A. Tsalavoutas

Performance analysis of industrial gas turbines for engine condition monitoring

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 identification of deposits on the blades of a gas turbine used for power generation and the monitoring of compressor fouling on another industrial gas turbine.

Combining Advanced Data Analysis Methods for the Constitution of an Integrated Gas Turbine Condition Monitoring and Diagnostic System

This paper presents principles for the constitution of gas turbine monitoring and diagnostic systems which:a. are integrated, namely manage all the tasks essential for achieving a diagnosis (measurement, analysis, interpretation, historical data management etc.)b. employ different kind of processing methods in order to cover an extensive range of engine conditions, including direct data evaluation and data consistency checks, thermodynamic analysis, vibration analysis.The requirements to be fulfilled by an industrial gas turbine monitoring system are briefly reviewed and ways to achieve them are discussed, indicating how they can be materialized by implementation of specific techniques. Techniques previously derived by the group of the authors are implemented, and the merits they offer when used in combination are discussed. Features of a system, materialized according to the principles discussed, into an operating industrial gas turbine is presented. On-line application of advanced analysis techniques, such as adaptive performance modeling is discussed, on the basis of observations of the collected data.Data collected from an engine operating in the field are presented to substantiate the matters discussed, and cases of successful fault identification are shown.Copyright

Identifying Faults in the Variable Geometry System of a Gas Turbine Compressor

The influence of faults in the variable geometry (variable stator vanes) system of multistage axial compressor on the performance of an industrial gas turbine is investigated. An experimental investigation has been conducted, by implanting such faults into an operating gas turbine. The faults examined are individual stator vane mistunings of different magnitudes and located at different stages. Fault identification is based on the aerothermodynamic measurement data and is achieved by employing two different techniques, namely adaptive performance modeling and monitoring the circumferential distribution of the turbine exit temperature. It is observed that the deviations of the health indices produced by an adaptive performance model form patterns that can be used to identify the faults. The patterns characterize both the kind and the magnitude of the fault. On the other hand, the turbine exit temperature profile is also influenced and its change can be used as additional information, to increase the confidence level of the diagnosis (contrary to customary practice, which expects temperatures profiles to reflect only burner or turbine malfunctions).

Correlations Adaptation for Optimal Emissions Prediction

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.Copyright

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

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.Copyright

Instructing the Principles of Gas Turbine Performance Monitoring and Diagnostics by Means of Interactive Computer Models

The paper discusses how the principles employed for monitoring the performance of gas turbines in industrial duty can be explained by using suitable Gas Turbine performance models. A particular performance model that can be used for educational purposes is presented. The model allows the presentation of basic rules of gas turbine engine behavior and helps understanding different aspects of its operation. It is equipped with a graphics interface, so it can present engine operating point data in a number of different ways: operating line, operating points of the components, variation of particular quantities with operating conditions etc. Its novel feature, compared to existing simulation programs, is that it can be used for studying cases of faulty engine operation. Faults can be implanted into different engine components and their impact on engine performance studied. The notion of fault signatures on measured quantities is clearly demonstrated. On the other hand, the model has a diagnostic capability, allowing the introduction of measurement data from faulty engines and providing a diagnosis, namely a picture of how the performance of engine components has deviated from nominal condition, and how this information gives the possibility for fault identification.Copyright

DERIVATION OF COMPRESSOR STAGE CHARACTERISTICS, FOR ACCURATE OVERALL PERFORMANCE MAP PREDICTION

In the present paper a method for deriving stage characteristics, which can provide accurate prediction of a multistage compressor map is presented. The method combines optimization techniques with the principles of stage stacking. The stage characteristics are produced by modifying some initial generic ones, until the desired accuracy in the prediction at selected points on the overall map is achieved. There are several reasons why prediction based on the initial stage characteristics can be inaccurate, the following three being the main ones. The first is due to inaccuracy in the representation of the stage characteristics themselves. The second is due to lack of exact knowledge of the geometric data of the various stages. Finally the third reason consists of the “weak” modelling representation of complex physical phenomena with one dimensional approaches. Therefore, even when the exact stage characteristics are known, this does not guarantee the accurate prediction of the compressor performance. On account of the above, it is preferable to acquire realistic “effective” stage characteristics which can be used for synthesizing overall compressor characteristics and assessing the effects of stage faults. In this paper, both of these aspects are successfully tackled as demonstrated by applying the method to different test cases.Copyright

Computer models for education on performance monitoring and diagnostics of gas turbines

The paper discusses how performance models can be incorporated in education on the subject of gas turbine performance monitoring and diagnostics. A particular performance model, built for educational purposes, is employed to demonstrate the different aspects of this process. The way of building a model is discussed, in order to ensure the connection between the physical principles used for diagnostics and the structure of the software. The first aspect discussed is model usage for understanding gas turbine behaviour under different operating conditions. Understanding this behaviour is essential, in order to have the possibility to distinguish between operation in ‘healthy’ and ‘faulty’ engine condition. A graphics interface is used to present information in different ways such as operating line, operating points on component maps, interrelation between performance variables and parameters. The way of studying faulty engine operation is then presented, featuring a novel comparison to existing simulation programs. Faults can be implanted into different engine components and their impact on engine performance studied. The notion of fault signatures on measured quantities is explained. The model has also a diagnostic capability, allowing the introduction of measurement data from faulty engines and providing a diagnosis, namely a picture of how the performance of engine components has deviated from a ‘healthy’ condition

Uncertainty Reduction in Gas Turbine Performance Diagnostics by Accounting for Humidity Effects

The paper presents an analysis of the effect of ambient humidity on the performance of industrial gas turbines and examines the impact of humidity on methods used for engine condition assessment and fault diagnostics. First, the way of incorporating the effect of humidity into a computer model of gas turbine performance is described. The model is then used to derive parameters indicative of the “health” of a gas turbine and thus diagnose the presence of deterioration or faults. The impact of humidity magnitude on the values of these health parameters is studied and the uncertainty introduced, if humidity is not taken into account, is assessed. It is shown that the magnitude of the effect of humidity depends on ambient conditions and is more severe for higher ambient temperatures. Data from an industrial gas turbine are presented to demonstrate these effects and to show that if humidity is appropriately taken into account, the uncertainty in the estimation of health parameters is reducedCopyright

Effects of Anti-Icing System Operation on Gas Turbine Performance and Monitoring

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.Copyright