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Finite Element Turbine Blade Tangling Modelling Following a Shaft Failure

[+] Author Affiliations
Aikaterini Psarra, Vassilios Pachidis, Pericles Pilidis

Cranfield University, Cranfield, Bedfordshire, UK

Paper No. GT2009-60144, pp. 73-81; 9 pages
doi:10.1115/GT2009-60144
From:
  • ASME Turbo Expo 2009: Power for Land, Sea, and Air
  • Volume 6: Structures and Dynamics, Parts A and B
  • Orlando, Florida, USA, June 8–12, 2009
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4887-6 | eISBN: 978-0-7918-3849-5
  • Copyright © 2009 by ASME

abstract

A shaft failure in a gas turbine engine is a severe event which leads to a sudden decoupling between the compressor and turbine, while there is not any instantaneous variation in the aerodynamic power flow. During a shaft failure event, the decoupled turbine is free to accelerate to a terminal speed whilst, depending on the arrangement of the shaft support bearings, the aerodynamic loads may also force it to move rearwards and contact the downstream NGV structure. If the terminal speed attained exceeds a certain critical limit, high energy debris may be released from the engine compromising the safety of the operations. In order to prove that shaft failure events can be handled in a safe and contained manner, engine manufacturers need to demonstrate among others that the extremely high rotational speeds a free running turbine can attain, can be reduced to a minimum value as quickly as possible. The present paper attempts to prove that one potential mechanism for limiting terminal speed may be blade tangling. Seal segments and platforms in particular can be designed in such a way so that they become quickly damaged and eroded by the dislocated turbine’s disc to allow for a quick contact between the turbine rotor blades and NGVs. A premature blade tangling can increase the energy dissipated as friction and heat between the structures and can lead to a decrease in terminal speed. The work reported here investigates this exact scenario focusing on a hypothetical intermediate pressure (IP) shaft failure of a modern 3-spool High By-pass Ratio (HBR) turbofan engine. The study investigates the effects of the various damage mechanisms considering the violent interaction of turbine structures using Finite Element Analysis (FEA). More specifically, the paper discusses analytically the development of a three-dimensional FEA model for the simulation of the dynamic impact phenomenon as well as the implementation of a dynamic non-linear finite element solver for the modelling of blade to vane interactions. A number of sample scenarios involving IPT blade to LP1 vane contact are presented to provide a better understanding of the effects of blade tangling on the evolution of the event. The study reported in this manuscript constitutes a first important step towards developing an appropriate simulation strategy for the modelling of turbine interactions following a shaft failure event. It seeks to advance today’s knowledge in the evolution of such complex events and the effects on turbine terminal speed of blade tangling and energy dissipated in eroding/melting surrounding structures.

Copyright © 2009 by ASME

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