axial-flow, multi-stage compressors, is presented. The compressor mean-line code is developed and integrated within a framework for the preliminary design and assessment of aero-engine concepts. It is then combined with modules for compressor map generation, multi-point engine design, steady-state and transient engine off-design performance and aircraft mission analysis. Implementation examples are presented, demonstrating the determination of the optimal combination of compressor and engine design parameters for achieving minimum fuel burn over a specific aircraft mission, while obeying constraints that guarantee operability over the entire flight envelope. Constraints related to compressor stability during transient maneuvers between idle and static take-off conditions and engine temperature limits at maximum take-off are respected by the final design. The results demonstrate the potential for design trade-offs between engine performance at the aircraft mission level and compressor aerodynamic stability.

Disks in gas turbines are optimized for minimum weight, while satisfying both geometry and stress constraints, in order to minimize the engine production, operation, and maintenance costs. In the present paper, a tool is described for the preliminary mechanical design of gas turbine disks. A novel formulation is presented, where the disk weight minimization is achieved by maximizing the stresses developed in the disk. The latter are expressed in the form of appropriately defined design and burst margins. The computational capabilities of the tool developed are demonstrated through comparisons to calculations with a higher fidelity tool. The importance of accurately calculating thermal stresses is demonstrated and the ability of the tool for such calculations is discussed. The potential and efficiency of the tool are illustrated through a proposed re-design of the disks of a well-documented ten-stage compressor. Finally, the integration of the tool into an overall engine design framework is discussed.

Objectives Depression and anxiety are linked bi-directionally with inflammatory rheumatic diseases (IRDs) activity, which in turn, depends on subjective patient reported outcomes that can be distorted by comorbid mood disorders. We tested the hypothesis that introduction and/or switching of biologic agents for IRDs are associated with treatment for depression and/or anxiety, by analysing real-world data.Methods Using a country-wide electronic prescription database (10 012 604 registered, 99% population coverage), we captured almost all patients with rheumatoid arthritis (n=12 002), psoriatic arthritis (n=5465) and ankylosing spondylitis (n=6423) who received biologic disease modifying anti-rheumatic drugs (bDMARDs) during a 2-year period (8/2016–7/2018). Concomitant antidepressant/anxiolytic medication use was documented in patients who started or switched bDMARDs and compared with those who remained on conventional synthetic (cs)DMARDs or the same bDMARD, respectively, by multivariate regression analysis.Results Two-year data analysis on 42 815 patients revealed that bDMARD introduction was associated with both antidepressant [OR: 1.248, 95% CI 1.153 to 1.350, p

This paper presents a modular, flexible, extendable and fast-computational framework that implements a multidisciplinary, varying fidelity, multi-system approach for the conceptual and preliminary design of novel aero-engines. In its current status, the framework includes modules for multi-point steady-state engine design, aerodynamic design, engine geometry and weight, aircraft mission analysis, Nitrogen Oxide (NOx) emissions, control system design and integrated controller-engine transient-performance analysis. All the modules have been developed in the same software environment, ensuring consistent and transparent modeling while facilitating code maintainability, extendibility and integration at modeling and simulation levels. Any simulation workflow can be defined by appropriately combining the relevant modules. Different types of analysis can be specified such as sensitivity, design of experiment and optimization. Any combination of engine parameters can be selected as design variables, and multi-disciplinary requirements and constraints at different operating points in the flight envelope can be specified. The framework implementation is exemplified through the optimization of an ultra-high bypass ratio geared turbofan engine with a variable area fan nozzle, for which specific aircraft requirements and technology limits apply. Although the optimum design resulted in double-digit fuel-burn benefits compared to current technology engines, it did not meet engine-response requirements, highlighting the need to include transient-performance assessments as early as possible in the preliminary engine design phase.

A mean-line compressor performance calculation method is presented that covers the entire operating range, including the choked region of the map. It can be directly integrated into overall engine performance models, as it is developed in the same simulation environment. The code materializing the model can inherit the same interfaces, fluid models, and solvers, as the engine cycle model, allowing consistent, transparent, and robust simulations. In order to deal with convergence problems when the compressor operates close to or within the choked operation region, an approach to model choking conditions at blade row and overall compressor level is proposed. The choked portion of the compressor characteristics map is thus numerically established, allowing full knowledge and handling of inter-stage flow conditions. Such choking modelling capabilities are illustrated, for the first time in the open literature, for the case of multi-stage compressors. Integration capabilities of the 1D code within an overall engine model are demonstrated through steady state and transient simulations of a contemporary turbofan layout. Advantages offered by this approach are discussed, while comparison of using alternative approaches for representing compressor performance in overall engine models is discussed.