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Research Papers

Effects of Density and Blowing Ratios on the Turbulent Structure and Effectiveness of Film Cooling

[+] Author and Article Information
Zachary T. Stratton

School of Aeronautics and Astronautics,
Purdue University,
West Lafayette, IN 47907
e-mail: zstratto@purdue.edu

Tom I-P. Shih

School of Aeronautics and Astronautics,
Purdue University,
West Lafayette, IN 47907

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 9, 2018; final manuscript received August 16, 2018; published online September 28, 2018. Editor: Kenneth Hall.

J. Turbomach 140(10), 101007 (Sep 28, 2018) (12 pages) Paper No: TURBO-18-1195; doi: 10.1115/1.4041218 History: Received August 09, 2018; Revised August 16, 2018

Large eddy simulations (LES) were performed to investigate film cooling of a flat plate, where the cooling jets issued from a plenum through one row of circular holes of diameter D and length 4.7D that are inclined at 35 deg relative to the plate. The focus is on understanding the turbulent structure of the film-cooling jet and the film-cooling effectiveness. Parameters studied include blowing ratio (BR = 0.5 and 1.0) and density ratio (DR = 1.1 and 1.6). Also, two different boundary layers (BL) upstream of the film-cooling hole were investigated—one in which a laminar BL was tripped to become turbulent from near the leading edge of the flat plate, and another in which a mean turbulent BL is prescribed directly. The wall-resolved LES solutions generated were validated by comparing its time-averaged values with data from PIV and thermal measurements. Results obtained show that having an upstream BL that does not have turbulent fluctuations enhances the cooling effectiveness significantly at low velocity ratios (VR) when compared to an upstream BL that resolved the turbulent fluctuations. However, these differences diminish at higher VRs. Instantaneous flow reveals a bifurcation in the jet vorticity as it exits the hole at low VRs, one branch forming the shear-layer vortex, while the other forms the counter-rotating vortex pair (CRVP). At higher VRs, the shear layer vorticity is found to reverse direction, changing the nature of the turbulence and the heat transfer. Results obtained also show the strength and structure of the turbulence in the film-cooling jet to be strongly correlated to VR.

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Figures

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Fig. 1

Computational model

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Fig. 2

Computational mesh. Top: centerline slice. Bottom: hole exit slice at the wall (hole edge is highlighted).

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Fig. 6

Velocity measurements along centerline

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Fig. 7

Q-Criterion colored by θ with 2D contour of ωz: (a) case 1 (VR = 0.31 (low BR/high DR)), (b) case 2 (VR = 0.46 (low BR/low DR)), (c) case 3 (VR = 0.63 (high BR/high DR)), and (d) case 4 (VR = 0.91 (high BR/low DR))

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Fig. 8

Sketch of flow structure near the hole: (a) low VR and (b) high VR

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Fig. 3

Turbulent BL profile nondimensionalized by viscous units at Reδmom = 670

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Fig. 4

Turbulent x-velocity fluctuation nondimensionalized by viscous units at Reδmom = 670

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Fig. 5

Adiabatic effectiveness measurements

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Fig. 9

Instantaneous nondimensional temperature at Y/D = 0.05: (a) case 1 (VR = 0.31 (low BR/high DR)), (b) case 2 (VR = 0.46 (low BR/low DR)), (c) case 3 (VR = 0.63 (high BR/high DR)), and (d) case 4 (VR = 0.91 (high BR/low DR))

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Fig. 10

Time-averaged non-dimensional temperature with ωx contour lines at X/D = 0.5 and 2: (a) case 1 (VR = 0.31 (low BR/high DR)), (b) case 2 (VR = 0.46 (low BR/low DR)), (c) case 3 (VR = 0.63 (high BR/high DR)), and (d) case 4 (VR = 0.91 (high BR/low DR))

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Fig. 11

Favre-averaged nondimensional Reynolds normal stresses at X/D = 2: a) case 1 (VR = 0.31 (low BR/high DR)), (b) case 2 (VR = 0.46 (low BR/low DR)), (c) case 3 (VR = 0.63 (high BR/high DR)), and (d) case 4 (VR = 0.91 (high BR/low DR))

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Fig. 12

Favre-averaged nondimensional Reynolds shear stresses at X/D = 2: (a) case 1 VR = 0.31 (low BR/high DR), (b) case 2 VR = 0.46 (low BR/low DR), (c) case 3 VR = 0.63 (high BR/high DR), and (d) case 4 VR = 0.31 (high BR/low DR)

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Fig. 13

Favre-averaged nondimensional turbulent heat fluxes at X/D = 2: (a) case 1 (VR = 0.31 (low BR/high DR)); (b) case 2 (VR = 0.46 (low BR/low DR)), (c) case 3 (VR = 0.63 (high BR/high DR)), and (d) case 4 (VR = 0.91 (high BR/low DR))

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Fig. 14

Time-averaged non-dimensional temperature with ωx contour lines at X/D = 2 for a mean and turbulent BL: (a) cases 1 and 5 (low VR) and (b) cases 4 and 8 (high VR)

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Fig. 15

Nondimensional turbulent kinetic energy at X/D = 2: (a) case 1 and case 5 (low VR) and (b) case 4 and case 8 (high VR)

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