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Research Papers

Influence of Backward- and Forward-Facing Steps on the Flow Through a Turning Mid Turbine Frame

[+] Author and Article Information
Sabine Bauinger

Institute for Thermal Turbomachinery
and Machine Dynamics,
Graz University of Technology,
Graz 8010, Austria
e-mail: sabine.bauinger@tugraz.at

Emil Goettlich, Franz Heitmeir

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

Franz Malzacher

MTU Aero Engines,
Munich 80995, Germany

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 18, 2017; final manuscript received August 23, 2017; published online September 26, 2017. Editor: Kenneth Hall.

J. Turbomach 139(12), 121005 (Sep 26, 2017) (10 pages) Paper No: TURBO-17-1120; doi: 10.1115/1.4037859 History: Received August 18, 2017; Revised August 23, 2017

For this work, reality effects, more precisely backward-facing steps (BFSs) and forward-facing steps (FFSs), and their influence on the flow through a two-stage two-spool turbine rig under engine-relevant conditions were experimentally investigated. The test rig consists of an high pressure (HP) and an low pressure (LP) stage, with the two rotors rotating in opposite direction with two different rotational speeds. An S-shaped transition duct, which is equipped with turning struts (so-called turning mid turbine frame (TMTF)) and making therefore a LP stator redundant, connects both stages and leads the flow from a smaller to a larger diameter. This test setup allows the investigation of a TMTF deformation, which occurs in a real aero-engine due to non-uniform warming of the duct during operation—especially during run up—and causes BFSs and FFSs in the flow path. This happens for nonsegmented ducts, which are predominantly part of smaller engines. In the case of the test rig, steps were not generated by varying temperature but by shifting the TMTF in horizontal direction while the rotor and its casing were kept in the same position. In this way, both BFSs and FFSs between duct endwalls and rotor casing could be created. In order to avoid steps further downstream of the interface between HP rotor and TMTF, the complete aft rig was moved laterally too. In this case, the aft rig incorporates among others the LP rotor, the LP rotor casing, and the deswirler downstream of the LP stage. In order to catch the influence of the steps on the whole flow field, 360 deg rake traverses were performed downstream of the HP rotor, downstream of the duct, and downstream of the LP rotor with newly designed, laser-sintered combi-rakes for the measurement of total pressure and total temperature. Only the compact design of the rakes, which can be easily realized by additive manufacturing, makes the aforementioned 360 deg traverses in this test rig possible and allows a number of radial measurements positions, which is comparable to those of a five-hole probe. To get a more detailed information about the flow, also five-hole probe measurements were carried out in three measurement planes and compared to the results of the combi-rakes.

Copyright © 2017 by ASME
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References

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Figures

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Fig. 1

Cross section through TTTF including the measurement planes

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Fig. 2

Details of backward- and forward-facing steps; right picture shows the right half of the concerned test section; the left picture, the left one

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Fig. 3

Different views of a rake showing the alignment of the kielheads with the flow in terms of yaw and pitch angle and comparison with rake 2 highlighting the reference Kielhead

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Fig. 4

Comparison of pressure coefficient (radial line) between five-hole probe and combi-rakes for all measurement planes

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Fig. 5

360 Deg rake traverses for the basic setup in planes C, E, and F with 5 HP sector marked black

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Fig. 6

A 360 deg rake traverse for the setup with laterally shifted TMTF in planes C, E, and F pointing out where backward- and forward-facing steps were generated

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Fig. 7

Pressure coefficient in plane C resulting from 5HP measurements; comparison between basic and shifted setup

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Fig. 8

Pressure coefficient in plane C resulting from rake measurements; comparison between basic and shifted setup at maximum steps

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Fig. 9

Comparison of yaw angle in plane c resulting from 5HP measurements (radial line); sketch of effective flow area (right side)

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Fig. 10

Velocity triangles and circumferential velocity comparing both setups in plane C

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Fig. 11

Pressure coefficient in plane E resulting from 5HP measurements; comparison between basic and shifted setup

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Fig. 12

Oil flow visualization focusing on the outer casing for basic and shifted setup

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Fig. 13

Yaw angle in plane E resulting from 5HP measurements; comparison between basic and shifted setup

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Fig. 14

Power of the LP turbine for basic and shifted setup

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Fig. 15

Pressure coefficient in plane f resulting from 5HP measurements; comparison between basic and shifted setup

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