Research Papers

Flow Field Investigations on the Effect of Rib Placement in a Cooling Channel With Film-Cooling

[+] Author and Article Information
Martin Kunze

e-mail: martin.kunze@tu-dresden.de

Konrad Vogeler

e-mail: konrad.vogeler@tu-dresden.de
Technische Universität Dresden,
Institute for Fluid Mechanics,
Dresden D-01062, Germany

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received April 19, 2013; final manuscript received April 23, 2013; published online September 26, 2013. Editor: David Wisler.

J. Turbomach 136(3), 031009 (Sep 26, 2013) (13 pages) Paper No: TURBO-13-1056; doi: 10.1115/1.4024691 History: Received April 19, 2013; Revised April 23, 2013

This paper presents experimental investigations on flat plate film-cooling in combination with a ribbed cooling channel. The effect of rib placement on the film-cooling injection and the flow in the cooling channel was studied. The velocity fields were measured using optical laser measurement techniques including LDA (laser doppler anemometry) and PIV (particle image velocimetry). A row of three cylindrical film holes is placed in the center rib segment of the cooling channel. The dimensionless rib-to-hole position s/D is varied from 4.5 to 10.5. The investigations are conducted at isothermal conditions for a variation of the coolant Reynolds number Rec,Dh from 10,000 up to 60,000 and for three blowing rates M = 0.5, 0.75, and 1.00. The flow field results for the film-cooling injection showed only a small influence of the rib placement. Due to different coolant-to-main flow pressure ratios across the row, a slight nonuniform share of coolant flow occurs. Intense streamwise mixing and decay of the turbulence in the film jet was observed within the first 10 hole diameters. Enhancement of the turbulence intensity inside the jet core was found with increasing coolant Reynolds numbers. Inside the internal cooling channel, the flow field showed significant influence of the rib position which is most pronounced at low Reynolds number (Rec,Dh = 10,000) and high blowing ratios (M = 1.0). The effect becomes significantly smaller when the Reynolds number is increased. This is mainly attributed to the strongly increasing channel mass flow which equals to a decreasing suction ratio SR = uh/uc of the holes. The experimental results are compared to comprehensive numerical simulations.

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Fig. 1

Schematic of the experimental rig arrangement. The position of the test section is highlighted.

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Fig. 2

Schematic of film-cooling hole (a) and rib geometry (b) used in the present experiments

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Fig. 3

Computational mesh of (a) fluid domain, (b) grid details for ribs, and (c) cooling holes

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Fig. 4

Comparison of normalized streamwise velocity plots u/um for the center hole (y/D = 0) and rib position s/D = 7.5, Rec,Dh = 10,000 between experimental results obtained by LDA and CFD prediction: (a) M = 0.50 and (b) M = 1.00

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Fig. 5

Comparison between CFD-prediction and LDA experimental data: velocity u/um and turbulence intensity profiles at centerline of the center hole (y/D = 0, x/D = 2) for two blowing rates M = 0.5, 1.0, Rec,Dh = 10,000 and center rib position s/D = 7.5; (a) M = 0.50 and (b) M = 1.00

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Fig. 6

Comparison of normalized lateral velocity plots u/um for streamwise position x/D = 2 and rib position s/D = 7.5, Rec,Dh = 10,000 between experimental results obtained by LDA and CFD prediction

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Fig. 7

Normalized velocity contours at x/D = 2 from LDA measurements for the variation of the coolant Reynolds number, center rib position s/D = 7.5 and M = 1.0

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Fig. 8

Jet turbulence intensity for the center hole (y/D = 0) from LDA measurements for the variation of the coolant Reynolds number Rec,Dh, center rib position s/D = 7.5, M = 1.0

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Fig. 9

Influence of the coolant Reynolds number on velocity u/um and turbulence intensity profiles at a constant blowing rate M = 1.0 and center rib position s/D = 7.5 (data obtained by LDA)

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Fig. 10

Influence of rib position s/D on time-averaged flow field from LDA measurements for x/D = 2, Rec,Dh = 10,000, M = 1.00

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Fig. 11

Streamwise vorticity ωx* in lateral direction at wall distance z/D = 0.25 for x/D = 2 and at z/D = 0.50 for x/D = 5 with variation of rib-to-hole position, Rec,Dh = 10,000 and M = 1.0

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Fig. 12

Velocity profiles at centerline of all three holes for two streamwise distances (x/D = 2, 5), M = 1.00, RecDh=10,000 with variation of rib-to-hole-distance s/D (obtained by LDA); (a) hole 1, y/D = −3; (b) hole 2, y/D = 0; and (c) hole 3, y/D = 3

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Fig. 13

CFD-predicted wall pressure ratio in the center rib segment with variation of the rib-to-hole position, M = 1.00, Rec,Dh = 10,000

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Fig. 14

Flow field in the cooling channel obtained by PIV with variation of coolant Reynolds number Rec,Dh, blowing rate M and rib-to-hole position s/D; (a) rib-to-hole position s/D = 4.5, (b) rib-to-hole position s/D = 7.5, and (c) rib-to-hole position s/D = 10.5

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Fig. 15

Streamwise and transverse velocity component at constant wall-normal distance zc/D = 0.80 for two different cooling Reynolds numbers with variation of the blowing rate, center rib-to-hole position s/D = 7.5 (obtained by PIV); (a) Rec,Dh = 10,000 and (b) Rec,Dh = 60,000

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Fig. 16

Hole mass fraction ratio and suction ratio as function of the coolant Reynolds number Rec,Dh

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Fig. 17

Streamwise and transverse velocity component at constant wall-normal distance zc/D = 0.80 at Rec,Dh = 10,000 and M = 1.00 with variation of the rib-to-hole position s/D (obtained by PIV)




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