Optimal Mission Analysis Accounting For Engine Aging And Emissions

Authors:Manousos Kelaidis, Nikolaos Aretakis, Tasos Tsalavoutas, Kostas Mathioudakis

Abstract

This paper describes an aircraft mission analysis procedure, comprising a flight simulation module, an engine model and an optimization method. The incorporation of engine deterioration modeling extends this procedure’s ability to estimate the on board performance of a given engine as it ages through time and use. Additionally, in order to investigate the environmental impact, pollutant emissions semi-empirical correlations have been introduced, after being adapted to available emissions data. The proposed procedure allows the optimization of a flight scenario for a variety of aircrafts, missions, and engine condition combinations, using an optimization method. The values of mission profile characteristics (e.g. cruise, altitude, and speed) that provide the optimum overall performance, regarding fuel conservation, time related costs, or pollutants production, are studied.

Performance Model 'Zooming' For In-Depth Component Fault Diagnosis

Authors:Aretakis N., Roumeliotis I., Mathioudakis K.

Abstract

A method giving the possibility for a more detailed gas path component fault diagnosis, by exploiting the "zooming" feature of current performance modelling techniques, is presented. A diagnostic engine performance model is the main tool that points to the faulty engine component. A diagnostic component model is then used to identify the fault. The method is demonstrated on the case of compressor faults. A 1-D model based on the "stage stacking" approach is used to "zoom" into the compressors, supporting a 0-D engine model. A first level diagnosis determines the deviation of overall compressor performance parameters, while "zooming" calculations allow a localization of the faulty stages of a multistage compressor. The possibility to derive more detailed information with no additional measurement data is established, by incorporation of empirical knowledge on the type of faults that are usually encountered in practice. Although the approach is based on known individual diagnostic methods, it is demonstrated that the integrated formulation provides not only higher effectiveness but also additional fault identification capabilities.

Short And Long Range Mission Analysis For A Geared Turbofan With Active Core Technologies

Authors:Alexiou A., Aretakis N., Roumeliotis I., Mathioudakis K.

Abstract

A novel engine concept, for reducing the environmental impact of gas turbines, is the Geared Turbofan with Active Core technologies (GTAC), investigated in the context of the European program NEWAC (New Aero Engine Core Concepts). Two performance models of this engine are created for short and long range aircraft applications and matched to manufacturer specifications. The engine performance data are used in a mission analysis module simulating typical aircraft applications. Compared to missions using Year 2000 in service engines, the results show a significant reduction in fuel consumption and noise levels. A significant reduction in NOx emissions requires the application of new technology combustor designs as developed e.g. in NEWAC.

Enhanced Training on Marine Gas Turbine Degradation Effects

Authors:Roumeliotis I., Aretakis N., Yfantis E., Mathioudakis K., Kapasakis P.

Abstract

This paper focuses on the degradation effects on marine gas turbine engines and is introducing the aspect of enhanced training in the field of performance monitoring and diagnostics via fault simulation. A particular performance model, TEACHES, built for on board training purposes in the frame of Virtual Lab, is employed to demonstrate the effects of typical faults on the operation and performance of a specific marine engine of interest. The model allows the presentation of basic rules of gas turbine engine behavior and enables users to indulge in different aspects of its operation using a graphics user interface. The faults can be easily introduced into different engine components and their impact on engine performance can be studied and evaluated allowing the derivation of faults signatures on monitoring parameters. A literature review was materialized in order to simulate the degradation effects on each component accurately.

Evaluation of Water Injection Effect on Compressor and Engine Performance and Operability

Authors:Roumeliotis I., Mathioudakis K.

Abstract

Gas turbine performance enhancement technologies such as inlet fogging, combustor water/steam injection and overspray are being employed by users in recent years without fully evaluating their effect on gas turbine performance and operability. The water injection techniques can significantly affect the engine operating point thus a careful analysis should precede the application of performance enhancement devices, especially when the devices are retrofitted to old engines or engines operating at extreme conditions. The present paper examines the most widespread techniques that implement water injection by using in-house models that can reproduce the effects of water injection on the gas turbine and compressor off-design operation. The results are analyzed with respect to both performance augmentation and engine operability in order to give further insight on gas turbine operation with water injection. The behaviour of the gas turbine is interpreted while the risks on engine integrity due to water injection are identified.

Direct-Transfer Pre-Swirl System: Performance Modelling, Validation And Optimisation

Authors:Alexiou A., Mathioudakis K.

Abstract

This paper describes the modelling of direct transfer pre-swirl cooling air delivery systems using a library of secondary air system components developed in an object-oriented simulation environment. The modelling accounts for the flow through the stationary pre-swirl nozzles and rotating receiver holes, the moments and convective heat transfer from the chamber surfaces and the mixing of seal flows. The model is validated against measured data from experimental rigs representative of aero-engine conditions. The modelling approach allows for rapid evaluation of alternative component designs for optimum overall performance at system or engine level.

Optimal Mission Analysis Accounting For Engine Aging And Emissions

Authors:Kelaidis M., Aretakis N., Tsalavoutas A., Mathioudakis K

Abstract

This paper describes an aircraft mission analysis procedure, comprising a flight simulation module, an engine model and an optimization method. The incorporation of engine deterioration modeling extends this procedure's ability to estimate the on board performance of a given engine as it ages through time and use. Additionally, in order to investigate the environmental impact, pollutant emissions semi-empirical correlations have been introduced, after being adapted to available emissions data. The proposed procedure allows the optimization of a flight scenario for a variety of aircrafts, missions, and engine condition combinations, using an optimization method. The values of mission profile characteristics (e.g. cruise, altitude, and speed) that provide the optimum overall performance, regarding fuel conservation, time related costs, or pollutants production, are studied.

Secondary Air System Component Modelling For Engine Performance Simulations

Authors:Alexiou A., Mathioudakis K.

Abstract

This paper describes the modelling of typical secondary air system elements such as rotating orifices, seals and flow passages with heat and work transfer from the surrounding surfaces. The modelling is carried out in an object-oriented simulation environment that allows the creation of different configurations in a simple and flexible manner. This makes possible to compare the performance between different designs of individual components or complete secondary air systems as well as integrate them directly in whole engine performance models. The modelling is validated against published experimental data and computational results. An example of implementation in an engine model is also presented.

