22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-6.8.1

THE NUMERICAL SIMULATION AND EXPERIMENTAL VALIDATION OF VENTILATION FLOW AND FIRE EVENTS IN A TRENT NACELLE FIRE ZONE

A. J. Mullender (1), M. H. Coney (1), D. M. Horrocks (2), J. J. McGuirk (3), J. B. Moss (4), P. A. Rubini (4), C. D. Stewart (4), D. Binks (4)
(1) Rolls-Royce plc, Derby, UK; (2) CPS, Universidad de Zaragoza, LITEC, Maria de Luna, 3, 50015, Zaragoza, Spain; (3) Department of Aeronautical and Automotive Engineering and Transport Studies, Loughborough University, Leicestershire, UK; (4)School of Mechanical Engineering, Cranfield University, Bedford, UK.

Keywords: engine, fire, ventilation, certification.

Design for aircraft engine zone ventilation and fire certification has traditionally been driven by practical demonstration using standardised tests. For large structures in particular, the cost of carrying out such tests can become prohibitively expensive. Numerical simulation provides the opportunity to investigate structure and component performance both during normal operation and in the event of fire and thereby promote greater integrated design. One of the major problems in any numerical simulation of a complex geometrical system is obtaining a suitable representation of the geometry to be used in the simulation process - in this case structured and unstructured grid generation and Computational Fluid Dynamics (CFD) analysis. With current Computer Aided Design (CAD) practises, the geometry is not in a suitable form and with large datasets such as those used here, the problems are often exacerbated. The challenges associated with the identification of a suitable geometry subset from the full engine assembly tree, filtering of unusable detail and additional CAD preparation for the grid generation are addressed. The realisation of tractable but representative geometries is illustrated by examples characteristic of the Trent engine family. The numerical simulations focus on the capture of the key physical processes. During normal operation this encompasses the ram inlet zone ventilation flow, including heat transfer from engine casings and accessories, whilst for a fire event this will additionally include the interaction with the buoyantly driven fire plume. The scenario investigated in this paper is that of a burner-simulated gearbox fire. Predictions of the internal velocity field, gas temperatures and composition and wall heat fluxes are compared with experimental measurements on a ½ scale nacelle fire test rig and, for the ventilation flow, with visualisation using dye and bubble tracers in a Perspex model of similar scale by water analogy. The numerical simulations capture important features of this complex flowfield and are shown to identify a number of distinct opportunities for design refinement.

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