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Research Papers

Influence of Flow Structure on Compound Angled Film Cooling Effectiveness and Heat Transfer

[+] Author and Article Information
Vipluv Aga

Institute for Energy Technologies, Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerlandvipluv.aga@power.alstom.com

Reza S. Abhari

Institute for Energy Technologies, Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerland

J. Turbomach 133(3), 031029 (Feb 28, 2011) (12 pages) doi:10.1115/1.4002420 History: Received December 07, 2009; Revised May 31, 2010; Published February 28, 2011; Online February 28, 2011

Film cooling in turbine blades involves injecting cold air through small holes over the surface of the blade to thermally protect it against the incoming hot freestream. Compound angled film cooling, in which the injected jet is angled laterally with respect to the streamwise flow direction, is used in industrial designs owing to their lower cost of manufacture compared with shaped geometries but a high coolant spread. The current study incorporates flow structure measurements of film cooling injection flows inclined at 30 deg to a flat surface with lateral angles of 15 deg, 60 deg, and 90 deg to the freestream. Blowing ratios of 1–2 and density ratios of 1–1.5 are studied. Three dimensional velocity measurements are carried out through high resolution stereoscopic particle image velocimetry. It is observed that the typical counter-rotating vortex pair structure associated with streamwise coolant injection is replaced with a single large vortex, which causes a more lateral spread of the coolant. Infrared thermography measurements are made for the same operating points using the super position principle, which allows calculation of adiabatic effectiveness and heat transfer coefficient. The adiabatic effectiveness is high at low blowing ratios for compound angled injection due to greater proximity of the coolant jet to the wall. At higher blowing ratios, the detrimental effects on effectiveness due to jet lift-off are counteracted by the greater coolant spread due to asymmetric primary vorticity. The heat transfer coefficient is also enhanced especially in the downstream region for high compound angles. The average heat transfer coefficient due to very large compound angles is not very sensitive to changing momentum flux ratios.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Definition of the coordinate system and geometrical parameters

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Figure 2

Schematic and diagram of the 3D stereoscopic PIV setup

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Figure 3

Schematic of the infrared thermography measurement setup

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Figure 4

Contours of normalized axial velocity and plane tangential flow vectors at X=4 for β=15 deg, 60 deg, 90 deg for blowing ratio of 2 and density ratios of 1 and 1.5

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Figure 5

Normalized streamwise vorticity isosurfaces for β=15 deg, BR=2, DR=1, and IR=4

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Figure 6

Normalized streamwise vorticity isosurfaces for β=60 deg, BR=2, DR=1.5, and IR=2.67

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Figure 7

Normalized streamwise vorticity isosurfaces for β=60 deg, BR=1, DR=1, and IR=1

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Figure 8

Normalized streamwise vorticity isosurfaces for β=90 deg, BR=2, DR=1.5, and IR=2.67

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Figure 9

Streamwise circulation Γ=∮AVx,ndA evolution with IR-scaled nondimensionalized downstream distance ξ on a semilog scale for all compound angled geometries at DR=1.5

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Figure 10

Data fits on a semilog plot for the streamwise circulation evolution for β=15 deg, 60 deg, and 90 deg at DR=1.5 of the form Γx,n=A ln(ξ)+B, or if y-axis is made positive by taking the absolute value of circulation, the same fit can be formulated as a power law of the form Γx,n=A(ξ)−1/B, B>1

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Figure 11

Normalized streamwise vorticity isocontours at Z=0.5 above the wall for BR=1, DR=1.5, and IR=2.67

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Figure 12

Contours of adiabatic effectiveness η=(Th−Taw)/(Th−Tc) for BR=1, DR=1.5, and IR=0.67 for three compound angled injection cases

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Figure 13

Normalized streamwise vorticity isocontours at Z=0.5 above the wall for BR=2, DR=1.5, and IR=2.67

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Figure 14

Contours of adiabatic effectiveness η=(Th−Taw)/(Th−Tc) for BR=2, DR=1.5, and IR=2.67 for three compound angled injection cases

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Figure 15

Laterally averaged adiabatic effectiveness with downstream distance X compared with published correlation of Ref. 18 for streamwise oriented jets

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Figure 16

Laterally averaged adiabatic effectiveness with downstream distance X for β=60 deg and 90 deg at DR=1.5

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Figure 17

Contours of normalized heat transfer coefficient hf/h0 for BR=1, DR=1.5, and IR=0.67 for three compound angled injection cases

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Figure 18

Normalized wall-normal vorticity isocontours at Z=0.5 above the wall for BR=1, DR=1.5, and IR=0.67

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Figure 19

Contours of normalized heat transfer coefficient hf/h0 for BR=2, DR=1.5, and IR=2.67 for three compound angled injection cases

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Figure 20

Normalized wall-normal vorticity isocontours at Z=0.5 above the wall for BR=2, DR=1.5, and IR=2.67

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Figure 21

Laterally averaged heat transfer coefficient augmentation hf/h0 compared with published results from Refs. 33-34,20

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Figure 22

Laterally averaged heat transfer augmentation hf/h0 at DR=1.5

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Figure 23

Spatially averaged NHFR with respect to IR for S/D=4

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