Research Papers

Modulation and Radial Migration of Turbine Hub Cavity Modes by the Rim Seal Purge Flow

[+] Author and Article Information
R. Schädler

Laboratory for Energy Conversion,
Department of Mechanical
and Process Engineering,
ETH Zurich,
Sonneggstrasse 3,
Zurich CH-8092, Switzerland
e-mail: schaedler@lec.mavt.ethz.ch

A. I. Kalfas

Department of Mechanical Engineering,
Aristotle University of Thessaloniki,
Thessaloniki GR-54124, Greece
e-mail: akalfas@auth.gr

R. S. Abhari

Laboratory for Energy Conversion,
Department of Mechanical
and Process Engineering,
ETH Zurich,
Sonneggstrasse 3,
Zurich CH-8092, Switzerland
e-mail: abhari@lec.mavt.ethz.ch

G. Schmid

Siemens AG,
Mellinghofer Str. 55,
Muelheim an der Ruhr D-45473, Germany
e-mail: gregor.schmid@siemens.com

S. Voelker

Siemens AG,
Mellinghofer Str. 55,
Muelheim an der Ruhr D-45473, Germany
e-mail: voelker.stefan@siemens.com

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 18, 2016; final manuscript received August 2, 2016; published online September 20, 2016. Editor: Kenneth Hall.The content of this paper is copyrighted by Siemens Energy, Inc. and is licensed to ASME for publication and distribution only. Any inquiries regarding permission to use the content of this paper, in whole or in part, for any purpose must be addressed to Siemens Energy, Inc. directly.

J. Turbomach 139(1), 011011 (Sep 20, 2016) (10 pages) Paper No: TURBO-16-1161; doi: 10.1115/1.4034416 History: Received July 18, 2016; Revised August 02, 2016

In the present paper, the results of an experimental and numerical investigation of the hub cavity modes and their migration into the main annulus flow are presented. A one-and-a-half stage, unshrouded and highly loaded axial turbine configuration with three-dimensionally shaped blades and cylindrical end walls has been tested in an axial turbine facility. Both the blade design and the rim seal purge flow path are representative to modern high-pressure gas turbines. The unsteady flow field at the hub cavity exit region has been measured with the fast-response aerodynamic probe (FRAP) for two different rim seal purge flow rates. Furthermore, fast-response wall-mounted pressure transducers have been installed inside the cavity. Unsteady full-annular computational fluid dynamics (CFD) simulations have been employed in order to complement the experimental work. The time-resolved pressure measurements inside the hub cavity reveal clear cavity modes, which show a strong dependency on the injected amount of rim seal purge flow. The numerical predictions provide information on the origin of these modes and relate them to pronounced ingestion spots around the circumference. The unsteady probe measurements at the rim seal interface show that the signature of the hub cavity induced modes migrates into the main annulus flow up to 30% blade span. Based on that, an aerodynamic loss mechanism has been found, showing that the benefit in loss reduction by decreasing the rim seal purge flow rate is weakened by the presence of turbine hub cavity modes.

Copyright © 2017 by Siemens Energy Inc.
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Grahic Jump Location
Fig. 1

Schematics of rim seal purge flow path (left) and close-up view of rotor upstream rim seal (right)

Grahic Jump Location
Fig. 2

FRAP probe tip schematic (left) and measurement location (right) of inclined probe measurements R in tilted (dash-dot line) and hub cavity absolute wall pressure transducers (spot). The position of axial slice for CFD normalized static pressure is indicated.

Grahic Jump Location
Fig. 3

Experimentally determined pressure frequency spectra for four different injection rate cases inside the hub cavity at −12% span

Grahic Jump Location
Fig. 4

Measured incremental increase of sound pressure level SPL (dB) induced by the cavity modes with respect to the suppressed cavity mode case IR3 = 1.2% inside the hub cavity

Grahic Jump Location
Fig. 5

Predicted pressure frequency spectrum for two rim seal purge flow injection rates at−12% span inside the hub cavity: IR0 = 0.0% (left) and IR2 = 0.8% (right)

Grahic Jump Location
Fig. 6

Instantaneous map of predicted normalized static pressure (-) over the full-annulus for IR0 = 0.0% and IR2 = 0.8%, indication of 8 (IR0 = 0.0%) and 22 (IR2 = 0.8%) low static pressure zones inside the hub cavity

Grahic Jump Location
Fig. 7

Close-up view of meridional slice through local low static pressure zone (slices 1 and 3, left) and between two low pressure zones (slices 2 and 4, right) for IR0 and IR2 superimposed with normalized radial velocity contour (-) and hub cavity stream lines

Grahic Jump Location
Fig. 8

Time-averaged rms of p′1 (Pa) in stationary frame of reference at R in tilted plane: (a) IR2 = 0.8%, (b) IR3 = 1.2%, and (c) relative change of rms p′1 (-) by increasing IR2 to IR3

Grahic Jump Location
Fig. 9

Time-averaged axial vorticity (Hz): (a) IR2 = 0.8% and (b) IR3 = 1.2%. Indication of secondary flow structures: trailing edge shed vortex (TESV) and stator 1 hub passage vortex (HPV).

Grahic Jump Location
Fig. 10

Pressure spectral analysis at three spanwise positions and stator pitch 0.5 for rim seal purge flow IR2 = 0.8% (left column, left) and IR3 = 1.2% (right column)

Grahic Jump Location
Fig. 11

Time-averaged total pressure loss coefficient Y (-) in stationary frame of reference at R in tilted plane: (a) IR2 = 0.8% and (b) IR3 = 1.2%

Grahic Jump Location
Fig. 12

Space time plot of total pressure loss coefficient Y (-) at 10% blade span: (a) IR2 = 0.8%, (b) IR3 = 1.2%, and (c) 2D representation at 0.5 stator pitch and 10% span for six consecutive rotor blade passing events



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