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Research Papers: Gas Turbines: Aircraft Engine

Aerodynamic Design of Separate-Jet Exhausts for Future Civil Aero-engines—Part I: Parametric Geometry Definition and Computational Fluid Dynamics Approach

[+] Author and Article Information
Ioannis Goulos

Propulsion Engineering Centre,
Cranfield University,
Bedfordshire, MK430AL, UK
e-mail: i.goulos@cranfield.ac.uk

Tomasz Stankowski

Propulsion Engineering Centre,
Cranfield University,
Bedfordshire, MK430AL, UK
e-mail: t.stankowski@cranfield.ac.uk

John Otter

Propulsion Engineering Centre,
Cranfield University,
Bedfordshire, MK430AL, UK
e-mail: j.j.otter@cranfield.ac.uk

David MacManus

Propulsion Engineering Centre,
Cranfield University,
Bedfordshire, MK430AL, UK
e-mail: D.G.Macmanus@cranfield.ac.uk

Nicholas Grech

Installation Aerodynamics,
Rolls-Royce plc,
Trent Hall 2.2, SinA-17,
Derby DE24 8BJ, UK
e-mail: Nicholas.Grech@Rolls-Royce.com

Christopher Sheaf

Installation Aerodynamics,
Rolls-Royce plc,
Trent Hall 2.2, SinA-17,
Derby DE24 8BJ, UK
e-mail: Christopher.Sheaf@Rolls-Royce.com

Contributed by the Aircraft Engine Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 22, 2015; final manuscript received December 18, 2015; published online March 15, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(8), 081201 (Mar 15, 2016) (14 pages) Paper No: GTP-15-1538; doi: 10.1115/1.4032649 History: Received November 22, 2015; Revised December 18, 2015

This paper presents the development of an integrated approach which targets the aerodynamic design of separate-jet exhaust systems for future gas-turbine aero-engines. The proposed framework comprises a series of fundamental modeling theories which are applicable to engine performance simulation, parametric geometry definition, viscous/compressible flow solution, and design space exploration (DSE). A mathematical method has been developed based on class-shape transformation (CST) functions for the geometric design of axisymmetric engines with separate-jet exhausts. Design is carried out based on a set of standard nozzle design parameters along with the flow capacities established from zero-dimensional (0D) cycle analysis. The developed approach has been coupled with an automatic mesh generation and a Reynolds averaged Navier–Stokes (RANS) flow-field solution method, thus forming a complete aerodynamic design tool for separate-jet exhaust systems. The employed aerodynamic method has initially been validated against experimental measurements conducted on a small-scale turbine powered simulator (TPS) nacelle. The developed tool has been subsequently coupled with a comprehensive DSE method based on Latin-hypercube sampling. The overall framework has been deployed to investigate the design space of two civil aero-engines with separate-jet exhausts, representative of current and future architectures, respectively. The inter-relationship between the exhaust systems' thrust and discharge coefficients has been thoroughly quantified. The dominant design variables that affect the aerodynamic performance of both investigated exhaust systems have been determined. A comparative evaluation has been carried out between the optimum exhaust design subdomains established for each engine. The proposed method enables the aerodynamic design of separate-jet exhaust systems for a designated engine cycle, using only a limited set of intuitive design variables. Furthermore, it enables the quantification and correlation of the aerodynamic behavior of separate-jet exhaust systems for designated civil aero-engine architectures. Therefore, it constitutes an enabling technology toward the identification of the fundamental aerodynamic mechanisms that govern the exhaust system performance for a user-specified engine cycle.

Copyright © 2016 by Rolls-Royce plc
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Figures

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Fig. 1

Notional axisymmetric housing geometry for a very-high bypass ratio (VHBR) turbofan engine with separate-jet exhausts

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Fig. 2

Upper-level overview of the developed software architecture

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Fig. 3

Individual terms comprising Bernstein's polynomial for n = 8

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Fig. 4

Employed parameters for the parametric geometry representation of an exhaust system: (a) duct geometry and (b) nozzle geometry

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Fig. 5

Employed CFD domain and BCs

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Fig. 6

Mesh generation and topology definition: (a) overall view of derived computational mesh and (b) mesh close-up

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Fig. 7

Graphical illustration of force accounting for the computation of gross propulsive force FGexhaust

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Fig. 8

Engine model used for the grid sensitivity analysis: (a) model geometry, (b) computational mesh, Ncell≈4.76×105, and (c) Mach number contours at midcruise conditions, M∞=0.85, Alt.=13106.4m

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Fig. 9

Grid sensitivity analysis for the described engine model: (a) bypass nozzle discharge coefficient CDBypass, (b) core nozzle discharge coefficient CDCore, and (c) overall exhaust velocity coefficient CVOverall

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Fig. 10

Comparison of predicted nozzle performance parameters with experimental data reported in Ref. [34]: (a) normalized bypass nozzle mass flow m˙bypass/m˙bypassref, gross propulsive force FG

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Fig. 11

Model validation: (a) Mach number contours for FPR = 1.6, M∞=0.17, (b) isentropic Mach number Misen on the bypass and core nozzle inner walls—comparison with experimental data from Ref. [34]

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Fig. 12

2D axisymmetric geometries of investigated engine architectures: (a) design representative of future engine architectures (E1) and (b) design representative of current engine architectures (E2)

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Fig. 13

Mach number contours for the baseline exhaust system designs at DP midcruise conditions: (a) design representative of future engine architectures (E1) and (b) design representative of current engine architectures (E2)

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Fig. 14

Design space definition: (a) bypass duct outer line position ybpout=Rbpout/Lductin, (b) ybpin=Rbpin/Lductin, (c) nozzle CP to exit area ratio Aratio=ACP/Aexit and length ratio κlenin=LinNozzle/h2, (d) outer line slope at the CP θCPout, (e) CP inner/outer curvature radius ratio κCPin/out=RcurveCP,in/out/h2, (f) core cowl length lcrcowl=Lcrcowl/Rfan, (g) zone 3 vent exit position lz3exit=Lz3exit/Lcrcowl, (h) zone 3 exit Mach no. Mz3exit, and (i) core cowl angle θcrcowl and outer line angle θnozzleout

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Fig. 15

Correlation of performance metrics for the future E1engine: (a) CDBypass and CVOverall, (b) CDBypass and FN, and (c) CVOverall and FN

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Fig. 16

Correlation of performance metrics for the current E2engine: (a) CDBypass and CVOverall, (b) CDBypass and FN, and (c) CVOverall and FN

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Fig. 17

Linear correlation estimation between design variables and performance metrics: (a) future E1 engine and (b) current E2 engine

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Fig. 18

Exhaust design improvement for the E1 future engine architecture: (a) baseline exhaust nozzle and (b) improved exhaust nozzle

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