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Research Papers

Investigation of Unsteady Flow Phenomena in First Vane Caused by Combustor Flow With Swirl

[+] Author and Article Information
Simon Jacobi

Osney Thermo-Fluids Laboratory,
Department of Engineering Science,
University of Oxford,
Oxford OX2 0ES, UK
e-mail: simon.jacobi@eng.ox.ac.uk

Cosimo Mazzoni, Budimir Rosic

Osney Thermo-Fluids Laboratory,
Department of Engineering Science,
University of Oxford,
Oxford OX2 0ES, UK

Krishan Chana

Whittle Laboratory,
Department of Engineering,
Cambridge University,
Cambridge CB3 0DY, UK

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 22, 2016; final manuscript received October 22, 2016; published online January 10, 2017. Editor: Kenneth Hall.

J. Turbomach 139(4), 041006 (Jan 10, 2017) (12 pages) Paper No: TURBO-16-1167; doi: 10.1115/1.4035073 History: Received July 22, 2016; Revised October 22, 2016

The flow at the combustor turbine interface of power generation gas turbines with can combustors is characterized by high and nonuniform turbulence levels, lengthscales, and residual swirl. These complexities have a significant impact on the first vanes aerothermal performance and lead to challenges for an effective turbine design. To date, this design philosophy mostly assumed steady flow and thus largely disregards the intrinsic unsteadiness. This paper investigates the steady and unsteady effects of the combustor flow with swirl on the turbines first vanes. Experimental measurements are conducted on a high-speed linear cascade that comprises two can combustors and four nozzle guide vanes (NGVs). The experimental results are supported by a large eddy simulation (LES) performed with the inhouse computational fluid dynamics (CFD) flow solver TBLOCK. The study reveals the highly unsteady nature of the flow in the first vane and its effect on the heat transfer. A persistent flow structure of concentrated vorticity is observed. It wraps around the unshielded vane's leading edge (LE) at midspan and periodically oscillates in spanwise direction due to the interaction of the residual low-pressure swirl core and the vane's potential field. Moreover, the transient behavior of the horseshoe-vortex system due to large fluctuations in incidence is demonstrated.

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References

Figures

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Fig. 1

Schematic of unsteady interaction between residual swirl core and vane's potential field, and of unsteady nature of passage vortex

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Fig. 2

CAD (top) and photo (bottom) of the experimental facility's working section (view from downstream), including swirlers, transition ducts, and nozzle guide vanes

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Fig. 3

Schematic of computational domain for steady CFD and LES; horizontal cut at midspan illustrating structured mesh for LES of swirler and vane passages

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Fig. 4

Isosurface of total pressure obtained from instantaneous time step of LES

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Fig. 5

Energy cascade of LES for two midspan points in the computational domain

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Fig. 6

Turbulence intensity within transition duct and vane passages at midspan (time-averaged LES)

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Fig. 7

Dimensionless total pressure (top), yaw (middle), and pitch (bottom) distributions downstream of the transition duct; obtained through traverse measurements with installed swirler

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Fig. 8

Dimensionless total pressure (top) and yaw (bottom) distributions downstream of the nozzle guide vanes; obtained through traverse measurements with installed swirler

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Fig. 9

Pitchwise averaged dimensionless total pressure (left) and yaw (right) downstream of the nozzle guide vanes for experimental measurements (dashed) and time-averaged LES (solid) with swirler

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Fig. 10

Schematic of interaction between residual swirl core and vane potential field (a) total pressure loss core in presence of vane potential field, (b) swirl, and (c) swirl reversed

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Fig. 11

Static pressure contour and stagnation line at unshielded vane's leading edge for a no-swirl (top), swirl (middle), and reversed swirl (bottom) case; based on steady CFD (a) no swirl, (b) swirl, and (c) swirl rev

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Fig. 12

Dimensionless total pressure distribution at vanes trailing edges for swirl (top) and reversed swirl (bottom) scenario; streamtraces of residual swirl core and endwall boundary layer; steady CFD (a) swirl and (b) swirl reversed

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Fig. 13

Heat transfer coefficient distributions on the vanes suction surfaces obtained from experimental measurements (top) and steady CFD simulations (bottom) for a swirl (left) and reversed swirl (right) case (a) swirl and (b) swirl reversed

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Fig. 14

Wall shear stress on unshielded vane's suction surface for three time steps with isosurface of lambda 2 criterion (top); graph of wall shear stress for a point on the leading edge over time (bottom)

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Fig. 15

Discrete Fourier transformation of unshielded vane's temperature obtained from experimental thin-film gauge measurements on the pressure side (left), leading edge (middle) and suction side (right) for a no-swirl (top), swirl (middle), and reversed swirl (bottom) scenario

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Fig. 16

Discrete Fourier transformation of unshielded vane's heat flux obtained from LES for point on the pressure side (left), leading edge (middle), and suction side (right) for the swirl scenario

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Fig. 17

Isosurface of lambda 2 criterion in vane passages

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Fig. 18

Unsteadiness of upstream pitchwise-averaged yaw

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Fig. 19

Isosurface of lambda 2 criterion in vane passages; looking from downstream

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