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Research Papers

Shorten the Intermediate Turbine Duct Length by Applying an Integrated Concept

[+] Author and Article Information
A. Marn

Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology, Graz 8010, Austriaandreas.marn@tugraz.at

E. Göttlich, H. P. Pirker

Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology, Graz 8010, Austria

D. Cadrecha1

Aerothermal Department, Industria de Turbopropulsores S.A., Madrid, Spain

1

Also at Aerothermal Department, Industria de Turbopropulsores S.A., Madrid, Spain.

J. Turbomach 131(4), 041014 (Jul 06, 2009) (10 pages) doi:10.1115/1.3070578 History: Received August 22, 2008; Revised October 01, 2008; Published July 06, 2009

The demand of further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters, which rotate at lower speed. Therefore, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at larger diameters minimizing the losses and providing an adequate flow at the low pressure (LP)-turbine inlet. Due to costs and weight, this intermediate turbine duct has to be as short as possible. This would lead to an aggressive (high diffusion) s-shaped duct geometry. It is possible to shorten the duct simply by reducing the length but the risk of separation is rising and losses increase. Another approach to shorten the duct and thus the engine length is to apply a so called integrated concept. These are novel concepts where the struts, mounted in the transition duct, replace the usually following LP-vane row. This configuration should replace the first LP-vane row from a front bearing engine architecture where the vane needs a big area to hold bearing services. That means the rotor is located directly downstream of the strut. This means that the struts have to provide the downstream blade row with undisturbed inflow with suitable flow angle and Mach number. Therefore, the (lifting) strut has a distinct three-dimensional design in the more downstream part, while in the more upstream part, it has to be cylindrical to be able to lead through supply lines. In spite of the longer chord compared with the base design, this struts have a thickness to chord ratio of 18%. To apply this concept, a compromise must be found between the number of struts (weight), vibration, noise, and occurring flow disturbances due to the secondary flows and losses. The struts and the outer duct wall have been designed by Industria de Turbopropulsores. The inner duct was kept the same as for the base line configuration (designed by Motoren und Turbinen Union). The aim of the design was to have similar duct outflow conditions (exit flow angle and radial mass flow distribution) as the base design with which it is compared in this paper. This base design consists of a single transonic high pressure (HP)-turbine stage, an aggressive s-shaped intermediate turbine duct, and a LP-vane row. Both designs used the same HP-turbine and were run in the continuously operating Transonic Test Turbine Facility at Graz University of Technology under the same engine representative inlet conditions. The flow field upstream and downstream the LP-vane and the strut, respectively, has been investigated by means of five hole probes. A rough estimation of the overall duct loss is given as well as the upper and lower weight reduction limit for the integrated concept.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 4

Mass averaged total pressure distribution in plane C

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Figure 5

Area averaged static pressure distribution in plane C

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Figure 6

Mass averaged yaw angle distribution in plane C

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Figure 7

Mach number distribution in plane C, base design

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Figure 8

Yaw angle distribution in plane C, base design

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Figure 9

Mach number distribution in plane C for the IC

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Figure 10

Yaw angle distribution in plane C for the IC

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Figure 11

Mass averaged Mach number distribution in plane E

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Figure 12

Mass averaged total pressure distribution in plane E

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Figure 13

Area averaged static pressure distribution in plane E

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Figure 14

Mass averaged yaw angle distribution in plane E

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Figure 15

Total pressure ratio distribution of the base design

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Figure 16

Mach number distribution of the base design

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Figure 17

Yaw angle distribution of the base design

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Figure 18

Total pressure ratio distribution of the IC

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Figure 19

Mach number distribution of the IC

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Figure 20

Yaw angle distribution of the IC

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Figure 21

Oil coating before the surfaces are exposed to the flow

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Figure 22

Picture of the outer duct wall

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Figure 23

Picture of the inner duct wall

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Figure 24

Oil flow visualization on Suction Surface

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Figure 25

Oil flow visualization on the pressure side

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Figure 26

Static pressure rise coefficient

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Figure 1

Meridional section with probe measurement planes (a), blade counts and profiles (b), and definition of nondimensional duct length l/hexit,blade=2 (c) for the base design

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Figure 2

Meridional section with probe measurement planes (a), and blade counts and profiles (b) for the integrated concept

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Figure 3

Mass averaged Mach number distribution in plane C

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