Advanced Capabilities for Gas Turbine Engine Performance Simulations

Authors:Alexiou A., Baalbergen E., Mathioudakis K., Kogenhop O., Arendsen P.

Abstract

This paper describes the integration of advanced methods such as component zooming and distributed computing, in an object-oriented simulation environment dedicated to gas turbine engine performance modelling. A 1-D compressor stage stacking method is used to demonstrate three approaches for integrating numerical zooming in an engine model. In the first approach a 1-D compressor model produces a compressor map that is then used in the engine model in place of the default one. In the second approach the results of the 1-D analysis are passed to the 0-D component through appropriate 'zooming' scalars. In the final approach the 1-D compressor component directly replaces the 0-D one in the engine model. Distributed computing is realized using Web Services technology. The implementation steps for a distributed scenario are presented. The standalone compressor stage stacking method, in the form of a shared library, is placed in a remote site and can be accessed over the internet through a Web Service Operation (server side). An engine simulation is set up containing a 1-D compressor component which acts as the client for the Web Service operation. Future development of the tool?s advanced capabilities is finally discussed.

Correlations Adaptation for Optimal Emissions Prediction

Authors:Tsalavoutas A., Kelaidis M., Thoma N., Mathioudakis K.

Abstract

An approach for estimating the pollutants emitted from a gas turbine using semi-empirical correlations is described. An extensive literature review has been carried out, in order to obtain information already available in the public domain, on the subject of pollutants emitted from turbine engines and on the effect of different parameters on them. It is shown that application of correlations in their original form does not provide a reliable estimation of emissions. Such estimation requires adaptation to the particular case studies. The possibility of adapting the considered semi-empirical correlations to available emissions measurements, through the use of optimization method is further studied. Multivariate analysis, for the establishment of generic correlations had been also applied. Results are presented and compared to the test data that derive from the dry performance of an industrial turbine and a turbojet military engine. It is demonstrated that a good predictive ability can be established.

A Virtual Laboratory for Education On Gas Turbine Principles And Operation

Authors:Mathioudakis K, Aretakis N., Kotsiopoulos P., Yfantis E.

Abstract

A software package created for educating engineering students on the principles of gas turbines is presented. It starts from the presentation of basic material on the principles of gas turbine components operation (turbomachinery, combustion chambers, inlets, exhausts). The usual textbook material is supported by audiovisual material that enhances the student's ability to assimilate the principles taught. Computational tools are included, allowing the execution of design studies as well as performance simulations, for a wide range of gas turbine types. Both aircraft and land based gas turbines are covered. A user friendly interface allows the execution of calculations, whose results can be presented in a variety of formats, with the help of a flexible graphical user interface. A number of specific engines have been chosen to be represented, one of the reasons for this choice being that the package in its current form is primarily intended for use by air force and naval academy students, expected to come in contact with the specific engines employed by the corresponding organizations. Finally, a number of laboratory exercises are included. The exercises are performed in a way that is a reproduction of actual laboratory tests. The software employs audio-visual effects, including videos and other animations, to support the instruction of gas turbine principles, and is implemented in a classroom specifically designed for this purpose. The audiovisual effects are employed to transfer the actual physical reality into the classroom, creating thus the virtual environment.

Gas Turbine Engine Performance Model Applications Using An Object-Oriented Simulation Tool

Authors:Alexiou A., Mathioudakis K.

Abstract

Engine performance models are used throughout the life cycle of an engine from conceptual design to testing, certification and maintenance. The objective of this paper is to demonstrate the use and advantages of an engine performance model, developed using an object-oriented simulation tool, for the following applications: - Building an engine model from existing engine components and running steady state and transient calculations - Development and integration of a new cooled turbine component in the existing engine model - Accessing the engine model from an external application - Using an external legacy routine in the engine model.

Analysis of moisture condensation during air expansion in turbines

Authors:Roumeliotis I., Mathioudakis K.

Abstract

Water is always present in the atmospheric air in the form of vapour. As air of low temperature expands through the turbine condensation may occur. Condensation gives rise to several problems in materialization of the air cycle as it results in temperature rise thus to different conditions than the expected at the turbine exit. Also in most air cycle applications, liquid water must be removed from the air stream before it gets to the cooled space. In the case that turbine exit temperature is very low; there is the possibility of ice particles formation. A method allowing the evaluation of air properties when condensation occurs is required in order to examine its effect on the cycle and optimize the operating envelope. The present paper describes a thermodynamic equilibrium method for predicting the occurrence of condensation and calculating the mixture properties once condensation has occurred. The method has been validated against the experimental results from a turbocharger turbine. The experimental results show that condensation can cause significant alteration to the turbine exit conditions. It is demonstrated that condensation can be predicted and the mixture properties after condensation can also be accurately evaluated.

Water Injection Effects on Compressor Stage Operation

Authors:Roumeliotis I., Mathioudakis K.

Abstract

In the present paper, experimental work concerning the effect of water injection on a compressor stage is presented. The effect on compressor stage performance and stability is examined for water injection up to 2%. The behaviour of the air flow in the blade rows is examined through aerodynamic measurements. The results indicate that although the water injection appears to not have any significant effect on the flow pattern and to stage pressure rise and stall margin, there is a measurable effect on compression efficiency which seems to result mainly from losses of mechanical nature and water acceleration. The efficiency degradation is proportional to the water ratio entering the engine.

The Influence Of Heat Transfer Effects On Turbine Performance Characteristics

Authors:Stamatis A., Mathioudakis K.

Abstract

A method allowing the evaluation of the effects related to heat transfer to the turbine blades on its performance characteristics is presented. The effects investigated are related to the change of passage dimensions, resulting from heat transfer and the change in flow field, exhibited mainly as a change in the boundary layer development due to the same reason. -Change of hot gas temperature combined with cooling air temperature and possibly flow rate, result in a change of the temperature of the blade material, leading to dimension changes, because of the thermal expansion (dilatation) . The changes in dimensions are directly linked to turbine performance. An immediate consequence is a modification of the mass flow characteristic, because of a change of the throat area. -Heat transfer also influences the properties of the gas flowing through the passage and in particular the characteristics of the boundary layers developing on the nozzle vanes and hub, tip endwals. Change of the thickness of this layer results in a change of blockage through the passage, a fact that influences directly the turbine flow function. The influence of both effects on turbine performance is studied. The study is performance oriented, aiming to the derivation of simplified models, which can be introduced in engine cycle decks.

