Browsing by Author "Triantafyllou, Theodoros"

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    The effect of inlet flow distortion on installed gas turbine performance.
    (2018-03) Triantafyllou, Theodoros; Pilidis, Pericles; Nikolaidis, Theoklis
    Military aircraft are often subjected to severe flight manoeuvres with high Angles of Attack (AOA) and Angles of Sideslip (AOSS). These flight attitudes induce non-uniform in flow conditions to their installed gas turbine engines which may include distortion of inlet total pressure and total temperature at the Aerodynamic Interface Plane (AIP). When the downstream compression system of the engine experiences such distorted inflow conditions its operation is significantly affected in that its aerodynamic performance is reduced along with its stall margin. Also the blade stress levels of the compression system increase and vibration becomes an issue. A large, complex facility is required to accurately test how the actual engines response to such distorted conditions. In addition to the engine support facilities, a full-scale inlet is needed to house the engine and a large secondary air supply system is needed to generate flight speed and altitude conditions relative to the inlet. As it can be easily imagined, the cost of this type of full scale testing is remarkably high. The objective of the present study is to develop a numerical method for the estimation of the installed gas turbine engine performance variations due to airflow distortion. This method will also provide the means to assess the compatibility of an airframe-engine set at a specific operating envelope, given the geometry of the upstream intake and the performance simulation model of the under examination gas turbine engine. In the present work, the distorted conditions at the interface between the intake and the engine have been numerically calculated with Computational Fluid Dynamics (CFD), where 27 different aircraft flight attitudes have been tested. As a baseline set of airframe-engine, were chosen an airframe inspired by the General Dynamics/LMAERO F-16 aircraft, equipped with a Pratt and Whitney F100-PW-229-like gas turbine engine. Also, the specified flow field was resolved by a commercial CFD code. The steady state total pressure distortion induced to the AIP due to the aircraft's flight attitude was estimated in terms of distortion descriptors. These parameters were then correlated to the surge margin of the downstream compression system. Following this methodology, it was concluded whether each one of the tested flight attitudes induced enough distortion to the AIP so as to surge the engine's FAN. Also the engine's performance variations due to airflow distortion have been also estimated in terms of net thrust changes. The obtained results justify the anticipated behaviour of the engine with degraded performance, in terms of resulted net thrust, when the aircraft flies with Angle of Sideslip (AOSS). Having the FAN shaft rotational speed as the controlled parameter, the net thrust percentage change between the uninstalled condition of the engine with rather uniform inflow and that when the engine is installed and exposed to different flight attitudes varies between -1.76% to -22.56% depending on the flight Mach number and the aircraft's flight attitude. Finally, all the results were combined and performance maps have been created that correlate the aircraft's flight attitude with the engine's net thrust.
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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.