Research Papers

A Path Toward the Aerodynamic Robust Design of Low Pressure Turbines

[+] Author and Article Information
Francesco Bertini

e-mail: francesco.bertini@aviogroup.com

Martina Credi

Avio S.p.A.
via I Maggio, 99, 10040,
Rivalta di Torino (TO), Italy

Matteo Giovannini

“Sergio Stecco” Department of Energy Engineering,
University of Florence,
via di Santa Marta,
Firenze, 3, 50139, Italy

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received June 28, 2012; final manuscript received August 21, 2012; published online November 2, 2012. Editor: David Wisler.

J. Turbomach 135(2), 021018 (Nov 02, 2012) (11 pages) Paper No: TURBO-12-1085; doi: 10.1115/1.4007519 History: Received June 28, 2012; Revised August 21, 2012

Airline companies are continuously demanding lower-fuel-consuming engines and this leads to investigating innovative configurations and to further improving single module performance. In this framework the low pressure turbine (LPT) is known to be a key component since it has a major effect on specific fuel consumption (SFC). Modern aerodynamic design of LPTs for civil aircraft engines has reached high levels of quality, but new engine data, after first engine tests, often cannot achieve the expected performance. Further work on the modules is usually required, with additional costs and time spent to reach the quality level needed to enter into service. The reported study is aimed at understanding some of the causes for this deficit and how to solve some of the highlighted problems. In a real engine, the LPT module works under conditions which differ from those described in the analyzed numerical model: the definition of the geometry cannot be so accurate, a priori unknown values for boundary conditions data are often assumed, complex physical phenomena are seldom taken into account, and operating cycle may differ from the design intent due to a nonoptimal coupling with other engine components. Moreover, variations are present among different engines of the same family, manufacturing defects increase the uncertainty and, finally, deterioration of the components occurs during service. Research projects and several studies carried out by the authors lead to the conclusion that being able to design a module whose performance is less sensitive to variations (robust LPT) brings advantages not only when the engine performs under strong off-design conditions but also, due to the abovementioned unknowns, near the design point as well. Concept and preliminary design phases are herein considered, highlighting the results arising from sensibility studies and their impact on the final designed robust configuration. Module performance is afterward estimated using a statistical approach.

Copyright © 2013 by ASME
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Fig. 1

Baseline cross section

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Fig. 2

Robustness index definition

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Fig. 3

Design process flow chart

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Fig. 4

Velocity triangles at midspan (baseline configuration)

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Fig. 5

Smith diagram for baseline configuration

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Fig. 6

Streamline definition for through-flow analysis

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Fig. 7

Robustness index versus Zweifel number for each row

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Fig. 10

Robustness index versus Mach ratio for each row

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Fig. 8

Cross section variation for aspect ratio sensitivity

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Fig. 9

Robustness index versus aspect ratio for each row

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Fig. 12

2D Spanwise DOE for exit flow angles

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Fig. 11

1D robust configuration versus baseline (in brackets)

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Fig. 19

Range on incidence angle deviations due to some real versus model variations

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Fig. 15

Isentropic Mach distributions for stage 3 (baseline versus final configuration)

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Fig. 21

Steady versus unsteady inlet flow angle

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Fig. 14

Robustness index during optimization phases

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Fig. 13

Q3D optimization of each parametric section

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Fig. 16

Efficiency at different rotational speeds

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Fig. 17

Final configuration efficiency gain

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Fig. 20

Effect of clearances and leakages on two adjacent rows (RTC tip zone)

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Fig. 22

Performance benefit of optimized configuration

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Fig. 18

Reynolds and turbulence level effects



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