Evaluation of Interstage Water Injection Effect on Compressor And Engine Performance

Authors:Roumeliotis I., Mathioudakis K.

Abstract

The present paper examines the effect of water injection at the compressor inlet or between stages, on its operation. A wet compression model coupled with an engine performance model is used. The wet compression model produces the compressor performance map when water is present and consists of a one dimensional stage stacking model, coupled with a droplet evaporation model. The effect of water injection on overall performance and individual stage operation is examined. The map generation procedure is embedded in an engine performance model and a study of water injection effect on overall engine performance is undertaken. The possibility to evaluate the effect on various parameters such as power, thermal efficiency, surge margin, as well as the progression of droplets through the stages is demonstrated. The results indicate that water injection causes significant stage rematching, leading the compressor towards stall and that the performance enhancement is greater as the injection point moves towards compressor inlet.

Development of Gas Turbine Performance Models Using a Generic Simulation Tool

Authors:Alexiou A., Mathioudakis K.

Abstract

An approach for gas turbine engine modelling using a general purpose object-oriented simulation tool is described. A commercially available such tool that can be adapted to different fields, through the creation of reusable modelling component libraries representing parts or equipment of a physical system is employed. Libraries are developed using an object-oriented language. The possibility for quick implementation of new models and rapid analysis of results, through the use of a graphical user interface is demonstrated. A turbofan model, developed for both steady state and transient performance simulation, is used to illustrate the advantages offered by this approach. Results are presented and compared to those produced by an industry-accepted model. The flexibility of incorporating particular features into a model is demonstrated by presenting the implementation of adaptive features and a study of engine frequency response.

Gas Turbine Test Parameters Corrections Including Operation With Water Injection

Authors:Mathioudakis K.

Abstract

Methods for correcting data from gas turbine acceptance testing are discussed, focusing on matters which are not sufficiently covered by existing standards. First a brief outline is presented of the reasoning on which correction curves are based. Typical performance correction curves are shown together with the method of calculating mass flow rate and turbine inlet temperature from test data. A procedure for verifying guarantee data at a specific operating point is then given. Operation with water injection is then considered. Ways of correcting performance data are proposed, and the reasoning of following such a procedure is discussed. Corrections for water amount as well as power and efficiency are discussed. Data from actual gas turbine testing are used to demonstrate how the proposed procedure can be applied in actual cases of acceptance testing.

Performance Analysis Of Twin-Spool Water Injected Gas Turbines Using Adaptive Modelling

Authors:Roumeliotis I., Aretakis N., Mathioudakis K.

Abstract

The development of an adaptive performance model for multi-spool gas turbines, equipped with the possibility of water injection is described. The model covers water injection at engine inlet, between the compressors and at the compressor exit. The selection of modification factors and the procedure for adapting component characteristics to overall performance data is discussed. A case of adaptation to overall performances is presented. The use of the model for studying overall engine and components performance is demonstrated. It is shown how operation with water injection modifies component operation, a fact that allows the identification of a wider range of the performance characteristics, in comparison to dry operation. This fact may also increase the diagnostic ability of techniques employing adaptive models. The sensitivity of diagnostic procedures to the different modes of operation of a gas turbine of the type described in the paper is also discussed.

Design and Development of a Small Jet Engine Test Cell

Authors:Mathioudakis K., Argyropoulos P.

Abstract

The process of designing a test cell for a small jet engine is described. The test cell was designed to support educational activities in the field of gas turbines. The design was undertaken by a student, as a part of his requirements for obtaining a Mechanical Engineering Degree. The requirements for the design are first laid out, according to the characteristics of the engine to be tested and the restrictions posed by the installation location. The phases of designing and construction are presented. Technical aspects of design choices for setting up the test chamber are presented. The choice of instrumentation and the way it is arranged is discussed. Results from the first tests conducted on the finished facility are presented, first, to check how design targets have been met and second, to show what kind of information can be provided to support gas turbine courses. The fact that a multidisciplinary knowledge is applied in the project is Educational benefits for the student that has undertaken the project are discussed, while particular choices made for a better suitability for subsequent educational use are highlighted.

Turbomachinery Flow Measurements Using Long-Nose Probes

Authors:Doukelis A., Mathioudakis K.

Abstract

The present work provides a detailed account of a pneumatic measuring technique appropriate for flow field measurements in turbomachinery configurations, making use of long-nose 5-hole probes. The way of obtaining flow quantities in a frame of reference on the sensing head of the probe is first addressed. Transformation of velocity co-ordinates from the probe frame to a stationary frame, customary for turbomachinery flows, is then discussed. Sources of error are also discussed, with particular attention on those that can be introduced by the nose geometry and the co-ordinate transformations. The potential of the measuring technique is demonstrated by presenting the application of the technique for measurements in an annular cascade facility. The results are compared to results obtained by a 3-D Laser-Doppler Anemometer.

Evaluation of Steam and Water Injection Effects on Gas Turbine Operation Using Explicit Analytical Relations

Authors:Mathioudakis K.

Abstract

The changes in performance of a gas turbine resulting from the injection of steam or water in the combustion chamber are evaluated using explicit analytic relations. From the values of performance parameters at an operating point without injection, the changes in fuel amount, power output and efficiency are evaluated. The difference in behaviour of the case of water and steam injection are highlighted and explained. It is shown that the movement of operating point on the compressor map, for single and twin shaft turbines, can also be predicted. Comparison to predictions of computer models show that the deviations are predicted accurately. Design data from a large number of commercial gas turbines are used to show the range of variation of parameter deviations and provide some general guidelines as to the size of expected parameter deviations for any gas turbine, when water or steam are injected between the compressor exit and the turbine inlet.

Analysis of the Effects of Water Injection on the Performance of a Gas Turbine

Authors:Mathioudakis K.

Abstract

The effect of water injection in the combustion chamber of an industrial gas turbine is studied by means of analytic relations. Equations for the estimation of changes in the main performance parameters are provided. The relations are derived on the basis of an order of magnitude analysis and taking into account variation of gas properties due to water injection as well as changes in the interrelation of component performance parameters. It is shown that water/fuel ratio is the main parameter on which performance deviations depend. Data from the performance testing of an industrial gas turbine are used to check the validity of the proposed relations. The comparison of the predictions to the test data shows that the mechanisms of performance deviations are well modeled by the analysis presented.

