Browsing by Author "Diakostefanis, Michail"

Now showing 1 - 7 of 7
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    Assessment of degradation equivalent operating time for aircraft gas turbine engines
    (Cambridge University Press, 2020-01-09) Alozie, Ogechukwu; Li, Yi-Guang; Diakostefanis, Michail; Wu, Xin; Shong, Xingchao; Ren, Wencheng
    This paper presents a novel method for quantifying the effect of ambient, environmental and operating conditions on the progression of degradation in aircraft gas turbines based on the measured engine and environmental parameters. The proposed equivalent operating time (EOT) model considers the degradation modes of fouling, erosion, and blade-tip wear due to creep strain, and expresses the actual degradation rate over the engine clock time relative to a pre-defined reference condition. In this work, the effects of changing environmental and engine operating conditions on the EOT for the core engine booster compressor and the high-pressure turbine were assessed by performance simulation with an engine model. The application to a single and multiple flight scenarios showed that, compared to the actual engine clock time, the EOT provides a clear description of component degradation, prediction of remaining useful life, and sufficient margin for maintenance action to be planned and performed before functional failure.
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    Internet Operation of Aero Gas Turbines
    (Cranfield University, 2014-10) Diakostefanis, Michail; Nikolaidis, Theoklis; Stillwell, Mark Lee; Barnes, S; Pilidis, Pericles
    Internet applications have been extended to various aspects of everyday life and offer services of high reliability and security. In the Academia, Internet applications offer useful tools for the remote creation of simulation models and real-time conduction of control experiments. The aim of this study was the design of a reliable, safe and secure software system for real time operation of a remote aero gas turbine, with the use of standard Internet technology at very low cost. The gas turbine used in this application was an AMT Netherlands Olympus micro gas turbine. The project presented three prototypes: operation from an adjacent computer station, operation within the Local Area Netwok (LAN) of Cranfield University and finally, remotely through the Internet. The gas turbine is a safety critical component, thus the project was driven by risk assessment at all the stages of the software process, which adhered to the Spiral Model. Elements of safety critical systems design were applied, with risk assessment present in every round of the software process. For the implementation, various software tools were used, with the majority to be open source API’s. LabVIEW with compatible hardware from National Instruments was used to interface the gas turbine with an adjacent computer work station. The main interaction has been established between the computer and the ECU of the engine, with additional instrumentation installed, wherever required. The Internet user interface web page implements AJAX technology in order to facilitate asynchronous update of the individual fields that present the indications of the operating gas turbine. The parameters of the gas turbine were acquired with high accuracy, with most attention given to the most critical indications, exhaust gas temperature (EGT) and rotational speed (RPM). These are provided to a designed real-time monitoring application, which automatically triggers actions when necessary. The acceptance validation was accomplished with a formal validation method – Model Checking. The final web application was inspired by the RESTful architecture and allows the user to operate the remote gas turbine through a standard browser, without requiring any additional downloading or local data processing. The web application was designed with provisions for generic applications. It can be configured to function with multiple different gas turbines and also integrated with external performance simulation or diagnostics Internet platforms. Also, an analytical proposal is presented, to integrate this application with the TURBOMATCH WebEngine web application, for gas turbine performance simulation, developed by Cranfield University.
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    Nitrogen as an environmentally friendly suppression agent for aircraft cargo fire safety
    (SAGE, 2021-08-03) Diakostefanis, Michail; Sampath, Suresh; Dinesh, Akhil; Beuermann, Rainer; Malkogianni, Areti
    Fire suppression systems in cargo compartments are a certification requirement for commercial aircraft safety. Halon production was banned and usage ends in 2040 according to Montreal Protocol for environmental reasons. This necessitates an alternative environmentally friendly agent. Quantitative analysis of nitrogen as agent established suitability of the suppression system. The Minimum Performance Standards specifies the qualification procedure of an agent through four scenarios – bulk load; containerised load; surface burning; and aerosol can explosion. Empirical sources from Airbus, independent computational fluid dynamics studies and small-scale cup-burner tests indicate suitability of nitrogen specific to aircraft cargo fire suppression. The nitrogen delivery system and the experimental apparatus are presented. Extensive commissioning tests verified instrumentation reliability. All the four scenarios were conducted at Cranfield University, in a replica of a wide-body aircraft cargo compartment. In a reduced oxygen environment (11%) obtained with nitrogen discharge, the aerosol can explosion tests were performed without any evidence of explosion or pressure increase beyond the expected baseline value. The surface burning scenario was completed successfully and passed the Minimum Performance Standard criteria. The maximum average temperature was found to be 220°C (limit – 293°C). All the scenarios passed the Minimum Performance Standard criteria for indicating successful prevention of Class B fire re-ignition. Similarly, the containerised and bulk-load scenarios obtained results that passed the Minimum Performance Standard criteria for successfully maintaining continued fire suppression for a specified period of time. The maximum average temperature in containerised-load fire scenario was found to be 210°C (limit – 343°C) and in bulk-load scenario was 255°C (limit – 377°C). Additional qualification criteria and system design are presented in this article according to the Minimum Performance Standard format. This work can be extended to introduce standard testing for safety critical systems, such as engine bay and lithium-ion fires.
