Research Papers

Implicit Large Eddy Simulation of a Stalled Low-Pressure Turbine Airfoil

[+] Author and Article Information
C. L. Memory

Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: Curtis.Memory@pw.utc.com

J. P. Chen, J. P. Bons

Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received December 5, 2015; final manuscript received December 21, 2015; published online February 17, 2016. Editor: Kenneth C. Hall.

J. Turbomach 138(7), 071008 (Feb 17, 2016) (10 pages) Paper No: TURBO-15-1294; doi: 10.1115/1.4032365 History: Received December 05, 2015; Revised December 21, 2015

Time-accurate numerical simulations were conducted on the aft-loaded L1A low-pressure turbine airfoil at a Reynolds number of 22,000 (based on inlet velocity magnitude and axial chord length). This flow condition produces a nonreattaching laminar separation zone on the airfoil suction surface. The numerical code TURBO is used to simulate this flow field as an implicit large eddy simulation (ILES). Generally, good agreement was found when compared to experimental time-averaged and instantaneous flow measurements. The numerical separation zone is slightly larger than that in the experiments, though integrated wake loss values improved from Reynolds-averaged Navier–Stokes (RANS)-based simulations. Instantaneous snapshots of the numerical flow field showed the Kelvin Helmholtz instability forming in the separated shear layer and a large-scale vortex shedding pattern at the airfoil trailing edge. These features were observed in the experiments with similar sizes and vorticity levels. Power spectral density analyses revealed a global passage oscillation in the numerics that was not observed experimentally. This oscillation was most likely a primary resonant frequency of the numerical domain.

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Fig. 1

Schematic of linear cascade wind tunnel. Note rotated coordinate system used in PIV data windows.

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Fig. 2

Numerical domain and associated boundary conditions. Numerical grid is shown for region near the point of flow separation (left) and in the separated wake (right).

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Fig. 3

Pressure coefficient distributions for various numerical grids versus experimental data at Re = 22,000 and 60,000

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Fig. 7

Wall-normal profiles of instantaneous wall-tangent velocity and scaled vorticity magnitude, ωmagCax/Uin, from the ILES at various axial chord locations located within the laminar separated shear layer region. Solid lines are at minimum wall-normal distance, and dashed lines are at maximum wall-normal distance.

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Fig. 4

Integrated wake loss as a function of inlet Reynolds number. Inset streamline plots show time-averaged numerical flow fields from Re = 22,000 and 90,000 cases at blade trailing edge region. △ Kiel measurement, □ ILES, and ◯ numerical predictions cited in Bons et al. [18].

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Fig. 5

Contours of instantaneous numerical vorticity magnitude, ωmagCax/Uin at Re = 22,000. Black rectangular outlines represent the regions of PIV data measurements. Dashed wall-normal lines are hot-film measurement locations.

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Fig. 6

Wall-normal profiles of time-averaged velocity magnitude from ILES simulations

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Fig. 8

Contours from numerics of instantaneous spanwise vorticity, ωzCax/Uin, with streamlines. Top plot is vortex pattern created when shear layer is in transition away from the airfoil wall, and bottom plot is vortex pattern representative of all other shear layer oscillation positions.

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Fig. 9

Contours from various PIV snapshots of instantaneous spanwise vorticity, ωzCax/Uin, with streamlines showing shear layer decay vortices. Shear layer wall-normal positions do not coincide with Fig. 8.

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Fig. 10

Contours and wall-normal profiles of time-averaged velocity magnitude from PIV (black squares in line plots), hot film (gray squares in line plots), and ILES (solid line in line plots)

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Fig. 13

Comparison of time-averaged PIV and numerical velocity components in the s–n plane. Dashed diagonal lines indicate distance from airfoil trailing edge in x–y coordinate plane normalized by Cax.

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Fig. 11

Contours and wall-normal profiles of time-averaged velocity magnitude RMS from PIV (black squares in line plots), hot film (gray squares in line plots), and ILES (solid line in line plots)

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Fig. 12

Contours of instantaneous spanwise vorticity from PIV and ILES showing trailing edge vortex formation. Vortex rotation sense is counterclockwise on the page.

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Fig. 14

Numerical power spectral density (right) of velocity magnitude oscillating component, obtained from maximum RMS location in wall-normal profiles at various Cax locations. Signal sample windows are also shown (left).

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Fig. 15

Experimental power spectral density of velocity magnitude obtained from maximum skewness location in wall-normal profile at 70% Cax

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Fig. 16

Numerical power spectral density of static pressure located at midpassage and 50% Cax



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