On Board Adaptive Models: A General Framework and Implementation Aspects

Authors:Stamatis A., Kamboukos Ph., Aretakis N., Mathioudakis K.

Abstract

The principles on which an adaptive engine performance model is based are first discussed. The mathematical ways of matching given performance data are presented and their implications for practical implementation are discussed. The consequences of using a number of measurements equal or fewer than the number of adapting parameters are analysed. The numerical behaviour of an adaptive model is also discussed. Solution methods based on non-linear system solvers are compared to methods using optimisation techniques. Execution time requirements are also discussed for the different approaches and implications for possible on-line or off-line applications are evaluated.

Real Time Engine Model Implementation For Adaptive Control & Performance Monitoring of Large Civil Turbofans

Authors:Stamatis A., Mathioudakis K., Ruiz J., Curnock B.

Abstract

A real time engine model to be used as an onboard observer in Large Civil Turbofans has been developed. The main features of this Real Time Model are its non-linear physical structure (identical with a detailed transient model, which may represent the real engine) as well as its ability to adapt itself to the engine condition. General and specific requirements for the targeted model have been set, evolution of the model is presented and various investigations concerning the ability of the model to satisfy these requirements are discussed. The conclusion is that the model is faster than real time in terms of a realistic time step for current turbofan engines controllers using a processor with computing power about ten times less than the current existing processors. It is also worth mentioned that this speed is achieved without sacrificing model accuracy. In general maximum errors less than 1% can be obtained using no more than five fixed iterations in the model in order to achieve this speed.

Effects Of Anti-Icing System Operation On Gas Turbine Performance And Monitoring

Authors:Mathioudakis K., Tsalavoutas A.

Abstract

The effect of operation of compressor bleed anti-icing on the performance of an industrial gas turbine is analysed. The effect of putting this system in operation is first qualitatively discussed, while the changes on various performance parameters are derived by using a computer engine performance model. The main point of the paper is the study of the effect of anti-icing system operation on parameters used for engine condition monitoring. It is shown that operation of the anti-icing system causes an apparent modification of such parameters, which may reduce the diagnostic ability of an on-line monitoring system and produce false alarms. It is shown that by incorporating the effect of anti-icing system operation into a diagnostic engine model, such problems can be avoided and the diagnostic ability of the system is not influenced by anti-icing activation. The analysis presented is substantiated through experimental data from a twin shaft gas turbine operating in the field.

Performance Analysis of Industrial Gas Turbines for Engine Condition Monitoring

Authors:Mathioudakis K., Stamatis A., Tsalavoutas A., Aretakis N.

Abstract

This paper presents methods of analysing aerothermodynamic performance measurement data for the purpose of assessing the condition of the components of a gas turbine. Features of the methods are analysed in function of the available measurements and ways of extracting as much information as possible from a given measurement set are discussed. The principles discussed are highlighted by presenting results from application to data from operating industrial gas turbines. Particular applications discussed are the identié cation of deposits on the blades of a gas turbine used for power generation and the monitoring of compressor fouling on another industrial gas turbine.

Jet Engine Component Maps for Performance Modelling and Diagnostics

Authors:Sieros G., Stamatis A., Mathioudakis K.

Abstract

This paper describes an effort to model the performance maps of compressors and turbines (i.e., the relation between mass è ow, pressure ratio, and efé ciency), using analytical functions. Analytical functions are fitted to the available experimental data using a least-squares-type approach for determining the parameters of the é tting function. The success of using a particular function for an application is assessed through a suitably deé ned mean error of the model. Apart from presenting the method for setting up these analytical representations, applications to performance modeling and fault diagnosis are discussed. The change in model parameters is used to characterize changes of the engine condition and possibly diagnose occurring faults. The impact of introducing analytical component models into overall engine computer models, replacing a tabulated form of the component maps, is also discussed.

Adaptive Modelling of Jet Engine Performance With Application to Condition Monitoring

Authors:Lambiris B., Mathioudakis K., Stamatis A., Papailiou K.D.

Abstract

A method of simulation of the performance of jet engines, with the possibility of adapting to engine particularities, is presented. It employs an adaptation procedure coupled to a performance model solving the component matching problem. The proposed method can provide accurate simulation for engines of the same type, with differences that are due to manufacturing or assembly tolerances. It does not require accurate component maps, because they are derived during the adaptation procedure. It can also be used for health monitoring purposes, for component fault identification, and condition assessment. The effectiveness of the proposed method is demonstrated by application to two commercial jet engines.

Adaptive Simulation of Gas Turbine Performance

Authors:Stamatis A., Mathioudakis K., Papailiou K.D.

Abstract

A method is presented allowing the simulation of gas turbine performance with the possibility of adapting to engine particularities. Measurements along the gas path are used, in order to adapt a given performance model by appropriate modification of the component maps. The proposed method can provide accurate simulation for engines of the same type, differing due to manufacturing or assembly tolerances. It doesn't require accurate component maps, as they are derived during the adaptation process. It also can be used for health monitoring purposes, introducing thus a novel approach for component condition assessment. The effectiveness of the proposed method is demonstrated by application to an industrial gas turbine.

Modelling Contra-Rotating Turbomachinery Components For Engine Performance Simulations: The Geared Turbofan With Contra-Rotating Core Case

Authors:Alexiou A., Roumeliotis I., Aretakis N., Tsalavoutas A., Mathioudakis K.

Abstract

This paper presents a method of modelling contra-rotating turbomachinery components for engine performance simulations. The first step is to generate the performance characteristics of such components. In this study, suitably modified one-dimensional mean line codes are used. The characteristics are then converted to three-dimensional tables (maps). Compared to conventional turbomachinery component maps, the speed ratio between the two shafts is included as an additional map parameter and the torque ratio as an additional table. Dedicated component models are then developed that use these maps to simulate design and off-design operation at component and engine level.

Using this approach, a performance model of a geared turbofan with a Contra-Rotating Core (CRC) is created. This configuration was investigated in the context of the European program NEWAC (NEW Aero-engine core Concepts). The core consists of a seven-stage compressor and a two-stage turbine without inter-stage stators and with successive rotors running in opposite direction through the introduction of a rotating outer spool. Such a configuration results in reduced parts count, length, weight and cost of the entire HP system. Additionally, the core efficiency is improved due to reduced cooling air flow requirements.

