Research Papers

Designing Low Pressure Turbines for Optimized Airfoil Lift

[+] Author and Article Information
Jochen Gier, Matthias Franke, Norbert Hübner, Thomas Schröder

 MTU Aero Engines GmbH, Munich D-80995, Germany

J. Turbomach 132(3), 031008 (Mar 25, 2010) (12 pages) doi:10.1115/1.3148476 History: Received September 01, 2008; Revised April 01, 2009; Published March 25, 2010; Online March 25, 2010

In the past 10–15 years, substantial effort has been spent on increasing the airfoil lift especially in aero-engine low pressure turbines. This has been attractive, since increased airfoil lift can be used for airfoil count decrease leading to weight and hardware cost reduction. The challenge with this effort consequently has been to keep the efficiency at high levels. Depending on the baseline level of airfoil lift, an increase of 20–50% has been realized and at least partly incorporated in modern turbine designs. With respect to efficiency there is actually an optimum level of airfoil lift. Airfoil rows at a lift level below this optimum suffer from an excessive number of airfoils with too much wetted surface and especially increasing trailing edge losses. Airfoils at lift levels above this optimum suffer from growing losses due to high peak Mach numbers inside the airfoil row, higher rear diffusion on the airfoil suction sides, and increased secondary flow losses. Since fuel cost have been rising significantly, as has been the awareness of the environmental impact of CO2, it becomes more and more important to design low pressure turbines for an optimal trade between efficiency and weight to achieve the lowest engine fuel burn. This paper summarizes work done recently and in the past to address the main influences and mechanisms of the airfoil lift level, with respect to losses and efficiency as a basis for determination of optimal airfoil lift selection.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Pressure coefficient in T106 cascade for 3 pitch: chord ratios (A, B, and C) (42)

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Figure 2

Diagrams for optimal pitch to chord ratio from Ref. 40 top and from Ref. 41 bottom

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Figure 3

Loss coefficient in T106 cascade (midspan) for three pitch: chord ratios (A, B, and C) (42)

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Figure 4

Pressure distribution for baseline (T160) and two high lift cascades (T161 and T162), Re=200k, with periodic wakes at inlet

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Figure 5

Comparison of loss coefficient at midspan for baseline (T160) and two high lift cascades (T161 and T162), inflow with wakes

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Figure 6

Total pressure loss for baseline (T160) and two high lift cascades (T161 and T162) 40% downstream of the trailing edge

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Figure 7

Total pressure loss (reference T160 total loss) for baseline (T160) and two high lift cascades (T161 and T162), Re=200k

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Figure 8

Secondary kinetic energy comparison between T160 and two high lift cascades, T161 and T162, Re=200k, half span

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Figure 9

Turbine efficiency versus normalized Reynolds number for HL and UHL blading from Ref. 21

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Figure 10

General arrangement of MTU-A turbine rig, build D02

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Figure 11

Midspan surface pressure distribution for middle vane V2 in MTU-A turbine, comparison of baseline (N138) and high lift (N111), measurement (symbols), and CFD (lines)

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Figure 12

Efficiency for 100% and 80% speed lines for MTU-A turbine, comparison of baseline D01, and high lift D02 builds

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Figure 13

Turbine efficiency versus Reynolds number (first vane) for MTU-A, comparison of baseline D01, D01_V2%–20%, and high lift D02 build, n/nd=100%

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Figure 14

General arrangement of five-stage rig, modified airfoil rows for build B02

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Figure 15

Operating map of five-stage rig, comparison of build B01 and build B02

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Figure 16

Surface pressure distribution for Rig MTU-B, Vane 4, for 100% speed and 80% speed, Re=design

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Figure 17

Turbine efficiency versus span in MTU-B, sensitivity to speed (left), and Reynolds number (right)

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Figure 18

Secondary kinetic energy change for MTU-B, V4, reference B01 black, high lift B02 light

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Figure 19

Reynolds lapse of five-stage rig, comparison of build B01 and build B02

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Figure 20

Flow visualization in fourth vane, rig MTU-B

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Figure 21

Efficiency drop predicted by CFD for MTU-B turbine for designs with different average Zweifel coefficients




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