The amount of air drawn by the secondary air system (SAS) from the main gas path, although necessary, impairs the engine performance because it does not contribute to engine thrust. In order to quantify and minimize this pernicious effect, the usual practice is to model the air system with one-dimensional network solvers where the net nodes represent the various components of the system. For usual engine transients, it is sufficient to analyse the system performance with a quasi-steady approach because the time constant of the air system is two orders of magnitude smaller than the turbomachinery characteristic time. Nonetheless, the rapid changes that occur during certain transient or failure scenarios – particularly shaft failure events – call for a different approach to calculate the air system performance and the fluctuations of the turbomachinery endloads. However, there is no such approach available in the open literature to predict the transient response of the system. For steady-state conditions, the differential equations that govern the fluid evolution are not time discretized and thus can be solved in a relatively straightforward fashion. Moreover, unlike during transients, the flow is not supposed to reach sonic conditions anywhere within the network and, more importantly, flow reversal is not expected to occur.
The aim of this study is to develop a model for gas turbine SAS dynamics capable of tackling the sudden changes in the flow properties that occur within the system in the rapid transient scenarios. The whole system is initially broken down into a series of chambers of a finite volume connected by pipes that are initially modelled in isolation and then interconnected. The single-component models and their assembly are successfully validated against numerical and experimental data. The resultant modular tool constitutes a baseline into which further improvements and modifications can be integrated in subsequent works.
The usefulness of the computational tool is demonstrated through the analysis of the flow evolution within the SAS and the subsequent turbine endload during a shaft failure event.
Time accurate modelling of the secondary air system response to rapid transients
2011-08-01
13 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
Time accurate modelling of the secondary air system response to rapid transients
Online Contents | 2011
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