The model is then coupled to an aircraft performance model and a typical mission is carried out. The results are compared against those of a similar configuration employing a conventional core and identical design point performance. For the given aircraft-mission combination and assuming a 10% engine weight saving when using the CRC arrangement over the conventional one, a total fuel burn reduction of 1.1% is predicted.

Assessing Alternative Fuels For Helicopter Operation

Authors:Alexiou A., Tsalavoutas A., Pons B., Aretakis N., Roumeliotis I., Mathioudakis K.

Abstract

At present, nearly 100% of aviation fuel is derived from petroleum using conventional and well known refining technology. However, the fluctuations of the fuel price and the vulnerability of crude oil sources have increased the interest of aviation industry in alternate energy sources. The motivation of this interest is actually twofold: firstly alternative fuels will help to stabilize price fluctuations by relieving the world wide demand for conventional fuel. Secondly alternative fuels could provide environmental benefits including a substantial reduction of emitted CO2 over the fuel life cycle. Thus, the ideal alternative fuel will fulfil both requirements: relieve the demand for fuels derived from crude oil and significantly reduce CO2 emissions.

In the present paper, the effects of various alternative fuels on the operation of a medium transport/utility helicopter are investigated using performance models of the helicopter and its associated turboshaft engine. These models are developed in an object-oriented simulation environment that allows a direct mechanical connection to be established between them in order to create an integrated model. Considering the case of a typical mission for the specific helicopter/engine combination, a comparative evaluation of conventional and alternative fuels is then carried out and performance results are presented at both engine and helicopter level.

Helicopter Engine Optimization For Minimum Mission Fuel Burn

Authors:Alexiou A., Pons B., Cobas P., Mathioudakis K., Aretakis N.

Abstract

The paper presents an approach for optimizing the design point inlet mass flow rate and overall pressure ratio of a turboshaft engine in order to minimize fuel burn over a specific mission of a medium transport-utility helicopter engine.

The method employs performance models of the helicopter and associated turboshaft engines and is suitable for the preliminary design of a new engine or the re-design of an existing one.

It uses empirical correlations to account for changes in turbomachinery component efficiencies and engine/helicopter weight due to the change of inlet corrected mass flow from a reference value. The turbine cooling flows are adjusted according to the specified upper limit of turbine rotor inlet temperature. The surge margin must be within a specified value while pressure ratio changes must allow the re-introduction of cooling/sealing air flows back into the main flow.

Regarding the mission, the cruise altitude and total distance travelled are fixed while the velocity of best range during cruise and the velocity of best endurance and maximum rate of climb are recalculated based on the new helicopter weight due to changes in engine size and required mission fuel. The total reduction in mission fuel burn depends on the limits set by the designer.

Turbofan Engine Health Assessment From Flight Data

Authors:Aretakis N., Roumeliotis I., Alexiou A., Romesis C., Mathioudakis K.

Abstract

The paper presents the use of different approaches to engine health assessment using on-wing data obtained over a year from an engine of a commercial short-range aircraft. The on-wing measurements are analyzed with three different approaches, two of which employ two models of different quality. Initially, the measurements are used as the sole source of information and are post-processed utilizing a simple “model” (a table of corrected parameter values at different engine power levels) to obtain diagnostic information. Next, suitable engine models are built utilizing a semi-automated method which allows for quick and efficient creation of engine models adapted to specific data. Two engine models are created, one based on publicly available data and one adapted to engine specific on-wing “healthy” data. These models of different detail are used in a specific diagnostic process employing model-based diagnostic methods, namely the Probabilistic Neural Network (PNN) method and the Deterioration Tracking method. The results demonstrate the level of diagnostic information that can be obtained for this set of data from each approach (raw data, generic engine model or adapted to measurements engine model). A sub-system fault is correctly identified utilizing the diagnostic process combined with the engine specific model while the Deterioration Tracking method provides additional information about engine deterioration.

Development and Integration of Rain Ingestion Effects in Engine Performance Simulations

Authors:Roumeliotis I., Alexiou A., Aretakis N., Sieros G., Mathioudakis K.

Abstract

Rain ingestion can significantly affect the performance and operability of gas turbine aero-engines. In order to study and understand rain ingestion phenomena at engine level, a performance model is required that integrates component models capable of simulating the physics of rain ingestion. The current work provides, for the first time in the open literature, information about the set-up of a mixed-fidelity engine model suitable for rain ingestion simulation and corresponding overall engine performance results. Such a model can initially support an analysis of rain ingestion during the pre-design phase of engine development. Once components and engine models are validated and calibrated versus experimental data, they can then be used to support certification tests, the extrapolation of ground test results to altitude conditions, the evaluation of control or engine hardware improvements and eventually the investigation of inflight events.

In the present paper, component models of various levels of fidelity are firstly described. These models account for the scoop effect at engine inlet, the fan effect and the effects of water presence in the operation and performance of the compressors and the combustor. Phenomena such as velocity slip between the liquid and gaseous phases, droplet break-up, droplet-surface interaction, droplet and film evaporation as well as compressor stages re-matching due to evaporation are included in the calculations. Water ingestion influences the operation of the components and their matching, so in order to simulate rain ingestion at engine level a suitable multi-fidelity engine model has been developed in the PROOSIS simulation platform. The engine model’s architecture is discussed and a generic high bypass turbofan is selected as a demonstration test case engine.

The analysis of rain ingestion effects on engine performance and operability is performed for the worst case scenario, with respect to the water quantity entering the engine. The results indicate that rain ingestion has a strong negative effect on high-pressure compressor surge margin, fuel consumption and combustor efficiency, while more than half of the water entering the core is expected to remain unevaporated and reach the combustor in the form of film.

Contra Rotating Propeller Modelling for Open Rotor Engine Performance Simulations

Authors:Alexios Alexiou, Charalambos Frantzis, Nikolaos Aretakis, Vassilios Riziotis, Ioannis Roumeliotis, Konstantinos Mathioudakis

Abstract

This paper presents a method for modelling contra-rotating propellers (CRP) for engine performance simulations. An inhouse free-wake lifting surface tool (GENUVP) is used to generate suitable performance maps for each propeller that express power and thrust coefficient in terms of advance ratio, flight Mach number, speed ratio and blade pitch angle of each propeller. Appropriate component models that utilize these maps are then developed in a commercial engine performance simulation environment (PROOSIS). Next, the propeller components are integrated in a direct-drive open rotor engine model. Finally, design point and off-design simulations are carried out that demonstrate the use of the model through studies of different propeller blade angle control strategies.

