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Research Papers

Comparison of RANS and Detached Eddy Simulation Modeling Against Measurements of Leading Edge Film Cooling on a First-Stage Vane

[+] Author and Article Information
S. Ravelli

Department of Engineering and
Applied Sciences,
University of Bergamo,
Marconi Street 5,
Dalmine, BG 24044, Italy
e-mail: silvia.ravelli@unibg.it

G. Barigozzi

Department of Engineering and
Applied Sciences,
University of Bergamo,
Marconi Street 5,
Dalmine, BG 24044, Italy
e-mail: giovanna.barigozzi@unibg.it

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 2, 2016; final manuscript received September 22, 2016; published online January 24, 2017. Editor: Kenneth Hall.

J. Turbomach 139(5), 051005 (Jan 24, 2017) (12 pages) Paper No: TURBO-16-1180; doi: 10.1115/1.4035161 History: Received August 02, 2016; Revised September 22, 2016

The performance of a showerhead arrangement of film cooling in the leading edge region of a first-stage nozzle guide vane was experimentally and numerically evaluated. A six-vane linear cascade was tested at an isentropic exit Mach number of Ma2s = 0.42, with a high inlet turbulence intensity level of 9%. The showerhead cooling scheme consists of four staggered rows of cylindrical holes evenly distributed around the stagnation line, angled at 45 deg toward the tip. The blowing ratios tested are BR = 2.0, 3.0, and 4.0. Adiabatic film cooling effectiveness distributions on the vane surface around the leading edge region were measured by means of thermochromic liquid crystals (TLC) technique. Since the experimental contours of adiabatic effectiveness showed that there is no periodicity across the span, the computational fluid dynamics (CFD) calculations were conducted by simulating the whole vane. Within the Reynolds-averaged Navier–Stokes (RANS) framework, the very widely used realizable k–ε (Rke) and the shear stress transport k–ω (SST) turbulence models were chosen for simulating the effect of the BR on the surface distribution of adiabatic effectiveness. The turbulence model which provided the most accurate steady prediction, i.e., Rke, was selected for running detached eddy simulation (DES) at the intermediate value of BR = 3. Fluctuations of the local temperature were computed by DES, due to the vortex structures within the shear layers between the main flow and the coolant jets. Moreover, mixing was enhanced both in the wall-normal and spanwise directions, compared to RANS modeling. DES roughly halved the prediction error of laterally averaged film cooling effectiveness on the suction side of the leading edge. However, neither DES nor RANS provided the expected decay of effectiveness progressing downstream along the pressure side, with 15% overestimation of ηav at s/C = 0.2.

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References

Figures

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Fig. 2

Cascade model and cooling scheme

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Fig. 3

Inlet boundary layer (X/cax = −1.6)

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Fig. 4

TLC measurement setup

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Fig. 6

Conduction correction at time t = 25 s

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Fig. 7

Three-dimensional computational domain and boundary conditions

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Fig. 8

Cross-sectional view of the mesh in the leading edge region with monitor points

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Fig. 9

Zoomed-in view of plenum and cooling holes surface mesh

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Fig. 10

Grid resolution test at BR values of 2.0 and 3.0: SST–RANS predictions of laterally averaged adiabatic effectiveness

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Fig. 11

Mais distributions for the solid (Exp) and the cooled (Num) vane, at BR = 3.0

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Fig. 12

Contours of adiabatic effectiveness η from experimental measurements (left), SST (middle), and Rke (right) predictions for (a)–(c) BR = 2.0, (d)–(f) BR = 3.0, and (g)–(i) BR = 4.0

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Fig. 13

Pathlines originated from the cooling holes as a function of the normalized temperature θ at BR = 2.0 for (a) SST and (b) Rke models

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Fig. 14

Pathlines originated from the cooling holes as a function of the normalized temperature θ at BR = 4.0 for the Rke model

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Fig. 15

Measurements (Exp) versus SST and Rke predictions of laterally averaged adiabatic effectiveness ηav at (a) BR = 2.0, (b) BR = 3.0, and (c) BR = 4.0, within 0.025 < Z/H < 0.7

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Fig. 16

Instantaneous pathlines originated from the cooling holes as a function of cell wall distance (m) at BR = 3.0, for the DES model

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Fig. 17

Predictions of (a) outlet coolant flow rate and (b) discharge coefficient CD for the showerhead holes, at BR = 3

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Fig. 18

DES isosurface of Q = 2 × 109 s−2 as a function of the normalized temperature θ at BR = 3.0 (top view of the showerhead)

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Fig. 19

Time-averaged DES contours of adiabatic effectiveness η at BR = 3.0

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Fig. 20

Measurements (Exp) versus DES and RANS (Rke) predictions of laterally averaged adiabatic effectiveness ηav at BR = 3.0, within 0.025 < Z/H < 0.7

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