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.

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.

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.

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.

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.