Research Papers: Gas Turbines: Turbomachinery

A Sensitivity Study of Gas Turbine Exhaust Diffuser-Collector Performance at Various Inlet Swirl Angles and Strut Stagger Angles

[+] Author and Article Information
Michal P. Siorek

Turbine Aerodynamics,
Solar Turbines Incorporated,
San Diego, CA 92186
e-mail: Siorek_Michal_P@solarturbines.com

Stephen Guillot

President of Engineering,
Techsburg Inc.,
265 Industrial Drive,
Christiansburg, VA 24073
e-mail: sguillot@techsburg.com

Song Xue

Techsburg Inc.,
265 Industrial Drive,
Christiansburg, VA 24073

Wing F. Ng

CEO and Chairman
Techsburg Inc.,
265 Industrial Drive,
Christiansburg, VA 24073
e-mail: wng@techsburg.com

1Present address: Concepts NREC, 217 Billings Farm Road, White River Junction, VT 05001.

2Present address: Chris C. Kraft Endowed Professor, Department of Mechanical Engineering, Virginia Tech, 425 Goodwin Hall - 0238, 635 Prices Fork Road, Blacksburg, VA 24061.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 28, 2017; final manuscript received December 11, 2017; published online April 20, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(7), 072602 (Apr 20, 2018) (14 pages) Paper No: GTP-17-1411; doi: 10.1115/1.4038856 History: Received July 28, 2017; Revised December 11, 2017

This paper describes studies completed using a quarter-scaled rig to assess the impact of turbine exit swirl angle and strut stagger on a turbine exhaust system consisting of an integral diffuser-collector. Advanced testing methods were applied to ascertain exhaust performance for a range of inlet conditions aerodynamically matched to flow exiting an industrial gas turbine. Flow visualization techniques along with complementary computational fluid dynamics (CFD) predictions were used to study flow behavior along the diffuser end walls. Complimentary CFD analysis was also completed with the aim to ascertain the performance prediction capability of modern day analytical tools for design phase and off-design analysis. The K-Epsilon model adequately captured the relevant flow features within both the diffuser and collector, and the model accurately predicted the recovery at design conditions. At off-design conditions, the recovery predictions were found to be pessimistic. The integral diffuser-collector exhaust accommodated a significant amount of inlet swirl without degradation in performance, so long as the inlet flow direction did not significantly deviate from the strut stagger angle. Strut incidence at the hub was directly correlated with reduction in overall performance, whereas the diffuser-collector performance was not significantly impacted by strut incidence at the shroud.

Copyright © 2018 by ASME
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Fig. 1

Subsonic wind tunnel facility for the testing of 1/4 scale diffuser collector

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Fig. 2

The diffuser-collector test rig hardware

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Fig. 3

Section view of the diffuser-collector rig

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Fig. 4

Diffuser strut profiles and stagger angles

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Fig. 5

Forward looking aft view of the exhaust diffuser showing strut lean

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Fig. 6

Location of the diffuser endwall and collector exit pressure taps

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Fig. 7

Locations of PIV measurement planes

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Fig. 8

Radial distribution of the inlet total pressure coefficient, Cpo—circumferentially averaged

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Fig. 9

Radial distribution of the inlet Mach number, circumferentially averaged

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Fig. 10

Exhaust diffuser-collector recovery change as a function of inlet swirl and strut stagger angle (top), compared along the radial distribution of inlet swirl angle (bottom): (a) strut stagger angle +12 deg, (b) strut stagger angle −12 deg, and (c) strut stagger angle 0 deg

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Fig. 11

Computational fluid dynamics prediction of Cp relative to experimental data, evaluated for various turbulence models, swirl 6.6 deg, axial strut

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Fig. 12

Computational fluid dynamics prediction capability of endwall static pressure recovery for select turbulence models

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Fig. 13

Computational fluid dynamics predictions of the Mach number through the exhaust diffuser-collector cross section (a) K-Epsilon two-layer, (b) SST, (c) DES–EB, and (d) DES–SST

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Fig. 14

Particle image velocimetry measurements and CFD predictions of collector exit normal velocity component normalized to inlet velocity: (a) PIV measurements, (b) CFD prediction—SST (Menter) model, (c) CFD prediction—k–Epsilon two-layer model, (d) CFD prediction—K–Epsilon EB model, (e) CFD prediction—RSM model—LPS, (f) CFD prediction—RSM model—quad. pressure strain, (g) CFD prediction—DES-EB model—ensemble average, and (h) CFD prediction—DES-SST model—ensemble average.

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Fig. 15

Impact of incidence at the (a) hub and (b) shroud on exhaust diffuser-collector recovery

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Fig. 16

Pressure recovery along the hub (a) TDC and (b) BDC

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Fig. 17

Pressure recovery along the shroud (a) TDC and (b) BDC

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Fig. 18

Surface flow visualization along the diffuser hub BDC location: (a) hub incidence +2 deg, shroud incidence +10 deg; (b) hub incidence −22 deg, shroud incidence −14 deg

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Fig. 19

Surface flow visualization along the diffuser shroud BDC location: (a) Hub incidence 2 deg, shroud incidence 10 deg; (b) Hub incidence −22 deg, shroud incidence −14 deg

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Fig. 20

Streamlines predicted with CFD along the diffuser-collector hub: (a) Hub incidence +2 deg, shroud incidence +10 deg; (b) Hub incidence −22 deg, shroud incidence −14 deg; (c) Hub incidence −35 deg, shroud incidence −19 deg; (d) Hub incidence +15 deg, shroud incidence +34 deg

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Fig. 21

Streamlines predicted with CFD along the diffuser-collector shroud: (a) Hub incidence +2 deg, shroud incidence +10 deg; (b) Hub incidence −22 deg, shroud incidence −14 deg; (c) Hub incidence −35 deg, shroud incidence −19 deg; (d) Hub incidence +15 deg, shroud incidence +34 deg



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