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Impact of a cooled cooling air installation on the external aerodynamics of a gas turbine combustion system

conference contribution
posted on 2015-10-19, 14:03 authored by Duncan WalkerDuncan Walker, Liang Guo
The trend for higher overall pressure ratios means that turbine entry temperatures are continually increasing. Furthermore, the development of lean, low-emission combustion systems reduces the availability of cooling air and is accompanied by new problems at the combustor/turbine interface. For example, the exit temperature traverse differs from that found in traditional rich-burn combustors with increased swirl and a much flatter profile. Effectively cooling the turbine components is becoming increasingly difficult. One solution is to employ cooled cooling air (CCA) where some of the compressor efflux is diverted for additional cooling in a heat exchanger located in the by-pass duct. An example CCA system is presented which includes an off-take within the dump cavity and the addition of radial struts within the pre-diffuser through which the cooled air is returned to the engine core. This paper addresses the impact this CCA system has on the combustion system external aerodynamics. This included the development of a fully annular, isothermal test facility which incorporated a bespoke 1.5 stage axial compressor, engine relevant outlet guide vanes, pre-diffuser and combustor geometry. A datum aerodynamic performance was established for a non-CCA configuration with a clean, un-strutted prediffuser. Results for this baseline CCA system demonstrated that inclusion of a bleed in the dump cavity had limited effect on the overall flow field. However, the inclusion of struts within the pre-diffuser caused a reduction in area ratio and a notable increase in system loss. Consequently an alternative pre-diffuser was designed (using CFD) with the aim of increasing the area ratio back to that of the un-strutted datum. A so-called hybrid diffuser was designed in which the CCA bleed was moved to the pre-diffuser outer wall. The bleed was then used to re-energize the boundary layer, preventing flow separation, enabling the area ratio to be increased close to the datum value. The mechanisms of the hybrid diffuser are complex; the geometry of the off-take and its location with respect to the OGV and strut leading edge were seen to be critical. Experimental evaluation of the final design demonstrated the effective operation the hybrid diffuser with the result that the system loss returned to a level close to that of the datum. Only small differences were seen in the overall flow field.

Funding

The research leading to these results was undertaken as part of the IMPACT_AE project (Intelligent Design Methodologies for Low Pollutant Combustors for Aero-Engines). This was cofunded by Rolls-Royce plc. and the European Commission within the 7th Framework Program FP7-265586).

History

School

  • Aeronautical, Automotive, Chemical and Materials Engineering

Department

  • Aeronautical and Automotive Engineering

Published in

Proceedings of ASME Turbo Expo

Citation

WALKER, A.D. and GUO. L., 2015. Impact of a cooled cooling air installation on the external aerodynamics of a gas turbine combustion system. IN: ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 4B: Combustion, Fuels and Emissions Montreal, June 15–19, GT2015-43186.

Publisher

© Rolls-Royce plc. Published by ASME.

Version

  • VoR (Version of Record)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Publication date

2015

Notes

This paper is in closed access.

ISBN

9780791856697

Language

  • en

Location

Montreal, Canada

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