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Research Papers: Flows in Complex Systems

Factors Influencing Computational Predictability of Aerodynamic Losses in a Turbine Nozzle Guide Vane Flow

[+] Author and Article Information
Özhan H. Turgut

Department of Aerospace Engineering,
The Pennsylvania State University,
University Park, PA 16802
e-mail: Ozhan_Turgut@gmail.com

Cengiz Camci

Professor
Fellow ASME
Department of Aerospace Engineering,
The Pennsylvania State University,
223 Hammond Building,
University Park, PA 16802
e-mail: cxc11@psu.edu

1Present address: Turbomachinery Aerodynamics, Praxair, Inc., 175 East Park Drive, Tonawanda, NY 14150.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 17, 2015; final manuscript received September 28, 2015; published online January 5, 2016. Assoc. Editor: Frank C. Visser.

J. Fluids Eng 138(5), 051103 (Jan 05, 2016) (13 pages) Paper No: FE-15-1265; doi: 10.1115/1.4031879 History: Received April 17, 2015; Revised September 28, 2015

This paper deals with the computational predictability of aerodynamic losses in a turbine nozzle guide vane (NGV) flow. The paper shows that three-dimensional (3D) computations of Reynolds-Averaged Navier Stokes (RANS) equations have the ability to adequately represent viscous losses in the presence of laminar flows, transitional regions, and fully turbulent flow areas in the NGV of an high pressure (HP) turbine stage. The Axial Flow Turbine Research Facility (AFTRF) used for the present experimental results has an annular NGV assembly and a 29-bladed HP turbine rotor spinning at 1330 rpm. The NGV inlet and exit Reynolds numbers based on midspan axial chord are around 300,000 and 900,000, respectively. A general purpose finite-volume 3D flow solver with a shear stress transport (SST) k–ω turbulence model is employed. The current computational study benefits from these carefully executed aerodynamic experiments in the NGV of the AFTRF. The grid independence study is performed with static pressure coefficient distribution at the midspan of the vane and the total pressure coefficient at the NGV exit. The effect of grid structure on aerodynamic loss generation is emphasized. The flow transition effect and the influence of corner fillets at the vane–endwall junction are also studied. The velocity distributions and the total pressure coefficient at the NGV exit plane are in very good agreement with the experimental data. This validation study shows that the effect of future geometrical modifications on the turbine endwall surfaces will be predicted reasonably accurately. The current study also indicates that an accurately defined turbine stage geometry, a properly prepared block-structured/body-fitted grid, a state-of-the-art transitional flow implementation, inclusion of fillets, and realistic boundary conditions coming from high-resolution turbine experiments are all essential ingredients of a successful turbine NGV aerodynamic loss quantification via computations. This validation study forms the basis for the successful future generation of nonaxisymmetric endwall surface modifications in AFTRF research efforts.

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Figures

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Fig. 1

The rotating, large-scale turbine facility sketch, AFTRF

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Fig. 2

Experimental inlet velocity magnitude and turbulent kinetic energy distribution, measure one chord upstream of the AFTRF NGV assembly

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Fig. 6

Prediction of total pressure loss and comparison with AFTRF experimental data [11], unstructured mesh comparison at NGV exit plane: (a) 2.0 × 106 mesh cells, up to 20% span measured from the hub endwall, (b) 6.5 × 106 mesh cells, up to 20% span measured from the hub endwall, and (c) spanwise distribution of total pressure coefficient

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Fig. 5

Prediction of total pressure loss and comparison with AFTRF experimental data [11], effect of prism layer height on unstructured mesh at NGV exit plane: (a) 3.3 × 106 mesh cells with short prism layers, up to 20% span measured from the hub endwall, (b) 4.5 × 106 mesh cells with tall prism layers, up to 20% span measured from the hub endwall, and (c) spanwise distribution of total pressure coefficient

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Fig. 4

AFTRF, NGV exit plane definition

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Fig. 3

Unstructured grid, for the AFTRF NGV

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Fig. 10

Grid independence study on Cp at midspan with transition model, comparison with AFTRF experimental data [11]

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Fig. 9

Grid independence study on Cpt at NGV exit with transition model, comparison with AFTRF experimental data [11]

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Fig. 8

Grid independence study on Cpt at NGV exit without transition model, comparison with AFTRF experimental data [11]

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Fig. 11

Effect of corner fillet, comparison with AFTRF experimental data [11]

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Fig. 12

NGV exit plane total pressure coefficient contours: (a) AFTRF experiments [11], NGV exit plane measured CPt contours, x/c = 1.05 and (b) current computational result, NGV exit plane CPt contours, x/c = 1.05

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Fig. 13

Computed static pressure coefficient at NGV exit plane, comparison with AFTRF experimental data [11]

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Fig. 14

Velocity components at NGV exit plane, comparison with AFTRF subminiature five-hole probe measurements [11]

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Fig. 15

Flow visualization in AFTRF NGV passage: (a) streamlines released from inlet, at 1% span, (b) streamlines released from inlet, at 50% span, (c) streamlines released from inlet, from hub to 5% span, leading edge view, and (d) streamlines released from inlet, from hub to 5% span, trailing edge view

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Fig. 16

Vortex cores visualized by the Q-criterion

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Fig. 7

Block-structured body-fitted mesh on AFTRF NGV surfaces

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Fig. 17

NGV five-section profile

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