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Research Papers

Effect of Vortex Generators on Film Cooling Effectiveness

[+] Author and Article Information
S. Sarkar

Professor
Mem. ASME
Department of Mechanical Engineering,
Indian Institute of Technology Kanpur,
Kanpur, Uttar Pradesh 208016, India
e-mail: subra@iitk.ac.in

Ganesh Ranakoti

Department of Mechanical Engineering,
Indian Institute of Technology Kanpur,
Kanpur, Uttar Pradesh 208016, India
e-mail: ganeshranakoti@yahoo.com

1Corresponding author.

2Present address: Department of Mechanical Engineering, Galgotias University, Greater Noida, Uttar Pradesh 201306, India.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 22, 2016; final manuscript received November 5, 2016; published online February 7, 2017. Editor: Kenneth Hall.

J. Turbomach 139(6), 061009 (Feb 07, 2017) (11 pages) Paper No: TURBO-16-1203; doi: 10.1115/1.4035275 History: Received August 22, 2016; Revised November 05, 2016

Film cooling is often adopted, where coolant jets are ejected to form a protective layer on the surface against the hot combustor gases. The bending of jets in crossflow results in counter rotating vortex pair (CRVP), which is a cause for high jet lift-off and poor film cooling effectiveness in the near field. There are efforts to mitigate this detrimental effect of CRVP, and thus, to improve the film cooling performance. In the present study, the effects of both downwash and upwash type of vortex generator (VG) on film cooling are numerically analyzed. A series of discrete holes on a flat plate with 35 deg streamwise orientation and connected to a common delivery plenum is used here, where the vortex generators are placed upstream of the holes. The blowing ratio and the density ratio are considered as 0.5 and 1.2, respectively, with a Reynolds number based on freestream velocity and diameter of hole being 15,885. The computations are performed by ANSYS fluent 13.0 using k–ε realizable turbulence model. The results show that vortices generated by downwash vortex generator (DWVG) counteracts the effect of CRVP preventing the jet lift-off, which results in increased effectiveness in streamwise as well as in spanwise directions. However, upwash vortex generator (UWVG) augments the effect of CRVP, resulting in poor performance of film cooling.

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References

Figures

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Fig. 4

Three dimensional solid model: (a) DWVG and (b) UWVG

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Fig. 3

Vortex generator placed upstream of film cooling hole: (a) DWVG and (b) UWVG

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Fig. 2

Schematic of (a) computation domain and (b) dimensions and imposed boundary conditions

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Fig. 1

Vortical structures in JICF [18]

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Fig. 5

Mesh used: (a) without vortex generator, (b) with DWVG, (c) UWVG, and (d) around film cooling hole

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Fig. 6

Distribution of streamwise film cooling effectiveness compared with experiment: (a) along the centerline and (b) span averaged

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Fig. 7

Velocity profiles are compared with LES [30] for blowing ratio, M = 0.5 at three streamwise locations, where X* is measured from center of film cooling hole

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Fig. 8

Evolution of streamwise vorticity upstream of holes: (a) DWVG and (b) UWVG

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Fig. 9

Streamlines at different streamwise locations illustrating the effect of vortex generator: (a) without VG, (b) DWVG, and (c) UWVG

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Fig. 10

Contours of velocity magnitude superimposed with streamlines at the midplane: (a) without VG, (b) DWVG, and (c) UWVG

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Fig. 11

Evolution of spanwise vorticity (ωz) contours at the midplane: (a) without VG, (b) DWVG, and (c) UWVG

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Fig. 12

Evolution of streamwise vorticity (ωx) contours at different streamwise locations: (a) without VG, (b) DWVG, and (c) UWVG

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Fig. 13

Evolution of wall normal vorticity (ωy) contours: (a) without VG, (b) DWVG, and (c) UWVG

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Fig. 14

Streamlines near the vortex generator: (a) DWVG and (b) UWVG

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Fig. 15

Nondimensional temperature distributions along the centreline of hole: (a) without VG, (b) DWVG, (c) UWVG, and (d) DWVG with lower height

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Fig. 16

Nondimensional temperature contours at streamwise locations: (a) without VG, (b) DWVG, (c) UWVG, and (d) DWVG with lower height

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Fig. 17

Nondimensional temperature contours superimposed with velocity vectors at streamwise locations (a) without VG, (b) DWVG, and (c) UWVG

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Fig. 18

Contours of adiabatic film cooling effectiveness: (a) without VG, (b) DWVG, (c) UWVG, and (d) DWVG with lower height

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Fig. 19

Distributions of adiabatic film cooling effectiveness along centerline of the hole with and without VG

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Fig. 20

Distributions of span-averaged film cooling effectiveness with and without VG

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Fig. 21

Overall loss with and without VG

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