Special Issue "Secondary Air Systems in Gas Turbine Engines"

A special issue of Aerospace (ISSN 2226-4310).

Deadline for manuscript submissions: 28 August 2018

Special Issue Editor

Guest Editor
Dr. Erinc Erdem

School of Engineering, University of Glasgow, Glasgow G12 8QQ, Scotland, UK; TUSAS Engine Industries (TEI), Esentepe Mah. Cevreyolu Bulvari no.356, Eskisehir, Turkey
Website | E-Mail
Interests: aerothermal analysis; turbomachinery; modelling and simulation; ground testing; measurement techniques; propulsion

Special Issue Information

Dear Colleagues,

Modern gas turbine engines are presently being pushed to the limits of thermal efficiency, owing to recent advancements in materials and cooling technologies. The hot section of a gas turbine engine works above the limits of material capabilities. Consequently, there is a high demand for cooling and sealing to assure safe and sound operation throughout the operational envelope of an engine. Secondary Air Systems (SAS) play a significant role in gas turbine engines to accomplish reliable operation of the individual modules as well as the whole engine. Main functions of SAS are to provide cooling flow to engine components, to seal bearing chambers (sumps) and to control bearing axial loads. Being a functional discipline, SAS owns the airflow that is essentially not the primary flowpath.

Traditionally, the design of secondary air systems utilized industrial friendly “one-dimensional modeling” for both compressible internal rotating/non-rotating fluid flow and heat transfer. Many correlations were developed to model/compute the flows with reasonable accuracy, taking into account of heat pickups on the way in flow circuits. Testing is an integral part of the design process comprising of flow testing of components, module testing and whole engine testing; providing essential data to characterize specific flow elements and circuits.

This collection invites papers that address the areas of SAS in gas turbine engines encompassing aviation, power generation and industrial applications. Of interest are papers that address novel approaches in flow network modeling, contemporary modeling and experimental efforts in rotor-stator/ rotor-rotor cavities, windage measurements and predictions, advanced flow network modeling to include transient behaviors, advanced sealing technologies, axial load control strategies, rim sealing developments and sump pressurization aspects.

Dr. Erinc Erdem
Guest Editor

Manuscript Submission Information

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Keywords

  • Gas turbine engines
  • Secondary air systems
  • Gas turbine sealing technologies
  • One-dimensional flow network modeling
  • Rotor-stator/rotor-rotor cavities
  • Compressible internal flows
  • Heat transfer Gas turbine engine testing

Published Papers (3 papers)

