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Research Papers

Numerical Investigation of a Film-Cooling Flow Structure: Effect of Crossflow Turbulence

[+] Author and Article Information
Jörg Ziefle

e-mail: joerg.ziefle@gmail.com

Leonhard Kleiser

e-mail: kleiser@ifd.mavt.ethz.ch
Institute of Fluid Dynamics,
ETH Zurich,
8092 Zurich, Switzerland

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received June 24, 2008; final manuscript received April 22, 2009; published online June 3, 2013. Assoc. Editor: Je-Chin Han.

J. Turbomach 135(4), 041001 (Jun 03, 2013) (12 pages) Paper No: TURBO-08-1056; doi: 10.1115/1.4023361 History: Received June 24, 2008; Revised April 22, 2009; Accepted October 18, 2012

Numerical simulation results using large-eddy simulation of a flow configuration relevant to the film cooling of turbine blades are presented. The flow configuration and the simulation parameters are chosen according to an experiment from literature, in which a hot turbulent crossflow over a flat plate is cooled by fluid issuing from a large isobaric plenum through a short inclined circular nozzle. Special attention is paid to the flow structure within the jet nozzle and the mixing region, as well as to the effect of the crossflow fluctuations thereon. To this end, the numerical results with the turbulent crossflow are compared to our previous data obtained with a steady mean-turbulent inflow profile. While the flow inside the nozzle is very similar for the two cases, large differences occur in the mixing region, where a much enhanced spreading of the coolant is observed with the turbulent crossflow. Consequently, the good agreement of the film-cooling efficiencies with the experimental data for the turbulent-crossflow case is contrasted by large deviations with the stationary inflow due to the lack of crossflow fluctuations.

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Figures

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Fig. 1

Schematic of the jet-in-crossflow configuration. (a) Lateral view and (b) top view. The gray areas symbolize the jet fluid. The dashed line in (a) marks the end of the sponge region, which is indicated by the shading transition from black to gray below it.

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Fig. 2

Reynolds stresses 〈u'iu'j〉/uτ (normalized with the friction velocity uτ) at the boundary-layer inlet. Lines: present inflow data generated with SEM [62,63] and symbols: reference data from [73]. ----/• Streamwise stresses 〈u'u'〉/uτ, ----/°spanwise stresses 〈v'v'〉/uτ, ---·---/× normal stresses 〈w'w'〉/uτ, ········/+ shear stresses 〈u'w'〉/uτ.

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Fig. 3

Isocontours of the vortex-identification measure [1] λ2 = −0.2 (except otherwise noted) of the instantaneous flow field. (a) Top view (steady-crossflow case), (b) top view (turbulent-crossflow case), (c) top view with λ2 = −0.01 (turbulent-crossflow case), (d) lateral closeup of nozzle region (steady-crossflow case), and (e) lateral closeup of nozzle region (turbulent-crossflow case). (a) and (d) and (b), (c), and (e) refer to the same instant of time, respectively. ① Turbulent streaks in crossflow (turbulent-crossflow case), ② outermost legs of horseshoe vortex, and ③ hairpin vortices. Solid walls appear as transparent gray surfaces.

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Fig. 4

Energy-density spectrum Epp of an instantaneous pressure signal at x = [x,y,z]T≈[3,0,0.25]T. (a) Steady inflow and (b) turbulent inflow. The time series were treated with a Hann window and the frequency f is expressed in terms of the Strouhal number St=fD/u∞.

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Fig. 5

Contour visualization of mean film-cooling efficiency 〈η〉 at the wall (z = 0). (a) Steady crossflow and (b) turbulent crossflow. The orifice is shown as a black ellipse. The contour lines mark ten equidistant intervals ranging from the minimum to the maximum of the value range indicated in the colorbar.

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Fig. 6

Positions of the cutting planes (a)–(f) within the nozzle in Fig. 7. The normal of cutting planes is parallel to the nozzle axis (vector n := [cos 35 deg, 0, sin 35 deg]T) and intersecting it in points −s n with s ∈ R. (a) s ≈ 1.743, (b) s ≈ 1.386, (c) s ≈ 1.029, (d) s ≈ 0.714, (e) s ≈ 0.357, and (f) s = 0.

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Fig. 7

Line-integral convolution (LIC) [75] visualization of the mean velocity field 〈[v,u⊥]T〉 in the film-cooling hole (with u⊥:=u·t and t:=[-sin 35 deg,0,cos 35 deg]T, for the stationary crossflow (top row) and the turbulent crossflow (bottom row). Details about the locations of the cutting planes (a)–(f) are given in Fig. 6 and are associated with the panels as indicated above them.

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Fig. 8

Line-integral convolution (LIC) [75] visualization of the mean velocity field 〈u〉 for the steady crossflow (upper row) and the turbulent crossflow (bottom row). (a)/(c) symmetry plane (y = 0) and (b)/(d) wall plane (z = 0).

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Fig. 9

Contour visualization of the mean flow field in the center plane y = 0. (a) and (b): Velocity magnitude 〈|u|〉 for the (a) stationary and (b) turbulent crossflows. (c) and (d): Film-cooling efficiency 〈η〉 for the (c) stationary and (d) turbulent crossflows. The vertical lines denote the locations of the cross sections in Figs. 10 and 11. Same contour legend as in Fig. 5.

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Fig. 10

Contour visualization of the mean velocity magnitude 〈|u|〉 in spanwise planes x = const. (marked in Fig. 8) for different streamwise positions x. Upper row: steady crossflow and lower row: turbulent crossflow. (a)/(e) x = 0, (b)/(f) x ≈ 0.872, (c)/(g) x = 4, and (d)/(h) x = 15. Same contour legend as in Fig. 5.

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Fig. 11

Contour visualization of the mean film-cooling efficiency 〈η〉 in spanwise planes x = const. (marked in Fig. 8) for different streamwise positions x. Upper row: steady crossflow, lower row: turbulent crossflow. Streamwise positions as in Fig. 10. Same contour legend as in Fig. 5.

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Fig. 12

Mean film-cooling efficiency 〈η〉. Left column: steady crossflow, right column: turbulent crossflow. ——— Present LES, –––– Sinha etal. [25] (a)/(b) Centerline effectiveness 〈η〉(x,y=0), (c)/(d) laterally averaged effectiveness 〈〈η〉〉y(x), and (e)/(f) local lateral effectiveness 〈η〉(x=const.,y) at three different streamwise locations. Lines: present LES, symbols: Sinha et al. [25] ——/× x=1-Δx, ––––/• x = 10 − Δx, —·—/° x=15-Δx, where Δx=1/(2 sin 35 deg)≈0.87 accounts for our different choice of coordinate origin compared to Sinha et al. [25].

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