Industrial Gas Turbine Health and Performance Assessment With Field Data

Authors: I. Roumeliotis, N. Aretakis, A. Alexiou

Abstract

The paper presents a thorough analysis of historical data and results acquired over a period of two years through an online real-time monitoring system installed at a Combined Heat and Power (CHP) plant. For gas turbine health and performance assessment, a Gas Path Analysis tool based on the adaptive modeling method is integrated into the system. An engine adapted model built through a semi-automated method is part of a procedure which includes a steam/water cycle simulation module and an economic module used for power plant performance and economic assessment. The adaptive modeling diagnostic method allowed for accurate health assessment during base and part load operation identifying and quantifying compressor recoverable deterioration and the root cause of an engine performance shift. Next the performance and economic assessment procedure was applied for quantifying the economic benefit accrued by implementing daily on-line washing and for evaluating the financial gains if the off-line washings time intervals are optimized based on actual engine performance deterioration rates.

The results demonstrate that this approach allows continuous health and performance monitoring at full and part load operation enhancing decision making capabilities and adding to the information that can be acquired through traditional analysis methods based on heat balance and base load correction curves.

Direct Coupling of a Two-Dimensional Fan Model in a Turbofan Engine Performance Simulation

Authors: Ioannis Templalexis, Alexios Alexiou, Ioannis Roumeliotis, Vassilios Pachidis, Nikolaos Aretakis

Abstract

Coupling of high fidelity component calculations with overall engine performance simulations (zooming) can provide more accurate physics and geometry based estimates of component performance. Such a simulation strategy offers the ability to study complex phenomena and their effects on engine performance and enables component design changes to be studied at engine system level. Additionally, component interaction effects can be better captured. Overall, this approach can reduce the need for testing and the engine development time and cost.

Different coupling methods and tools have been proposed and developed over the years ranging from integrating the results of the high fidelity code through conventional performance component maps to fully-integrated three-dimensional CFD models.

The present paper deals with the direct integration of an inhouse two-dimensional (through flow) streamline curvature code (SOCRATES) in a commercial engine performance simulation environment (PROOSIS) with the aim to establish the necessary coupling methodology that will allow future advanced studies to be performed (e.g. engine condition diagnosis, design optimization, mission analysis, distorted flow).

A notional two-shaft turbofan model typical for light business jets and trainer aircraft is initially created using components with conventional map-defined performance. Next, a derivative model is produced where the fan component is replaced with one that integrates the high fidelity code. For both cases, an operating line is simulated at sea-level static take-off conditions and their performances are compared.

Finally, the versatility of the approach is further demonstrated through a parametric study of various fan design parameters for a better thermodynamic matching with the driving turbine at design point operation.

Assessment of Solar Steam Injection in Gas Turbines

Authors: C. Kalathakis, N. Aretakis, I. Roumeliotis, A. Alexiou, K. Mathioudakis

Abstract

The concept of solar steam production for injection in a gas turbine combustion chamber is studied for both nominal and part load engine operation. First, a 5MW single shaft engine is considered which is then retrofitted for solar steam injection using either a tower receiver or a parabolic troughs scheme. Next, solar thermal power is used to augment steam production of an already steam injected single shaft engine without any modification of the existing HRSG by placing the solar receiver/evaporator in parallel with the conventional one.

For the case examined in this paper, solar steam injection results to an increase of annual power production (~15%) and annual fuel efficiency (~6%) compared to the fuel-only engine. It is also shown that the tower receiver scheme has a more stable behavior throughout the year compared to the troughs scheme that has better performance at summer than at winter. In the case of doubling the steam-to-air ratio of an already steam injected gas turbine through the use of a solar evaporator, annual power production and fuel efficiency increase by 5% and 2% respectively.

Investigation of Different Solar Hybrid Gas Turbines and Exploitation of Rejected Sun Power

Authors: C. Kalathakis, N. Aretakis, I. Roumeliotis, A. Alexiou, K. Mathioudakis

Abstract

Solar hybrid gas turbine performance is studied through consideration of four engine configurations: a) single shaft, b) recuperated single-shaft, c) twin-shaft and d) two-spool threeshaft, intercooled, recuperated. For each configuration and for the same design point, the performance is obtained for two hybridization schemes: Fuel only engines Retrofitted for Solar operation (FRS) and engines designed with Solar only operation at the Design Point (SDP). In an attempt to further improve the benefits of hybridization, the concept of a Dual Fluid Receiver for exploiting the rejected solar power, during sunny hours with high irradiation, is demonstrated. Steam is produced by focusing the defocused mirrors of the heliostat field to a second receiver and injected into the combustion chamber.

For the cases examined, it can be concluded that FRS engines show better performance than SDP ones, since they exhibit higher thermal fuel efficiency and higher specific power. Concerning the configurations, an annual fuel saving of ~35% and an annual output reduction, ranging from 4% for the recuperated single-shaft configuration to 9% for the twin shaft configuration compared to the corresponding fuel-only engines is demonstrated. The inclusion of a Dual Fluid Receiver in an FRS engine removes the power penalty while it maintains the fuel saving benefit.

Concentrated Solar Power Components Toolbox in an Object Oriented Environment.

Authors: C. Kalathakis, N. Aretakis, I. Roumeliotis, A. Alexiou, K. Mathioudakis

Abstract

A toolbox for modeling solar components for gas and steam turbine Solar Thermal Power Plants (STPPs) is presented. It has been created in order to supplement the PROOSIS modeling environment that covers the power production parts. Solar and power production parts are both represented at a similar level of fidelity. The toolbox contains components for simulating all the individual solar elements used in STPPs in order to materialize Brayton, Rankine and Combined Cycles. Functionalities for computing solar irradiation properties as well as working fluid thermodynamic properties are included. The use of the toolbox is demonstrated through simulation cases at component and plant level, while its features, capabilities and merits are discussed. The developed capabilities offer the possibility to perform plant design optimization, operational support through performance prediction at various operating modes as well as assessment of the effect of components malfunctions.

Assessment of Solar Gas Turbine Hybridization Schemes.