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Research

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Open AccessArticle Prediction of Heat Transfer in a Jet Cooled Aircraft Engine Compressor Cone Based on Statistical Methods
Received: 17 February 2018 / Revised: 12 April 2018 / Accepted: 16 April 2018 / Published: 1 May 2018
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Abstract
The paper presents the setup and analysis of an experimental study on heat transfer of a jet cooled compressor rear cone with adjacent conical housing. The main goal of the paper is to describe the systematic derivation of empirical correlations for global Nusselt
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The paper presents the setup and analysis of an experimental study on heat transfer of a jet cooled compressor rear cone with adjacent conical housing. The main goal of the paper is to describe the systematic derivation of empirical correlations for global Nusselt numbers to be used in the design process of a jet engine secondary air system. Based on the relevant similarity parameters obtained from literature, operating points are deduced leading to a full factorial design experiment to identify all effects and interactions. The varied similarity parameters are the circumferential Reynolds number, the non-dimensional mass flow, the non-dimensional spacing between rotor and stator, and the jet incidence angle. The range of the varied similarity parameters covers engine oriented operating conditions and is therefore suitable to predict Nusselt numbers in the actual engine component. In order to estimate measurement uncertainties, a simplified model of the test specimen, consisting of a convectively cooled flat plate, has been derived. Uncertainties of the measured quantities and derived properties are discussed by means of a linear propagation of uncertainties. A sensitivity study shows the effects of the input parameters and their interactions on the global Nusselt number. Subsequently, an empirical correlation for the global Nusselt numbers is derived using a multivariate non-linear regression. The quality of the empirical correlation is assessed by means of statistical hypotheses and by a comparison between measured and predicted data. The predicted values show excellent agreement with experimental data. In a wide range, accuracies of 15% can be reached when predicting global Nusselt numbers. Furthermore, the results of the sensitivity study show that pre-swirled cooling air does not have a positive effect on heat transfer. Full article
(This article belongs to the Special Issue Secondary Air Systems in Gas Turbine Engines)
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Open AccessArticle Numerical Investigation on Windback Seals Used in Aero Engines
Received: 16 November 2017 / Revised: 4 January 2018 / Accepted: 12 January 2018 / Published: 20 January 2018
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Abstract
Seals are considered one of the most important flow elements in turbomachinery applications. The most traditional and widely known seal is the labyrinth seal but in recent years other types like the brush or carbon seals were introduced since they considerably reduce the
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Seals are considered one of the most important flow elements in turbomachinery applications. The most traditional and widely known seal is the labyrinth seal but in recent years other types like the brush or carbon seals were introduced since they considerably reduce the sealing air consumption. When seals are used for sealing of aero engine bearing chambers they are subjected to high “bombardment” through oil particles which are present in the bearing chamber. These particles mainly result from the bearings as a consequence of the high rotational speeds. Particularly when carbon or brush seals are used, problems with carbon formation (coking) may arise when oil gets trapped in the very tight gap of these seals. In order to prevent oil migration into the turbomachinery, particularly when the pressure difference over a seal is small or even negligible, significant improvement can be achieved through the introduction of so called windback seals. This seal has a row of static helical teeth (thread) and below this thread a scalloped or smooth shaft section is rotating. Depending on the application, a windback seal can be used alone or as a combination with another seal (carbon, brush or labyrinth seal). A CFD analysis carried out with ANSYS CFX version 11 is presented in this paper with the aim to investigate this seal type. The simulations were performed by assuming a two-phase flow of air and oil in the bearing compartment. Design parameters like seal clearance, thread size, scallop width, were investigated at different operating conditions. Full article
(This article belongs to the Special Issue Secondary Air Systems in Gas Turbine Engines)
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Review

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Open AccessReview Buoyancy-Induced Heat Transfer inside Compressor Rotors: Overview of Theoretical Models
Received: 16 February 2018 / Revised: 12 March 2018 / Accepted: 13 March 2018 / Published: 17 March 2018
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Abstract
Increasing pressures in gas-turbine compressors, particularly in aeroengines where the pressure ratios can be above 50:1, require smaller compressor blades and an increasing focus on blade-clearance control. The blade clearance depends on the radial growth of the compressor discs, which in turn depends
[...] Read more.
Increasing pressures in gas-turbine compressors, particularly in aeroengines where the pressure ratios can be above 50:1, require smaller compressor blades and an increasing focus on blade-clearance control. The blade clearance depends on the radial growth of the compressor discs, which in turn depends on the temperature and stress in the discs. As the flow inside the disc cavities is buoyancy-driven, calculation of the disc temperature is a conjugate problem: the heat transfer from the disc is coupled with the air temperature inside the cavity. The flow inside the cavity is three-dimensional, unsteady and unstable, so computational fluid dynamics is not only expensive and time-consuming, it is also unable to achieve accurate solutions at the high Grashof numbers found in modern compressors. Many designers rely on empirical equations based on inappropriate physical models, and recently the authors have produced a series of papers on physically-based theoretical modelling of buoyancy-induced heat transfer in the rotating cavities found inside compressor rotors. Predictions from these models, all of which are for laminar flow, have been validated using measurements made in open and closed compressor rigs for a range of flow parameters representative of those found inside compressor rotors. (The fact that laminar buoyancy models can be used for large Grashof numbers (up to 10 12 ), where most engineers expect the flow to be turbulent, is attributed to the large Coriolis accelerations in the fluid core and to the fact that there is only a small difference between the rotational speed of the core and that of the discs.) As many as 223 separate tests were analysed in the validation of the models, and good agreement between the predictions and measurements was achieved for most of these cases. This overview paper has collected together the equations from these papers, which should be helpful to designers and research workers. The paper also points out the limitations of the models, all of which are for steady flow, and shows where further experimental evidence is needed. Full article
(This article belongs to the Special Issue Secondary Air Systems in Gas Turbine Engines)
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