Πλοήγηση ανά Συγγραφέα "Goulas, A."
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Τεκμήριο Computational modeling of vortex breakdown control on a delta wing(2013) Vlahostergios, Z.; Missirlis, D.; Yakinthos, K.; Goulas, A.We present an effort to model the development and the control of the vortex breakdown phenomenon on a delta wing. The pair of the vortices formed on the suction side of a delta wing is the major contributor to the lift generation. As the angle of attack increases, these vortices become more robust, having high vorticity values. The critical point of a delta wing operation is the moment when these vortices, after a certain angle of attack, are detached from the wing surface and wing stall occurs. In order to delay or control the vortex breakdown mechanism, various techniques have been developed. In the present work, the technique based on the use of jet-flaps is numerically investigated with computational fluid dynamics by adopting two eddy-viscosity turbulence models. The computational results are compared with the experimental data of Shih and Ding (1996). It is shown that between the two turbulence models, the more advanced one, which adopts a non-linear constitutive expression for the Reynolds-stresses, is capable to capture the vortex breakdown location for a variety of jet exit angles. The performance assessment of the models is followed by the investigation of the effect of the jet-flap on the lift and drag coefficients.Τεκμήριο Modeling pressure drop of inclined flow through a heat exchanger for aero-engine applications(2007-06) Missirlis, D.; Yakinthos, K.; Storm, P.; Goulas, A.In the present work further numerical predictions for the flow field through a specific type of a heat exchanger, which is planned to be used in the exhaust nozzle of aircraft engines. In order to model the flow field through the heat exchanger, a porous medium model is used based on a simple quadratic relation, which connects the pressure drop with the inlet air velocity in the external part of the heat exchanger. The aim of this work is to check the applicability of the quadratic law in a variety of velocity inlet conditions configured by different angles of attack. The check is performed with CFD and the results are compared with new available experimental data for these inlet conditions. A detailed qualitative analysis shows that although the quadratic law has been derived for a zero angle of attack, it performs very well for alternative non-zero angles. These observations are very helpful since this simple pressure drop law can be used for advanced computations where the whole system of the exhaust nozzle together with the heat exchangers can be modeled within a holistic approach.Τεκμήριο Modelling Operation of System of Recuperative Heat Exchangers for Aero Engine with Combined Use of Porosity Model and Thermo-Mechanical Model(2012) Yakinthos, K.; Missirlis, D.; Sideridis, A.; Vlahostergios, Z.; Seite, O.; Goulas, A.The present work describes an effort to model the operation of a system of recuperative heat exchangers of an aero engine for real engine operating conditions. The modelling was performed with the combined use of a porous medium model and a thermo mechanical model. The porous medium model was taking into account the heat transfer and pressure loss behaviour of the heat exchangers while the thermo mechanical one was used for the calculation of the wall temperature distribution of the elliptic tubes of the heat exchangers. As it is presented, the combined use of these models can provide a useful tool which can help in the prediction of the macroscopic behaviour of the system of recuperative heat exchangers of the aero engine which can be used for optimization purposes and numerical studies.Τεκμήριο Thermodynamics Cycle Analysis, Pressure Loss, and Heat Transfer Assessment of a Recuperative System for Aero-Engines(2015-04-01) Goulas, A.; Donnerhack, S.; Flouros, M.; Misirlis, D.; Vlahostergios, Z.; Yakinthos, K.Aiming in the direction of designing more efficient aero-engines, various concepts have been developed in recent years, among which is the concept of an intercooled and recuperative aero-engine. Particularly, in the area of recuperation, MTU Aero Engines has been driving research activities in the last decade. This concept is based on the use of a system of heat exchangers (HEXs) mounted inside the hot-gas exhaust nozzle (recuperator). Through the operation of the system of HEXs, the heat from the exhaust gas downstream the LP turbine of the jet engine is driven back to the combustion chamber. Thus, the preheated air enters the engine combustion chamber with increased enthalpy, providing improved combustion and by consequence, increased fuel economy and low-level emissions. If additionally an intercooler is placed between the compressor stages of the aero-engine, the compressed air is then cooled by the intercooler; thus, less compression work is required to reach the compressor target pressure. In this paper, an overall assessment of the system is presented with particular focus on the recuperative system and the HEXs mounted into the aero-engine's exhaust nozzle. The herein presented results were based on the combined use of CFD computations, experimental measurements, and thermodynamic cycle analysis. They focus on the effects of total pressure losses and HEX efficiency on the aero-engine performance especially the engine's overall efficiency and the specific fuel consumption (SFC). More specifically, two different hot-gas exhaust nozzle configurations incorporating modifications in the system of HEXs are examined. The results show that significant improvements can be achieved in overall efficiency and SFC, hence contributing to the reduction of CO2 and NOx emissions. The design of a more sophisticated recuperation system can lead to further improvements in the aero-engine efficiency in the reduction of fuel consumption. This work is part of the European funded research program Low Emissions Core engine Technologies (LEMCOTEC).