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Research Papers: Forced Convection

Numerical Investigation on Diffusion Slot Hole With Various Cross-Sectional End Shapes

[+] Author and Article Information
Bai-Tao An

Institute of Engineering Thermophysics,
Chinese Academy of Sciences,
Beijing 100190, China
e-mail: anbt@mail.etp.ac.cn

Jian-Jun Liu

Institute of Engineering Thermophysics,
Chinese Academy of Sciences,
Beijing 100190, China

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received July 14, 2016; final manuscript received March 24, 2017; published online May 9, 2017. Assoc. Editor: Jim A. Liburdy.

J. Heat Transfer 139(9), 091703 (May 09, 2017) (13 pages) Paper No: HT-16-1463; doi: 10.1115/1.4036523 History: Received July 14, 2016; Revised March 24, 2017

The diffusion hole constructed on a slot-type cross section has the potential to obtain high film cooling performance. However, the end shape of the cross section can greatly affect film cooling characteristics. This study examined eight cases of diffusion slot holes with various cross-sectional end shapes. The comparison of the eight diffusion slot holes and a typical fan-shaped hole was performed with a flat plate model using a three-dimensional (3D) steady computational fluid dynamics (CFD) method. The rectangular cross section had an aspect ratio of about 3.4. The end shape variation can be described based on sidewall contraction location, size, and form. The simulations were performed under an engine-representative condition of mainstream inlet Mach number 0.3 and turbulence intensity 5.2%. The simulated results showed that a strip separation bubble caused by inlet “jetting effect” occurs near the downstream wall of the diffusion slot hole and interacts with the diffusion flow. The different end shape of the rectangular cross section leads to different sidewall static pressure and exit velocity profiles, thereby produces three cooling effectiveness patterns, single-peak, bipeak, and tripeak patterns. The tripeak pattern produces higher cooling effectiveness and relatively uniform film coverage. The structure with moderate contraction and smooth transition on two sides of the downstream wall favors creation of a tripeak pattern. Compared with the fan-shaped hole, the discharge coefficient of diffusion slot hole is slightly small in low pressure ratio range, the pressure loss ratio has little difference.

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Figures

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Fig. 1

Typical configurations of fan-shaped hole [14]

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Fig. 2

Typical configurations of diffusion slot hole

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Fig. 3

End shape cases of rectangular cross section of the diffusion slot hole (A–A plane in Fig. 2)

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Fig. 4

Computation domain model: (a) 3D view and (b) side and top view

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Fig. 5

Laterally averaged effectiveness of fan-shaped hole at M = 1.5 obtained by previous experimental and present numerical simulations

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Fig. 6

Absolute velocity contours predicted by three turbulence models on hole centerline plane: (a) standard k–ε, (b) SST k–ω, and (c) RNG k–ε

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Fig. 7

Grid independency test on laterally averaged cooling effectiveness of fan-shaped hole at M = 1.5

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Fig. 8

Adiabatic cooling effectiveness contours of fan-shaped hole at various blowing ratios

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Fig. 9

Adiabatic cooling effectiveness contours of eight diffusion slot holes at various blowing ratios: (a) case 1, (b) case 2, (c) case 3, (d) case 4, (e) case 5, (f) case 6, (g) case 7, and (h) case 8

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Fig. 10

Comparison of lateral cooling effectiveness distribution on x/D = 10 at three simulated blowing ratios: (a) M = 0.5, (b) M = 1.5, and (c) M = 2.5

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Fig. 11

Comparison of laterally averaged cooling effectiveness at three simulated blowing ratios: (a) M = 0.5, (b) M = 1.5, and (c) M = 2.5

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Fig. 12

Comparison of spatially averaged cooling effectiveness of all simulated holes at three different blowing ratios

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Fig. 13

Comparison of velocity contours and velocity vector streamline on hole centerline plane at blowing ratio M = 1.5: (a) fan-shaped hole and (b) diffusion slot hole case 2

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Fig. 14

Positions of cutting planes on Z-direction and hole flow direction

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Fig. 15

Absolute velocity contours on three Z-direction planes inside the fan-shaped hole at three different blowing ratios: (a) M = 0.5, (b) M = 1.5, and (c) M = 2.5

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Fig. 16

Absolute velocity contours on five Z-direction planes inside the diffusion slot hole at M = 1.5: (a) case 1, (b) case 2, (c) case 3, (d) case 4, (e) case 5, (f) case 6, (g) case 7, and (h) case 8

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Fig. 17

Static pressure contours on cutting plane 6 at M = 1.5 (viewing from the A direction in Fig. 14): (a) case 1, (b) case 2, (c) case 3, (d) case 4, (e) case 5, (f) case 6, (g) case 7, and (h) case 8

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Fig. 18

Velocity vector streamline distribution on downstream x/D = 5 plane of fan-shaped hole (left: M = 0.5, middle: M = 1.5, and right: M = 2.5)

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Fig. 19

Velocity vector streamline distribution on downstream x/D = 5 plane of four typical diffusion slot holes (left: M = 0.5, middle: M = 1.5, and right: M = 2.5): (a) case 1, (b) case 3, (c) case 5, and (d) case 7

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Fig. 20

Discharge coefficients variation along with pressure ratios for all simulated hole geometries

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Fig. 21

Pressure loss ratio variation along with blowing ratios for all simulated hole geometries

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