Authors: C. Kalathakis, N. Aretakis, I. Roumeliotis, A. Alexiou, K. Mathioudakis

Abstract

A simulation environment allowing steady state and transient modeling is used for assessing several gas turbine based cycles proposed for solar hybridization. First, representative open cycle gas turbine configurations, namely, (a) single shaft (SS), (b) recuperated single-shaft, (c) twin shaft (TS), and (d) two-spool three-shaft, intercooled, recuperated, are evaluated. The importance of design point selection in terms of solar share value is highlighted. Solar steam injection gas turbine cycle (STIG) alternatives, namely, solar steam only and solar/fuel gas steam, are then assessed. Finally, the concept of a dual fluid receiver (DFR) for exploiting the rejected solar power by producing steam during sunny hours with high irradiation is demonstrated. The effects of hybridization on performance and operability are established and evaluated. Solarization effect on performance is estimated in terms of annual produced power and fossil fuel savings. The results indicate that the spool arrangement affects the suitability of a gas turbine for hybridization. Recuperated configurations performed better for the design constrains imposed by current technology solar parts. Solar steam injection is a promising solution for retrofitted fuel-only and conventional STIG engines.

Performance modelling of an ultra-high bypass ratio geared turbofan

Authors: Alexios Alexiou, Nikolaos Aretakis, Ioannis Roumeliotis, Ioannis Kolias, Kostas Mathioudakis

Abstract

In this paper, the main modelling aspects for setting up an Ultra-High Bypass Ratio (UHBR) Geared Turbofan (GTF) engine performance model with Variable Pitch Fan (VPF) and/or bypass Variable Area Nozzle (VAN) are first described. Next, a multi-point design (MPD) structure is presented considering performance requirements and thermal, structural and aerodynamic constraints at top-of-climb, take-off and cruise conditions. Using the MPD approach, multi-parametric studies are then carried out to generate a design space of engine cycles according to the specified targets and limits which are representative of a UHBR GTF in a narrow body aircraft for short range applications with an Entry Into Service (EIS) of 2025.

Direct Integration of Axial Turbomachinery Preliminary Aerodynamic Design Calculations in Engine Performance Component Models

Authors: I. Kolias, A. Alexiou, N.Aretakis, K. Mathioudakis

Abstract

In the context of an engine design calculation, isentropic or polytropic efficiencies of turbomachinery components are assumed at the outset of the cycle analysis and their values are updated or validated following the aerodynamic design of the components. In the present paper, aerodynamic design calculations of axial-flow compressors and turbines are directly integrated into the corresponding performance component models. This creates a consistent, single-step preliminary design and performance modelling process using a relatively small number of physical and geometric inputs.

The aerodynamic design for establishing a component’s overall efficiency is accomplished through a mean-line, stage by-stage approach where the stagewise isentropic efficiency is calculated employing either loss or semi-empirical correlations. From this process, the stagewise flow annulus radii are also obtained and are used to axially size the component stages assuming the blade aspect ratio and axial gapping distributions. The component flowpath geometry is then produced by simply “stacking” axially the component stages.

The developed method is validated against publicly available data for a high-pressure compressor and a low pressure turbine. Finally, the effectiveness of the method is demonstrated by considering the multi-point design of a High Bypass Ratio Geared Turbofan Engine with bypass Variable Area Nozzle.

Solar Hybrid Micro Gas Turbine Based on Turbocharger

Authors: C. Kalathakis, N.Aretakis, K. Mathioudakis

Abstract

The performance of solar hybrid Brayton cycle materialized by a micro-gas turbine based on a turbocharger is studied. The use of a turbocharger is aimed at investment cost reduction and construction simplification. Two configurations are investigated, namely hybrid and solar-only. Design aspects are discussed, in view of the requirement for minimizing the cost of electricity produced. A key parameter is the turbine inlet temperature and its effect on performance is investigated. The effect of heliostat field size is also investigated. Augmentation of the maximum temperature leads to better performance, as a result of higher cycle efficiency. Solar-only configuration features are compared with hybrid ones and the contribution of different cost components to the final electricity cost is discussed.

Simulation models for supporting the solar thermal power plant operator

Authors: C. Kalathakis, N.Aretakis, I. Roumeliotis, A. Alexiou, K. Mathioudakis

Abstract

The benefits that may accrue for the operators of Solar Thermal Power Plants by integrating simulators to everyday operation and maintenance management is demonstrated by using a simulation environment allowing steady state and transient modelling. Two representative STPPs are used as test cases, namely a hybrid solar gas turbine plant and a solar steam turbine plant. The plants operation is simulated for different operating modes utilizing annual meteorological data. Component faults that may occur during operation, such as mirror soiling and misalignment are studied. The effects of different operating modes on performance and operability are established and evaluated. The effect of components degradation on performance is assessed, the overall plant performance deterioration is quantified, and the possibility for selecting optimal maintenance planning is discussed.

A Marine Turbocharger Retrofitting Platform

Authors: K. Ntonas, N.Aretakis, I. Roumeliotis, K. Mathioudakis

Abstract

A turbocharger retrofitting platform utilizing 1D models for calculating turbomachinery components maps and a fully coupled process for integration with the turbomachinery components and the diesel engine, is presented. The platform has been developed with two modes of operation, allowing the retrofitting process to become fully automatic. In the first mode, available turbo-components are examined, in order to select the one that best matches the entire engine system, aiming to retain or improve the diesel engine efficiency. In the second mode, an optimization procedure is employed, in order to redesign the compressor to match the entire system in an optimum way. Dimensionless parameters are used as optimization variables, for a given compressor mass flow and power.

A retrofitting case study is presented, where three retrofitting options are analyzed (compressor retrofit, turbocharger retrofit and compressor redesign). In the first and second option, turbocharger retrofitting is carried out, using available turbo-components. It is shown that initial performance cannot be reconstituted using off-the-self solutions. In the third option, compressor designing is performed, using the optimization mode, in order to provide an improved retrofitting solution, aiming to at least reconstituting the original diesel engine performance. Finally, a CFD analysis is carried out, in order to validate the compressor optimization tool capability to capture the performance trends, based on geometry variation.

Turboelectric Distributed Propulsion Modelling Accounting For Fan Boundary Layer Ingestion And Inlet Distortion

Authors: G. Athanasakos, N.Aretakis, A. Alexiou, K. Mathioudakis

Abstract

A modelling approach of Boundary Layer Ingesting (BLI) propulsion systems is presented. Initially, a distorted compressor model is created utilizing the parallel compressor theory to estimate the impact of inlet distortion on fan performance. Next, a BLI propulsor model is developed considering both distortion effects and reduced inlet momentum drag caused from boundary layer ingestion. Finally, a Turbo-electric Distributed Propulsion (TeDP) model is set up, consisting of the BLI propulsor model, the associated turboshaft engine model and a representation of the relevant electrical system. Each model is validated through comparison with numerical and/or experimental data.

