Research Papers

Simulations of Slot Film-Cooling With Freestream Acceleration and Turbulence

[+] Author and Article Information
Yousef Kanani

Illinois Institute of Technology,
Mechanical, Materials and Aerospace
Engineering Department,
Chicago, IL 60616
e-mail: ykanani@hawk.iit.edu

Sumanta Acharya

Illinois Institute of Technology,
Mechanical, Materials and Aerospace
Engineering Department,
Chicago, IL 60616
e-mail: sacharya1@iit.edu

Forrest Ames

Mechanical Engineering Department,
University of North Dakota,
Grand Forks, ND 58202
e-mail: forrest.ames@engr.und.edu

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 11, 2017; final manuscript received December 4, 2017; published online January 30, 2018. Editor: Kenneth C. Hall.

J. Turbomach 140(4), 041005 (Jan 30, 2018) (11 pages) Paper No: TURBO-17-1156; doi: 10.1115/1.4038877 History: Received September 11, 2017; Revised December 04, 2017

Slot film cooling in an accelerating boundary layer with high freestream turbulence is studied numerically using large eddy simulations (LES). Calculations are done for a symmetrical leading edge geometry with the slot fed by a plenum populated with pin fins. The synthetic eddy method is used to generate different levels of turbulence and length scales at the inflow cross-plane. Calculations are done for a Reynolds number of 250,000 and freestream turbulence levels of 0.7%, 3.5%, 7.8%, and 13.7% to predict both film cooling effectiveness and heat transfer coefficient over the test surface. These conditions correspond to the experimental measurements of (Busche, M. L., Kingery, J. E., and Ames, F. E., 2014, “Slot Film Cooling in an Accelerating Boundary Layer With High Free-Stream Turbulence,” ASME Paper No. GT2014-25360.) Numerical results show good agreement with measurements and show the observed decay of thermal effectiveness and increase of Stanton number with turbulence intensity. Velocity and turbulence exiting the slot are nonuniform laterally due to the presence of pin fins in the plenum feeding the slot which creates a nonuniform surface temperature distribution. No transition to fully turbulent boundary layer is observed throughout the numerical domain. However, freestream turbulence increases wall shear stress downstream driving the velocity profiles toward the turbulent profile and counteracts the laminarizing effects of the favorable pressure gradient. The effective Prandtl number decreases with freestream turbulence. The temperature profiles deviate from the self-similar profile measured under low freestream turbulence condition, reflecting the role of the increased diffusivity in the boundary layer at higher freestream turbulence.

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Fig. 1

(a) Leading edge and test surface profile. The gray area shows the numerical domain. (b) The periodic module of the pin-finned plenum delivering coolant to the slot. The figure on the right shows the side view of the finned plenum and the slot-delivery channel; pin fins are indicated by the darkened regions. The a priori simulation data at plane section A-A are used as inflow conditions for the main simulations.

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Fig. 2

Acceleration parameter distribution with surface distance reported by Busche et al. [2]

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Fig. 3

Grid independence showing time- and laterally-averaged slot film cooling effectiveness

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Fig. 4

Numerical predictions of the time- and laterally-averaged adiabatic film cooling effectiveness at four turbulence levels

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Fig. 5

Comparison of slot film cooling effectiveness measurements and predictions with Hartnett's and Simon's correlations [4,16]: (a) Tu = 0.7%, (b) Tu = 3.5%, (c) Tu = 7.8%, and (d) Tu = 13.7%

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Fig. 6

Comparison of the predicted Stanton number distribution with measurements [2] over the surface

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Fig. 7

Contours of the time-averaged temperature field (or effectiveness) over the test surface for four freestream turbulence conditions

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Fig. 8

Contours of (a) the turbulence kinetic energy and (b) the blowing ratio at the slot exit (section B-B in Fig. 1)

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Fig. 9

Time-averaged velocity contour along a streamwise plane at a spanwise location of z/s = 3.75

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Fig. 10

Cooling effectiveness and blowing ratio. Main flow direction is from bottom to top. Bottom section shows blowing ratio distribution at the slot exit.

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Fig. 11

Iso-surfaces of the Q at the intermediate value colored by instantaneous velocity

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Fig. 12

Iso-surfaces of the Q at the high value colored by instantaneous velocity—Pin fins shown in this plot are not part of the main numerical simulation domain but accounted for in a priory simulation to specify slot inflow conditions

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Fig. 13

The time- and laterally-averaged streamwise velocity profiles scaled with the edge velocity Ue at various locations as a function of wall-normal coordinate scaled by the slot height y/s. See Fig. 16 for legend.

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Fig. 14

Velocity profiles in inner wall coordinates compared with viscous sublayer profile and universal log-law (gray dashed lines). See Fig. 16 for legend.

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Fig. 15

Distribution of integral quantities of the time- and laterally-averaged boundary layer: displacement thickness δ*, Shape factor H and Clauser parameter G. See Fig. 16 for legend.

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Fig. 16

Time- and laterally-averaged skin friction distribution over the test surface. Ludwieg and Tillmann correlation [32] (gray lines)—line types correspond to different turbulence levels.

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Fig. 23

Thermal boundary layer growth at different turbulence levels

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Fig. 22

Fully developed nondimensional temperature profiles for various turbulence levels

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Fig. 21

Turbulence intensity profiles at X/s = −5 (upstream of the slot) for Tu = 7.8%

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Fig. 20

Laterally averaged (a) streamwise and (b) wall normal turbulence intensity profiles

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Fig. 19

Laterally averaged shear stress profile as a function of y+ and y/s at various X/s (Tu = 7.8%)

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Fig. 18

Evolution of the peak of the laterally averaged streamwise turbulence intensity over the surface

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Fig. 17

Time- and laterally-averaged wall shear stress scaled with inlet velocity and Reynolds number




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