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Research Papers

Experimental Study of Ingestion in the Rotor–Stator Disk Cavity of a Subscale Axial Turbine Stage

[+] Author and Article Information
J. Balasubramanian

Mechanical and Aerospace Engineering,
Arizona State University,
Tempe, AZ 85287
e-mail: jbalasu1@asu.edu

P. S. Pathak

Mechanical and Aerospace Engineering,
Arizona State University,
Tempe, AZ 85287
e-mail: pspathak@asu.edu

J. K. Thiagarajan

Mechanical and Aerospace Engineering,
Arizona State University,
Tempe, AZ 85287
e-mail: jthiagar@asu.edu

P. Singh

Mechanical and Aerospace Engineering,
Arizona State University,
Tempe, AZ 85287
e-mail: psingh28@asu.edu

R. P. Roy

Fellow ASME
Mechanical and Aerospace Engineering,
Arizona State University,
Tempe, AZ 85287
e-mail: ramendra.roy@asu.edu

A. V. Mirzamoghadam

Fellow ASME
Honeywell Aerospace,
Phoenix, AZ 85034
e-mail: Alexander.Mirzamoghadam@honeywell.com

As explained later, the static pressure in the radially inner part of the seal region is proposed as the appropriate rim cavity pressure that is instrumental, along with the main annulus pressure, in driving ingestion and egress.

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received January 14, 2015; final manuscript received March 11, 2015; published online April 15, 2015. Editor: Ronald Bunker.

J. Turbomach 137(9), 091010 (Sep 01, 2015) (10 pages) Paper No: TURBO-15-1012; doi: 10.1115/1.4030099 History: Received January 14, 2015; Revised March 11, 2015; Online April 15, 2015

This paper describes experiments in a subscale axial turbine stage equipped with an axially overlapping radial-clearance seal at the disk cavity rim and a labyrinth seal radially inboard which divides the disk cavity into a rim cavity and an inner cavity. An orifice model of the rim seal is presented; values of ingestion and egress discharge coefficients based on the model and experimental data are reported for a range of cavity purge flow rate. In the experiments, time-averaged pressure distribution was measured in the main gas annulus and in the disk cavity; also measured was the time-averaged ingestion into the cavity. The pressure and ingestion data were combined to obtain the discharge coefficients. Locations on the vane platform 1 mm upstream of its lip over two vane pitches circumferentially defined the main gas annulus pressure; in the rim cavity, locations at the stator surface in the radially inner part of the “seal region” over one vane pitch defined the cavity pressure. For the sealing effectiveness, two locations in the rim cavity at the stator surface, one in the “mixing region” and the other radially further inward at the beginning of the stator boundary layer were considered. Two corresponding sets of ingestion and egress discharge coefficients are reported. The ingestion discharge coefficient was found to decrease in magnitude as the purge flow rate increased; the egress discharge coefficient increased with purge flow rate. The discharge coefficients embody fluid-mechanical effects in the ingestion and egress flows. Additionally, the minimum purge flow rate required to prevent ingestion was estimated for each experiment set and is reported. It is suggested that the experiments were in the combined ingestion (CI) region with externally induced (EI) ingestion being the dominant contributor.

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References

Figures

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Fig. 1

Schematic diagram of the single-stage turbine (C: concentration tap on stator surface, C: traverse concentration tap, P: pressure tap, and T: thermocouple)

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Fig. 2

Circumferential locations of static pressure taps on vane platform in main gas flow annulus at 1 mm downstream of vane trailing edge plane and 1 mm upstream of vane platform lip

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Fig. 3

Circumferential distribution of static pressure at main gas annulus outer shroud over two vane pitches at three axial positions for one experiment set I condition (cw = 1538)

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Fig. 4

Circumferential distribution of static pressure at vane platform and in rim cavity at stator surface for one experiment set I condition (cw = 1538)

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Fig. 5

Radial distributions of static pressure in rim and inner cavities at stator surface—experiment set I conditions; the inset shows distributions of rim cavity pressure, each distribution offset along the ordinate by a constant value for clarity

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Fig. 6

Radial distributions of local sealing effectiveness in rim and inner cavities at stator surface—experiment set I conditions

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Fig. 7

Radial distributions of local sealing effectiveness in rim and inner cavities at stator surface—experiment set II conditions

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Fig. 8

Sealing effectiveness at (a) r = 179 mm and (b) r = 173 mm on stator surface versus cw; and sealing effectiveness at (c) r = 173 mm, 179 mm, and 187 mm (r/Rh = 0.884, 0.915, and 0.956, respectively) on stator surface versus cw/2πGcReϕ. Also shown are three best-fit lines for the data.

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Fig. 9

Variation of cw,ing with cw for experiment set I (a) and set II (b) based on sealing effectiveness at r = 173 mm and 179 mm. cw,ing values at zero purge flow (encircled) were obtained by extrapolation of best-fit lines to cw = 0.

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Fig. 10

Ingestion and egress regions in one vane pitch (a) a schematic and (b) for two actual experiments—experiment set I

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Fig. 11

Discharge coefficients versus cw, based on sealing effectiveness at (a) r = 179 mm and (b) r = 173 mm

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Fig. 12

Discharge coefficients versus Vrim seal/Vax, based on sealing effectiveness at (a) r = 179 mm and (b) r = 173 mm

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