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Research Papers

Analysis of Unsteady Tip and Endwall Heat Transfer in a Highly Loaded Transonic Turbine Stage

[+] Author and Article Information
Vikram Shyam

 NASA Glenn Research Center, Cleveland, OH 44135

Ali Ameri

 NASA Glenn Research Center, Cleveland, OH 44135; Ohio State University, Columbus, OH 44135

Jen-Ping Chen

Aerospace Engineering, Ohio State University, Columbus, OH 44135

J. Turbomach 134(4), 041022 (Jul 25, 2011) (9 pages) doi:10.1115/1.4003719 History: Revised September 12, 2010; Received November 02, 2010; Published July 25, 2011; Online July 25, 2011

In a previous study, vane-rotor shock interactions and heat transfer on the rotor blade of a highly loaded transonic turbine stage were simulated. The geometry consists of a high pressure turbine vane and a downstream rotor blade. This study focuses on the physics of flow and heat transfer in the rotor tip, casing, and hub regions. The simulation was performed using the unsteady Reynolds-averaged Navier–Stokes code MSU-TURBO . A low Reynolds number k-ε model was utilized to model turbulence. The rotor blade in question has a tip gap height of 2.1% of the blade height. The Reynolds number of the flow is approximately 3×106/m. Unsteadiness was observed at the tip surface that results in intermittent “hot spots.” It is demonstrated that unsteadiness in the tip gap is governed by inviscid effects due to high speed flow and is not strongly dependent on pressure ratio across the tip gap contrary to published observations that have primarily dealt with subsonic tip flows. The high relative Mach numbers in the tip gap lead to a choking of the leakage flow that translates to a relative attenuation of losses at higher loading. The efficacy of new tip geometry is discussed to minimize heat flux at the tip while maintaining choked conditions. In addition, an explanation is provided that shows the mechanism behind the rise in stagnation temperature on the casing to values above the absolute total temperature at the inlet. It is concluded that even in steady (in a computational sense) mode, work transfer to the near tip fluid occurs due to relative shearing by the casing. This is believed to be the first such explanation of the work transfer phenomenon in the open literature. The difference in pattern between steady and time-averaged heat fluxes at the hub is also explained.

Copyright © 2012 by American Society of Mechanical EngineersThe United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable worldwide license to publish or reproduce the published form of this work, or allows others to do so, for United States Government purposes.
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References

Figures

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Figure 1

Rotor blade surface and hub surface mesh (2)

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Figure 2

Boundary conditions for unsteady simulation (2)

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Figure 3

Grid in the tip region of rotor

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Figure 4

Grid in the tip region of rotor

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Figure 5

Tip Stanton number comparison between CFD and experiment

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Figure 6

Time-averaged tip Stanton number

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Figure 7

Plane 1 on the tip surface

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Figure 8

Zoomed in view of separated zone in Fig. 7

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Figure 9

Plane 2 on the tip surface

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Figure 10

Compressions and expansions in the tip gap (on Plane 1)

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Figure 11

Discovery of unsteady hot spot (snapshot of video)

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Figure 12

Tip gap during hot spot

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Figure 13

Tip gap before hot spot

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Figure 14

Streamlines through the tip gap before (top) and during (bottom) the hot spot

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Figure 15

Hub Stanton number for steady (top) and time-averaged (bottom) simulations (2)

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Figure 16

Hub Stanton number: comparison between CFD and experiment (2)

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Figure 17

Hub boundary layer shape at the rotor inlet, characterized by vorticity magnitude (2)

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Figure 18

Stanton number on rotor casing for steady (top) and time-averaged (bottom) unsteady simulations (12)

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