A design point calculation is carried out initially to establish propulsor key dimensions for a specified number of propulsors and assuming common inlet conditions. Parametric design point analyses are then carried out to study the influence of propulsors number and location under different inlet conditions, by varying fan design pressure ratio between 1.15 and 1.5. BLI and non BLI configurations are compared at propulsion system level to assess the BLI benefits. The results show that maximum BLI gains of 9.3% in TSFC and 4.7% in propulsive efficiency can be achieved with 16 propulsors and FPR=1.5, compared to podded propulsors, while further benefits can be achieved by moving the propulsor array backwards in the airframe.

Application of an Advanced Adaptation Methodology for Gas Turbine Performance Monitoring

Authors: P. Rompokos, N.Aretakis, I. Roumeliotis, K. Mathioudakis

Abstract

Adaptive modelling diagnostic methods are valuable tools for gas turbine performance and condition monitoring. Component maps capable of accurate representation of engine operation are not available to the engine operators. In this context, adaptive methods can be used for tuning the component maps for simulating accurately the engine performance throughout the whole operating envelope. In most cases, the map tuning is performed at a single operating point or operating line and although scaled maps can provide accurate results close to the reference points, deviations may significantly increase away from these reference points. For industrial gas turbines, in the past, this was not a major issue, given that most engines operated at or close to baseload. Currently, due to the increased share of renewable power in the generation mix in Europe, there is a shift of industrial gas turbines operating mode from baseload to load following and part load, thus there is a need for accurately simulating engine operation in a broader operating range. This paper presents a component map adaptation methodology integrating several methods applied in the literature in six steps. The novel methodology is applied to on-engine measurements from a heavy-duty gas turbine and the betterment on simulation achieved from each step is quantified. The adapted component maps enable accurate engine condition monitoring as demonstrated by a second test case for an industrial twin shaft engine where operating data spanning over four months are assessed.

Novel Aero-Engine Multi-Disciplinary Preliminary Design Optimization Framework Accounting for Dynamic System Operation and Aircraft Mission Performance

Authors: A. Alexiou, N. Aretakis, I. Kolias, K. Mathioudakis

Abstract

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.

Axial Compressor Mean-Line Analysis: Choking Modelling and Fully-Coupled Integration in Engine Performance Simulations.

Authors: I. Kolias, A. Alexiou, N. Aretakis, K. Mathioudakis

Abstract

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.

A Marine Turbocharger Compressor Multi-Point 3D Design Optimization Tool

Authors: K. Ntonas, N.Aretakis, K. Mathioudakis

Abstract

A marine turbocharger 3D compressor design tool, implemented on an existing marine turbocharger retrofit platform is presented. It produces 3D centrifugal compressor geometry for optimal compressor retrofit. It encompasses two modules, allowing the design process to become fully automatic. First, a 1D compressor multi-point design optimization process is carried out, aiming to provide a fast and reliable solution based on Turbocharged diesel Engine range of operation. Structural integrity is ensured by using simplified structural analysis. Dimensionless parameters are used as optimization variables, for a given nominal compressor mass flow and power. Then a CFD compressor multi-point design optimization process is carried out, producing optimized 3D compressor geometry. It complies with the Turbocharged diesel Engine range of operation, while structural integrity is ensured by using Finite Element analysis. A turbocharger compressor design case study is presented. First, a turbocharger 1D compressor design is carried out, aiming to at least reconstituting the original diesel engine performance. This first module provides a reliable compressor initial geometry for the 3D design module. A fully 3D compressor design is then performed, using a CFD-FEA optimization process, in order to provide an improved retrofitting solution. Comparison between the multi-point and the traditional one-point design method, shows that the multi-point method provides a wider SFC reduction in the range that the Diesel engine normally operates.

1D multi-point marine turbocharger design, for optimal performance recovery.

Authors: K. Ntonas, N.Aretakis, O. Koskoletos, K. Mathioudakis

Abstract

An integrated turbocharger 1D design tool, allowing retrofit of both compressor and turbine is presented. An optimization procedure is employed, to design both compressor and turbine to match the entire turbocharged system in an optimal way. The optimization process focuses on engine specific fuel consumption reduction in the engine range of operation, while ensuring appropriate matching between turbomachinery components and the diesel engine. Structural integrity of both turbo-components is ensured by using simplified structural and modal analysis. Dimensionless parameters are used as optimization variables, for both compressor and turbine, allowing the design process to become fully automatic. The platform produces four optimal 1D geometries, of different possible centrifugal compressor diffuser and turbine combinations. The combination that gives the best improvement to the diesel engine operation is identified. A case study is presented, where all four turbocharger configurations are designed and analyzed aiming to at least recover the original diesel engine performance. The platform then sorts all four optimized turbocharger geometries based on annual fuel cost reduction. The best configuration achieves the largest fuel consumption reduction (0.4% for the case presented), while stable operation and structural integrity are ensured. Additionally, a study of how the new machine learning volute loss models affect the designed geometry is performed. Finally, a techno-economical assessment is performed in order to identify the most profitable retrofit option, turbocharger redesign being one of four possible turbocharger options considered by the authors. Redesigning the entire turbocharger is shown to provide the largest long term profit.

A Tool for the Design of Turbomachinery Disks for an Aero-Engine Preliminary Design Framework

Authors: Kolias, I.; Aretakis, N.; Alexiou, A.; Mathioudakis, K.

Abstract

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.

Aero-Engine Preliminary Design Optimization and Operability Studies Supported by a Compressor Mean-Line Design Module.

Authors: Alexiou A, Kolias I, Aretakis N, Mathioudakis K.

Abstract

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.

A Simplified Chemical Reactor Network Approach for Aeroengine Combustion Chamber Modeling and Preliminary Design

Authors: Villette S, Adam D, Alexiou A, Aretakis N, Mathioudakis K.

Abstract

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.

Determining Steady-State Operation Criteria Using Transient Performance Modelling and Steady-State Diagnostics.

Authors: Mathioudakis K., Aretakis N., Alexiou A

Abstract

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.