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    Numerical assessment for aircraft cargo compartment fire suppression system safety
    (Sage, 2021-04-27) Xiong, Yifang; Diakostefanis, Michail; Dinesh, Akhil; Sampath, Suresh; Nikolaidis, Theoklis
    Fire on board an aircraft cargo compartment can lead to catastrophic consequences. Therefore, fire safety is one of the most important considerations during aircraft design and certification. Conventionally, Halon-based agents were used for fire suppression in such cases. However, an international agreement under the Montreal Protocol of 1994 banned further production of Halon and several other halocarbons considered harmful to the environment. There is therefore a requirement for new suppression agents, along with suitable system design and certification. This article aims to describe the creation of a mechanism to validate a preliminary design for fire suppression systems using Computational Fluid Dynamics and provide further guidance for fire suppression experiments in aircraft cargo compartments. Investigations were performed for the surface burning fire, one of the fire testing scenarios specified in the Minimum Performance Standard, using the numerical code Fire Dynamics Simulator. This study investigated the use and performance of nitrogen, a potential replacement for Halon 1301, as an environmentally friendly agent for cargo fire suppression. Benchmark fires using the pyrolysis model and fire design model were built for the surface-burning fire scenario. Compared with experiment results, the two Computational Fluid Dynamics models captured the suppression process with high accuracy and displayed similar temperature and gas concentration profiles. Fire consequences in response to system uncertainties were studied using fire curves with various fire growth rates. The results suggested that using nitrogen as a fire suppression agent could achieve a lower post-suppression temperature compared to a Halon 1301-based system. It can therefore be considered as a potential candidate for aircraft cargo fire suppression. Such work will feed directly into system safety assessments during the early design stages, where analyses must precede testing. Future work proposed for the application of this model can be extended to other fire scenarios such as buildings, shipping, and surface transport vehicles.
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    Numerical simulation of the airflow over a military aircraft with active intake
    (Sage, 2016-06-02) Triantafyllou, Theodoros; Nikolaidis, Theoklis; Diakostefanis, Michail; Pilidis, Pericles
    The aim of the study presented herein is to numerically predict the behaviour of the airflow around a flying military aircraft with an active intake in which the airflow may enter and travel all the way up to the aerodynamic interface plane (the analytical interface between the inlet and engine). Computational fluid dynamics is used as the basic tool. The geometry created consists of a full-scale military aircraft exposed to different flight conditions. The flow results are mainly focused at the aerodynamic interface plane since the present study is a part of a greater research effort to estimate how the airflow distortion induced to the engine’s face due to the aircraft’s flight attitude, affects the embedded gas turbine’s performance. The obtained results were validated through a direct comparison against similar experimental ones, collected from a wind tunnel environment.
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    Remote operation and monitoring of a micro aero gas turbine
    (Cambridge University Press, 2017-06-21) Diakostefanis, Michail; Nikolaidis, Theoklis; Sampath, Babu; Triantafyllou, Theodoros
    Internet applications have been extended to various aspects of everyday life and offer services of high reliability and security at relatively low cost. This project presents the design of a reliable, safe and secure software system for real-time remote operation and monitoring of an aero gas turbine with utilisation of existing internet technology, whilst the gas turbine is installed in a remote test facility This project introduces a capability that allows remote and flexible operation of an aero gas turbine throughout the whole operational envelope, as required by the user at low cost, by exploiting the available Internet technology. Remote operation of the gas turbine can be combined with other remote Internet applications to provide very powerful gas-turbine performance-simulation experimental platforms and real-time performance monitoring tools, whilst keeping the implementation cost at low levels. The gas turbine used in this experiment is an AMT Netherlands Olympus micro gas turbine and a spiral model approach was applied for the software. The whole process was driven by risk mitigation. The outcome is a fully functional software application that enables remote operation of the micro gas turbine whilst constantly monitors the performance of the engine according to basic gas turbine control theory. The application is very flexible, as it runs with no local installation requirements and includes provisions for expansion and collaboration with other online performance simulation and diagnostic tools. This paper will be presented at the ISABE 2017 Conference, 5-8 September 2017, Manchester, UK.
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    Stability assessment of an airflow distorted military engine’s FAN
    (SAGE, 2017-06-27) Triantafyllou, Theodoros; Nikolaidis, Theoklis; Diakostefanis, Michail; Pilidis, Pericles
    Military aircraft are often subjected to severe flight maneuvers with high angles of attack and angles of sideslip. These flight attitudes induce non-uniformity in flow conditions to their gas turbine engines, which may include distortion of inlet total pressure and total temperature at the aerodynamic interface plane. Operation of the downstream engine’s compression system may suffer reduced aerodynamic performance and stall margin, and increased blade stress levels. The present study presents a methodology of evaluating the effect of inlet flow distortion on the engine’s fan stability. The flow distortion examined was induced to the aerodynamic interface plane by means of changing the aircraft’s flight attitude. The study is based on the steady-state flow results from 27 different flight scenarios that have been simulated in computational fluid dynamics. As a baseline model geometry, an airframe inspired by the General Dynamics/LMAERO F-16 aircraft was chosen, which has been exposed to subsonic incoming airflow with varying direction resembling thus different aircraft flight attitudes. The results are focused on the total pressure distribution on the engine’s (aerodynamic interface plane) face and how this is manifested at the operation of the fan. Based on the results, it was concluded that the distorted conditions cause a shift of the surge line on the fan map, with the amount of shift to be directly related to the severity of these distorted conditions. The most severe flight attitude in terms of total pressure distortion, among the tested ones, caused about 7% surge margin depletion comparing to the undistorted value.